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283 Cards in this Set
- Front
- Back
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What is the brain primarily composed of?
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Neuroepithelial cells
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Which gyrus is displaced in subfalcine herniation?
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The cingulate gyrus
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What does uncal herniation look like?
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Effacement of the ambient (suprasellar) cistern and contralateral hydrocephalus.
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How do you distinguish a small neoplasm from a small infarct?
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-DWI, perfusion imaging, MR spectroscopy
-If these aren’t available, followup imaging in 3 weeks may help -All infarcts should be smaller by then |
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What are some signs that a tumor is extra-axial?
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-White matter buckling—inward compression of the white matter
-Thinning of the fronds of white matter -Maintenance of the gray-white interface |
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What are some signs that a tumor is intra-axial?
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-White matter fronds are thickened
-Gray-white differentiation is blurred |
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How do you define the tumor margin?
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-It can be hard
-It is typically beyond the enhancing area -Spectroscopy is helpful |
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What is the FLAIR sequence useful for?
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Improved visualization of abnormal signal involving the periventricular and peripheral areas
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What is the unenhanced T1 useful for?
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Distinguishing inherent T1 shortening (from things like hemorrhage) from contrast enhancement
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What do intra-axial tumors look like on CT?
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-Hypodense
-Variable surrounding white matter edema |
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What do intra-axial tumors tend to look like on MR?
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-T2 bright, T1 dark
-Variable surrounding vasogenic edema |
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What does calcification within the tumor look like on MR?
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-Usually it causes marked hypointensity on T1 and T2
-Occassionally, because of the surface area of the crystals producing T1 shortening, calcification may appear bright on T1 |
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What does hyperacute (less than 6 hours) hemorrhage look like on MR?
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-T1 and T2 prolongation
-Dark on T1, bright on T2 |
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What is the primary blood product in hyperacute hemorrhage?
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Oxyhemoglobin
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What does acute hemorrhage (6-24 hours) look like on MR?
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-Mild T1 prolongation (dark on T1)
-Moderate T2 shortening (darker on T2) |
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What is the primary blood product in acute hemorrhage?
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Deoxyhemoglobin
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What does hemorrhage look like after 3-4 days?
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-Intracellular methemoglobin causes T1 and T2 shortening
-Bright on T1, dark on T2 -Extracellular methemoglobin (when RBC’s lyse) causes T1 shortening and T2 prolongation -Bright on T1 and bright on T2 |
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What is the primary blood product in chronic hemorrhage (older than 10-14 days)?
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Hemosiderin appears as a rim
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What does hemosiderin look like?
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-Extreme T2 shortening
-Peripheral markedly hypointense rim |
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Why is hemosiderin found in the periphery of hemorrhages?
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Because macrophages come in and carry the hemosiderin to the periphery
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What does acute hemorrhage look like on CT?
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Hyperdense
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What does hemorrhage look like after 1-3 weeks on CT?
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Isodense to normal brain tissue
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What does hemorrhage look like after 3 weeks on CT?
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Hypodense to parenchyma, simulating the attenuation of CSF
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What does intratumoral hemorrhage look like?
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-It’s heterogeneous
-The hemorrhage is often intermittent, producing a mixture of the blood breakdown products -Hemorrhage can occur in cystic or necrotic portions of the tumor producing blood-blood or fluid-blood levels -Normal deoxyhemoglobin evolution is delayed -There is no peripheral hemosiderin ring because the macrophages can’t penetrate the tumor |
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How can you tell tumor hemorrhage from simple parenchymal hemorrhage?
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Look for:
-Nonhemorrhagic mass adjacent to the hemorrhage -Persistence of T2 prolongation (=edema or the tumor itself) -Mass effect |
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Which tumors are known for their propensity to hemorrhage?
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-Choriocarcinoma
-Mets from melanoma, thyroid, and renal cell carcinoma -Oligodendroglioma These will have multiple hemorrhagic lesions within the brain -Multiple AVMs, occurring either de novo or from radiation therapy can have a similar appearance BUT they won’t have surrounding edema |
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What things produce focal T1 shortening (bright on T1)?
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-Hemorrhage
-Melanin within a melanoma -Fat within lipomas or dermoids |
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What does fat look like on T2?
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-Intermediate signal, follows the signal of subcutaneous fat
-Chemical shift artifact on T2 confirms the presence of fat |
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Which tumors tend to have high cellular density?
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-Lymphoma
-Pineoblastoma -Neuroblastoma -Medulloblastoma -Mets from melanoma, lung, colon, and breast ca. |
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What do dense tumors look like on MR?
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Hypointense on T2, reflecting high nucleus:cytoplasm ratio
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Enhancement occurs because of one principle:
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-The breakdown of the blood-brain barrier
-The endothelium of the cerebral arteries allows passage of only small molecules through their tight jnctions and narrow intercellular gaps |
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What conditions cause breakdown of the BBB?
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-Intra-axial tumors
-Inflammatory diseases -Subacute infarcts -Post-op gliosis -Radiation necrosis |
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Why don’t some tumors enhance?
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-Low-grade tumors might not
-They presumably form new capillaries that are quite similar to the native cerebral capillaries with their own BBB -More aggressive, high-grade neoplasms tend to form fenestrated capillaries |
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Which areas of the brain enhance normally?
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-Choroid plexus
-Pituitary and pineal glands -Tuber cinereum -Area postrema These areas have no BBB |
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When should a pts first scan after brain surgery occur? Why?
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-Within 72 hours after surgery
-To serve as a baseline scan for future follow-up -Granulation tissue occurs in all post-op neurosurgery patients -Once formed, it may persist in the post-op site and within the dura for weeks to months, and it enhances with contrast, making it impossible to distinguish from residual tumor -If there is enhancement on the immediate post-op scan, then it’s residual tumor. |
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What does diffuse white matter injury from radiation therapy look like?
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-Geographic white matter hyperintensity on T2 conforming to the selected radiation port
-Affected areas do not enhance |
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What does radiation necrosis look like?
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-It is virtually indistinguishable from recurrent tumor
-Both have mass effect and enhancement -MRS, DWI, perfusion and PET are helpful |
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Does radiation necrosis restrict diffusion?
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-Yes, the area is composed of heavily necrotic tissue
-The overwhleming majority of brain tumors do not cause restricted diffusion |
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How does perfusion help in evaluating radiation necrosis?
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-Radiation necrosis should not have increased perfusion
-Many tumors will have increased perfusion |
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How does PET help in evaluating radiation necrosis vs. residual tumor?
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-Radiation necrosis should show normal to decreased metabolism
-Recurrent tumor is usually increased, especially if the original tumor was high-grade |
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Which brain tumors tend to occur in women?
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"Men Naturally Prefer Pretty women"
-Meningioma -Neurofibroma -Pineocytoma -Pituitary tumor |
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Which brain tumors tend to occur in men?
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"Girls Have Pretty Parts Men Can’t Cuddle"
-Glioblastoma multiforme -Hamartoma of the tuber cinereum -Pineal germinoma (10:1) -Pineal parenchymal tumor -Medulloblastoma -Choroid plexus papilloma -CNS lymphoma |
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What percent of CNS tumors are gliomas?
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40-50%
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What percent of gliomas are astrocytomas?
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70%
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What is the most common type of astrocytoma?
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Glioblastoma multiforme
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How many histologic grades of astrocytomas are there?
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Four
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Examples of grade I astrocytomas:
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-Pilocytic astrocytoma
-Subependymal giant cell astrocytoma |
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Why can low grade tumors look diffuse?
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Because they don’t have a capsule
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What are grade III astrocytomas called?
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Anaplastic astrocytomas
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What is the most malignant form of astrocytoma called?
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Glioblastoma multiforme
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What do low grade astrocytomas tend to look like?
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-Slow-growing
-Usually well-demarcated but can appear diffuse (remember that they don’t have a capsule) -No necrosis -Hemorrhage is rare -Surrounding edema is rare -20% calcified -Enhancement ranges from none to minimal |
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Can low grade astrocytomas degenerate into more aggressive tumors?
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Yes
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Four avenues of brain tumor spread:
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-White matter tracts
-Natural passages (e.g., Virchow-Robin spaces) -Along subpial or subependymal surfaces -Across the meninges (rarely) |
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What do anaplastic astrocytomas tend to look like?
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-Heterogenous mass with necrosis and hemorrhage common
-Edema is common -May have focal or patchy enhancement (more avid enhancement suggests GBM) -Neovascularity, but prominent flow voids are suggestive of degeneration into GBM |
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What is paradoxical about astrocytoma’s gross appearance?
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-The low grade astrocytomas are frequently ill-defined as they insinuate themselves thorugh the neurons and other supporting cells that make up the scaffold of the brain
-Highly malignnat GBM may be more macroscopically well-defined. |
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Where is the most common location for a GBM?
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-Deep white matter of the frontal lobe
-This is the largest lobe of the brain (I didn’t know that!) -This is followed by the temporal lobe and the basal ganglia |
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Describe the classic appearance of a GBM:
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-Expansile mass with central necrosis, ring enhancement, and a large surrounding region of vasogenic edema
-Heterogeneous and lobulated -Occasional calcifications -Necrosis and hemorrhage are common -Highly vascular, with multiple flow voids -More than 90% of all GBMs show irregular, ringlike enhancement |
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What does the tumor nidus of a GBM look like on MR?
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-T1 and T2 prolongation (dark on T1, bright on T2) compared to gray matter
-Because of the cellular material, these cystlike areas look slightly different from CSF |
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How does ring enhancement of a tumor look different from ring enhancement of an abscess?
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-Irregular ring enhancement=tumor
-Smooth ring enhancement=abscess Also, an abscess rim typically is hyperintense on T1 and hypointense on T2; this is not seen in tumors |
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What entities can have a butterfly appearance?
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-Glioblastoma multiforme
-CNS lymphoma -Infections and demyelinating processes can involve the corpus and have a butterfly appearance |
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What causes the butterfly appearance of a GBM?
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Bihemispheric spread through the corpus callosum
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*Abnormal signal in the corpus callosum in these lesions is secondary to the disease process itself and does not simply represent vasogenic edema*—Why?
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-Because the callosal fibers and projection fibers of the itnernal capsule are packed so tightly together that edema fluid cannot be conducted through them
-Therefore, if a neoplasm is suspected, any T2 hyperintensity seen in the corpus callosum or internal capsule must be considered secondary to neoplastic spread and not a consequence of vasogenic edema. |
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How are GBMs treated typically?
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Surgical resection, chemotherapy, and radiation therapy
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After treatment, how do GBMs typically respond?
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-They will usually shrink and symptoms will improve
-Usually within 1 year after surgery, the tumor frequently recurs |
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What do treated brain tumors look like?
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Necrotic and calcified
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Where do astrocytomas tend to occur in children?
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-Along the optic pathways
-Hypothalamus -Near/in the third ventricle |
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Name the grade I astrocytomas:
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-Pilocytic astrocytoma
-Subependymal giant cell astrocytoma |
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Name the grade II astrocytomas:
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-Fibrillary astrocytoma
-Gemistocytic astrocytoma -Protoplasmic astrocytoma -Pleomorphic xathoastrocytoma (PXA) |
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Describe a PXA:
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-Distinct entity seen in adolescents and young adults
-Heterogeneous mass with a soft tissue component located peripherally along the meningocerebral interface |
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What percent of low grade astrocytomas degenerate into higher grade lesions?
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10%
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List the typical ring-enhancing lesions:
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"MAGIC DR"
-Metastasis -Abscess -Glioblastoma multiforme -Infarct (subacute) -Contusion -Demyelinating disease -Resolving hematoma, radiation necrosis |
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What is gliomatosis cerebri?
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-Rare neuroepithelial neoplasm
-Widespread infiltration of neoplastic cells (probably astrocytes) -By definition, at least three lobes are involved -Despite diffuse involvement, symptoms are often mild -Frequently lesions smolder for week-years until erupting into full blown GBM -Poor prognosis |
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What does gliomatosis cerebri look like?
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Two imaging appearances:
#1: Diffuse involvement of the cerebral white matter without mass -CT looks normal -MR shows diffuse T1 and T2 prolongation, particularly in the centrum semiovale, hypothalamus, basal ganglia, and thalamus -Relative lack of mass effect is striking -Gray-white distinction is lost -Enhancement is typically absent. #2: Above feature with an additional discrete mass |
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What entity does gliomatosis cerebri look like?
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PML
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Why is MRS helpful in evaluating gliomatosis cerebri?
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It helps identify the more biologically aggressive regions to direct potential sites for biopsy
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Where are oligodendrogliomas usually located?
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Frontal lobe
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What do oligodendrogliomas look like?
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-Calcifications
-Hemorrhage and cysts occur in 20% -Extends to cortex, where it may erode the calvarium -Hypointesnse on T1, hyperintense on T2 -1/3 with vasogenic edema -2/3 enhance, variable degrees of enhancement |
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What is an oligoastrocytoma?
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Oligodendrogliomas are frequently combined with elements of astrocytes and labelled as a mixed glioma (e.g., oligoastrocytoma)
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What percent of oligodendrogliomas calcify?
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70%
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What percent of astrocytomas calcify?
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25%
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Is a calcified lesion more likely to be an oligodendroglioma or an astrocytoma?
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Astrocytoma—because they’re so much more common
(even though they are not as commonly calcified as oligodendrogliomas) |
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Differential for calcified glial brain tumors:
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“Old Elephants Age Gracefully”
-Oligodendroglioma -Ependymoma -Astrocytoma -Glioblastoma multiforme |
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What are the variant forms of oligodendroglioma?
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Oligoastrocytoma
-Looks just like an oligodendroglioma on imaging Anaplastic oligodendroglioma -Can mimic GBM |
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What type of lymphoma typically is seen in primary CNS lymphoma?
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B cell non-Hodgkin
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What are the four most common primary brain neoplasms?
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-GBM
-Meningioma -Low-grade astrocytoma -Primary CNS lymphoma |
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What does CNS lymphoma look like on path?
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Small blue cells with high nucleus-to-cytoplasm ratio packed tightly together in the perivascular space (Virchow-Robin)
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Where does CNS lymphoma tend to be located?
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-Adjacent to the ventricular system or along the leptomeninges
-85% are supratentorial; 10% occur in the cerebellum |
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What does CNS lymphoma look like?
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-Hyperdense mass on CT
-Hypointensity on T1 contrasts with surrounding edema on MR -At least some enhancement in virtually all lesions -Calcification and hemorrhage are rare |
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How does the appearance of CNS lymphoma change in immunocompromised pts?
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Increased predilection for necrosis and multifocality
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How do CNS lymphomas tend to spread?
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-Subependymally
-Bihemispheric involvmenet via the corpus callosum (butterfly glioma pattern) may be seen |
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How can you tell toxoplasmosis apart from lymphoma?
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-Toxo is not associated with subependymal spread because it is an abscess
-Toxo is more likely to be located at the gray-white interface or in the basal ganglia -Toxo has ring-like enhancement often with a highly characteristic enhancing mural nodule -DWI, PET, thallium, MRS can differentiate the two |
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What can you do if DWI, MRS, thallium, or perfusion aren't available to help you distinguish toxo from lymphoma?
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Reimaging after 3 weeks of toxo therapy may help—toxo lesions should decrease in size
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Other entities in the differential for toxo/CNS lymphoma-like lesions?
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-Mets
-Focal cerebritis |
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What are gangliogliomas composed of?
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-Glial cells and differentiated neurons (ganglion cells)
-In contrast, gangliocytoma and ganglioneuromas are neuronal tumors without a glial component |
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What is the most common tumor seen in patients with chronic temporal lobe epilepsy?
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Gangliogliomas
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Where are gangliogliomas most commonly found?
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-Temporal lobe, floor of the third ventricle
-But they can occur anywhere, even in the spinal cord |
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Prognosis with gangliogliomas/gangliomas?
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Good; they’re relatively low grade
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What age group gets gangliogliomas/gangliomas?
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-80% in patients younger than 30 years
-Males are slightly more affected |
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What do gangliogliomas/gangliomas look like?
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-Hypodense or isodense on CT
-Well-circumscribed -Little mass effect or surrounding edema -Peripheral location and calcification are frequent features -On MR, hypointense-isotense to gray matter on T1, hyperintense on T2 |
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What is a desmoplastic infantile ganglioglioma? Who gets them? How do they present? Prognosis?
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-Rare variant of ganglioglioma
-Almost always seen in the first year of life -Boys are affected twice as often as girls -Rapidly expanding head circumference is the most common clinical finding -Surgical resection is difficult because of adherence of the desmoplastic tissue to the dura |
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What does a desmoplastic infantile ganglioglioma look like?
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-Very large heterogenous mass with both cyst-like and solid components
-Solid soft tissue region is almost always located along the meningocerebral interface, similar to PXA (pleomorphic xanthoastrocytoma) -Intense enhancement of the soft tissue component |
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What tumor is most commonly associated with refractory partial complex seizures?
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Dysembryoplastic neuroepithelial tumor (DNET)
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Who gets DNETs?
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Patients are young 10-30 years
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What do DNETs look like?
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-Peripheral in location
-Almost always involves the cortical gray matter -Some lesions produce a “soap bubble” appearance with exophytic extension beyond the normal cortical gray matter margin -Pressure erosion effect in the adjacent skull may be seen |
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Prognosis of DNETs?
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Prognosis is excellent, even if only partial resection is attained
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List congenital brain tumors in infants younger than 2 mos:
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-Teratoma (most common)
-Primitive neuroectodermal tumors (PNET) -Astrocytoma -Choroid plexus papilloma -Ependymoma -Medulloepithelioma -Germinoma -Angioblastic meningioma -Ganglioglioma |
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What age group gets SPNETs?
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Early childhood (mean age is 5)
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What cells do SPNETs arise from?
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Bipotential precursor cells of the germinal matrix with the ability to differentiate along either glial or neuronal cell lines
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What tumors are similar to SPNETs on histo?
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-Medulloblastoma
-Ependmoblastoma -Pineoblastoma -Retinoblastoma |
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What do SPNETs look like?
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-Large well-demarcated heterogeneous mass with both solid and cystlike areas
-Within the deep cerebral white matter -Periventricular or intraventricular location with hydrocephalus is common. -Calcification is very common -Necrosis and hemorrhage is common -Vasogenic edema is variable -Hypointense on T1 and isointense-hypointense on T2 compared to gray matter |
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What fraction of all brain tumors are mets?
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About 1/3
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Most common primary with mets to the extra-axial spaces?
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-Breast
-Prostate -Lung -Neuroblastoma |
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Most common primary with mets to the intra-axial areas?
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-Lung
-Breast -Melanoma -Colon |
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Most mets are supratentorial. Which primary tends to have mets in the posterior fossa?
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Renal cell (makes sense since kidneys are posterior)
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Which mets tend to be hemorrhagic?
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-Melanoma
-Renal cell -Thyroid -Choriocarcinoma |
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What do mets look like?
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-Multiple foci located at the gray-white junction
-Hypodense on CT -Hypointense on T1, variable on T2 -Marked vasogenic edema -Intense enhancement (ring or nodular) |
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How can mets look different on single vs triple dose gadolinium studies?
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-Triple dose studies may reveal additional lesions when only a single lesion is present on single dose
-This is important since single lesions may be surgically resectable |
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How do pts with leptomeningeal spread of tumor present?
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Patients commonly present with cranial nerve palsies
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Which tumors tend to exhibit leptomeningeal spread?
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Primary CNS malignancies, extracranial adenocarcinoma (especially of lung or breast origin), leukemia, or lymphoma
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What does leptomeningeal spread of tumor look exactly like?
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Not surprisingly, its imaging appearance may exactly mimic that of meningitis.
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What does leptomeningeal spread of tumor look like?
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-Postcontrast MR is the imaging modality of choice and detection is enhanced using fat suppression, FLAIR, or magnetization transfer techniques.
-Diffuse or nodular enhancement of the leptomeninges -The presence of hydrocephalus in a patient with a known malignancy should raise the possibility of this diagnosis. |
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Which sequence might obscure bony mets?
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As with metastases to the spinal vertebral bodies, those that arise in the skull may be obscured if only contrast-enhanced T1WIs are reviewed.
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Where do most pediatric intracranial neoplasms occur?
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The posterior fossa is the most common site for intracranial neoplasms in the pediatric population.
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What are the most common primary pediatric intracranial neoplasms?
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Medulloblastoma and cerebellar astrocytoma account for about two
thirds of all posterior fossa neoplasms in children, with ependymoma and brainstem glioma composing the remaining third |
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Where in the posterior fossa do medulloblastomas tend to occur?
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-The cerebellar vermis (85%)
-Extension into the adjacent fourth ventricle and subsequent development of hydrocephalus is common. -Subarachnoid CSF spread is common (33%) at the time of diagnosis. -Cerebellopontine angle involvement is rare. |
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What does a medulloblastoma tend to look like on CT and MR?
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Hyperdense on CT
Hypointense on T1WIs Variable on T2WIs Hemorrhage is rare |
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Where in the posterior fossa do pilocytic astrocytomas tend to occur?
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Cerebellar vermis, hemisphere
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What do pilocytic astrocytomas look like?
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There are two imaging manifestations:
#1: Cystic, with enhancing solid mural nodule (66%). The cyst wall may or may not enhance. #2: Solid masses with or without a necrotic center, sometimes calcified. -Hemorrhage and vasogenic edema are rare. -On CT, they present as a well-demarcated vermian or hemispheric mass, with the solid portion being isodense or hypodense to brain tissue. -On MR, they are isointense to hypointense compared to gray matter on T1WIs and hyperintense compared to gray matter on T2WIs. -The cystic portion usually contains proteinaceous fluid and therefore does not exactly follow the signal intensity of CSF. |
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What do ependymomas look like?
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-Foraminal extension ("toothpaste" tumors)
-Heterogeneous on CT and MR -Intense but heterogeneous enhancement |
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Where in the posterior fossa do ependymomas tend to occur?
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Fourth ventricle
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What do brainstem gliomas look like?
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-Expansile brainstem
-Isodense to hypodense on CT -Hypointense on T1WIs -Hyperintense on T2WIs |
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What is the most common primary brain tumor in the posterior fossa of adults?
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The hemangioblastoma is the most common primary cerebellar neoplasm in the adult population.
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What is the single most common pediatric CNS malignancy?
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Pilocytic astrocytoma
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What age group gets medulloblastomas?
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Most cases manifest before 10 years of age, with peak incidence between 4 and 8 years. A smaller peak is also seen between 15 and 35 years of age, and the tumor may occasionally manifest well into the older adult ages.
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Which gender tends to get medulloblastomas?
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Males are more commonly affected (60%).
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What cells do medulloblastomas arise from? How does this affect its presentation?
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When the tumor arises in older children and adults, it tends to be located more laterally within the cerebellar hemisphere. Accordingly, the tumor is believed to arise from undifferentiated bipotential precursor cells, which are located in the cerebellar midline early in life and then migrate more laterally with advancing age.
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Do medulloblastomas tend to be more benign or more aggressive?
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Medulloblastoma is a highly malignant neoplasm (WHO grade IV) with rapid growth. Subarachnoid CSF spread is common (33%) at the time of diagnosis.
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How can you tell a medulloblastoma apart from a pilocytic astrocytoma?
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The single most reliable way to differentiate a medulloblastoma from an astrocytoma on cross-sectional imaging studies is to utilize a noncontrast CT scan; the astrocytoma will usually be hypodense and the medulloblastoma will almost never be hypodense.
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Why is it super-important to get scans of the entire spine before resection of a medulloblastoma?
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Postoperative granulation tissue and hemorrhagic debris interferes with the accurate detection of “drop” metastases during the first 6 to 8 weeks after surgery, thereby delaying appropriate therapy and potentially threatening survival.
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Aside from the posterior fossa, where do pilocytic astrocytomas tend to occur?
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Other common locations include the optic pathways and hypothalamus.
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What percent of NF-1 pts get pilocytic astrocytomas?
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It's present in 15% to 21% of all NF1 patients, usually in sites other than the cerebellum.
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How can you be sure something is a cyst on MR?
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Truly cystic lesions can only be confidently identified by the presence of fluid–fluid levels or wave pulsation phenomenon.
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The appearance of a cystic cerebellar mass with an enhancing mural nodule should suggest two possible diagnoses:
What's the best way to tell the difference? |
-Pilocytic astrocytoma
-Cerebellar hemangioblastoma The best discriminator between the two is the patient's age |
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What's the most common adult tumor of the cerebellum?
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Metastasis is the most common cerebellar adult neoplasm overall
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What cells do ependymomas arise from?
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The tumor arises from the ependymal cells that line the ventricular system and the central canal of the spinal cord.
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Where do ependymomas arise?
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-The tumor is most commonly seen as an intraventricular or spinal cord mass.
-In children, 60% to 70% occur within the posterior fossa, with 70% of those centered within the fourth ventricle. -Curiously, there is a predilection of the tumor to originate within the brain itself (i.e., intra-axial) instead of the ventricular system when it arises supratentorially. |
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Is an ependymoma a low or high grade tumor?
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It's considered to have fairly low biologic behavior and is considered WHO grade II
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Why are epndymomas called "toothpaste" tumors?
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When it arises in the fourth ventricle, this soft and pliable tumor frequently extends through the foramina of Luschka or Magendie into the cerebellopontine angle (it squeezes out like toothpaste)
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What should you think of if you see subarachnoid seeding with an ependymoma?
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Subarachnoid seeding is rare, and its presence should suggest the possibility of a malignant ependymoma.
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What location would you NOT want to have an ependymoma?
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When the tumor arises in the fourth ventricle, gross total resection is difficult to attain, leading to increased recurrence and decreased survival.
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What do ependymomas look like on CT and MR?
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-On CT, these tumors are isodense with a mixture of calcification, cystic change, and even hemorrhage, producing an overall heterogeneous appearance.
-This pattern is also seen on MR, where they are isointense compared to gray matter on T1WIs and hyperintense to gray matter on T2WIs. -Following contrast, there is heterogeneous enhancement of the solid component. -Extraventricular extension from the fourth ventricle through the adjacent foramina is highly characteristic |
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What type of tumors are pediatric brainstem gliomas usually? What grade are they?
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The overwhelming majority of such tumors are astrocytomas; they range the entire WHO classification but most often are WHO grade I or II lesions.
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What do brainstem gliomas look like?
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On CT, focal, hypodense to isodense expansion of the brainstem, with extremely variable enhancement that may change with time.
-On MR, typical prolongation of T1 and T2 is seen. T2WIs are best to assess the true extent of the tumor, because the signal hyperintensity of the tumor contrasts sharply with the relatively low signal of normal white matter. -Detection of a brainstem glioma may be difficult. Three key imaging features: #1: Exophytic growth into the adjacent cisternal spaces occurs in about 60% of cases. #2: If the ventral portion of the pons extends beyond the anterior margin of the basilar artery, then abnormal enlargement of the pons is present. #3: Alteration of the normal fourth ventricle contour provides a useful clue (flattening of the floor, the ventricle itself may be displaced posteriorly, and the ventricle may be rotated if there is involvement of the lateral recesses) |
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Prognosis for a brainstem glioma? Typical treatment?
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The prognosis for patients with a brainstem glioma is guarded (10% to 30% 5-year survival). Chemotherapy and radiation therapy, rather than surgery, are the main treatment options. The tumor is difficult to treat and nearly always recurs within 2 years after completion of therapy.
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Differential for an enlarged pons?
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-Brainstem glioma
-Encephalitis -Tuberculoma -Acute disseminated encephalomyelitis -Infarction -Resolving hematoma -Vascular malformation The presence of blood breakdown products on MR makes detection of one of the vascular causes fairly straightforward. However, encephalitis and tuberculoma cannot be distinguished from a brainstem glioma based on imaging characteristics alone. |
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Most common site for a brainstem glioma?
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Pons
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When a brainstem glioma extends through the foramen magnum, what can it be confused with? How can you tell the difference?
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When a brainstem glioma extends through the foramen magnum, it may resemble an ependymoma. However, ependymomas are separate from the brainstem and typically enhance more vigorously than brainstem gliomas.
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What are cerebellar hemangioblastomas? Who gets them?
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-Capillary hemangioblastomas are benign neoplasms of endothelial origin (although they are prone to recurrence)
-They are most common in young and middle-aged adults and are the most common primary cerebellar neoplasm in the adult population. -Approximately 4% to 20% occur as part of the von Hippel-Lindau syndrome, in which case they are often multiple. |
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Where are hemangioblastomas usually found?
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They occur most often in the cerebellar hemispheres; other sites of involvement include the spinal cord (especially the cervical portion), medulla, and even the cerebral hemispheres (very rare).
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What do hemangioblastomas look like?
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-The classic appearance is a well-defined cystic mass with an intensely enhancing mural nodule (60% of cases).
-Because the tumor nidus receives its blood supply from the pia mater, the nodule (which represents the tumor itself) is always superficial in location. -Because of the highly vascular nature of the nodule, intense enhancement is the rule -On MR, they manifest as cystlike masses with hypointensity on T1WIs and hyperintensity on T2WIs compared to gray matter. -Surrounding edema may be present. -Serpiginous flow voids within the nodule may be seen in some cases. -Up to 40% are entirely solid and have a nonspecific imaging appearance. -In the less common presentation of a solid mass, the margins are usually ill-defined, and occasionally hemorrhage is present. |
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What is a dysplastic cerebellar gangliocytoma?
What does it look like? |
-Hamartoma
-Half of all patients with the disease also have Cowden disease, an autosomal dominant phacomatosis associated with colonic polyps, cutaneous tumors, meningioma, and glioma, as well as thyroid and breast neoplasms. -The CT appearance is often normal. -The classic feature seen on MR imaging is a “striated” cerebellar mass on both T1WIs and T2WIs with minimal surrounding vasogenic edema and no enhancement on postcontrast studies. |
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What is a tumor that mimics the appearance of a medulloblastoma in the posterior fossa in kids? How can you tell them apart?
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-Atypical teratoid/rhabdoid tumor (ATRT)
-ATRT frequently extends into the adjacent cerebellopontine cistern, a feature rarely associated with a medulloblastoma. |
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What's the most common extra-axial tumor?
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Meningioma is by far the most common extra-axial neoplasm of adults and accounts for 15% of all intracranial neoplasms, second only to gliomas in overall prevalence.
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What tumor is associated with Cowden's disease?
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Dysplastic cerebellar gangliocytoma
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Are men or women more commonly affected by meningiomas?
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Women (2:1)
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How can pregnancy effect meningiomas?
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Because the tumor is hormonally sensitive, it may increase in size during pregnancy.
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What should multiple meningiomas (or meningiomas in children) make you think of?
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Multiple tumors (up to 9% of all cases) are associated with neurofibromatosis.
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Where is the most common site for meningiomas?
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They are most frequently found in parasagittal or convexity locations
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What percent of meningiomas are found in the spine?
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About 2% to 3% are intraspinal, with the thoracic spine the most common location.
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What cells do meningiomas arise from?
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-Meningioma arises from arachnoid cap, cells with some probable contribution from dural fibroblasts and pial cells.
-It is believed that intraventricular meningiomas arise from arachnoidal cap cell rests that are buried within the choroid plexus. |
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Two shapes of meningiomas:
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-Globular
-En plaque |
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Are meningiomas benign or malignant?
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-Malignant variants of meningiomas are rare, occurring in about 1% of cases.
-It is not possible to reliably distinguish malignant from nonmalignant meningiomas based on imaging characteristics alone. |
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Plain film findings of meningiomas?
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These tumors can be suspected by the findings of focal sclerosis, prominent dural grooves from enlarged middle meningeal arteries, and calcification.
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CT findings of meningiomas?
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-On CT, a well-defined hyperdense (85%) mass with variable surrounding edema and intense and homogeneous enhancement on postcontrast studies is highly characteristic.
-Hyperostosis of the adjacent inner table is noted about 40% of the time. -Calcification is seen in 10% to 20% of cases. |
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MR findings of meningiomas?
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-The tumor is typically isointense to hypointense to gray matter on T1WIs and isointense to hyperintense to gray matter on T2WIs.
-Hyperintensity on a T2WI almost always correlates with the angiomatous type of meningioma. -Heterogeneity is the rule because of the presence of cysts, vessels, or calcification. -Prominent pial blood vessel flow voids are frequent and provide evidence of the extra-axial nature of the tumor -CSF clefts around the margin of the tumor also confirm the extra-axial location -A key imaging feature is the broad dural base of these extra-axial masses (the “dural tail”). |
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What should you pay special attenuation to when evaluating a meningioma?
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Special attention should be given to possible involvement of the dural sinuses, as this finding is an important neurosurgical consideration. Any diminution in the caliber of a dural sinus adjacent to a meningioma is highly suspicious for involvement. Further evaluation with MR angiography or conventional angiography should be pursued to confirm this finding.
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Why does neuroIR get involved in treating meningiomas?
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Preoperative embolization of feeding vessels often facilitates neurosurgical resection.
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Classic finding of meningioma on angiography?
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-During the arterial phase, there is a radial arrangement of the vessels, with an early dense tumor blush that persists well into the venous phase.
-Enlarged dural vessels and arteriovenous shunting may be noted |
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What blood vessels typically supply meningiomas?
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-Meningeal branches, most commonly the middle meningeal artery, from the external carotid circulation are the primary supply to this tumor.
-The anterior meningeal artery (arising from the ophthalmic arteries) and posterior meningeal artery (arising from the vertebral arteries) also provide blood supply to these tumors. (notice that they are not supplied by circle of willis vessels) |
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What is a hemangiopericytoma?
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-Rare, arises from modified pericapillary smooth muscle cells.
-It looks like a meningioma, but unlike most meningiomas, the tumor is associated with an aggressive biologic behavior and a high recurrence rate and shows a predilection for late distant metastasis. -More likely to be multilobulated and exhibit bony destruction |
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What does a CNS met from lymphoma look like?
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It can look exactly like a meningioma
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How can a met be in the subdural space?
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Subdural lesions are believed to result from hematogenous spread
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How can pelvic cancers spread to the CNS?
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By way of the Batson venous plexus.
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What's the most common tumor in the atria of the lateral ventricles in an adult?
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The most common atrial mass in an adult is a meningioma.
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Where are ependymomas most commonly found?
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Ependymomas are most common in the fourth ventricle
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Which tumors tend to present in the anterior portion of the lateral ventricles? Which tumors tend to be in the posterior portion?
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Anterior and Body:
-Central neurocytomas -Subependymomas -Subependymal giant cell astrocytomas -Other astrocytomas Posterior: -Meningioma (most common) -Choroid plexus papilloma -Choroid plexus carcinoma -Metastasis |
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What entity likes the anterosuperior portion of the 3rd ventricle?
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Colloid cyst
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Differential for a mass in the lateral ventricles of a child?
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-Choroid plexus papilloma
-Primitive neuroectodermal tumor -Teratoma |
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Three reasons why a choroid plexus papilloma produces hydrocephalus:
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#1: Because of marked increase production of CSF by the tumor
#2: Impaired CSF resorption (secondary to tumoral hemorrhage) #3: CSF obstruction (secondary to the shear bulk of the mass). |
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Are choroid plexus papillomas benign or malignant?
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-The tumor is fairly bland from a biologic perspective and is regarded as a WHO grade I lesion.
-About 20% of cases occur as a choroid plexus carcinoma (WHO grade III), with the vast majority of these cases seen in young children. |
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What should you think of if you see calcification in the choroid plexus of a child (<10 years)?
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Choroid plexus papilloma
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What does a choroid plexus papilloma look like on CT?
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-Well-defined intraventricular mass that is isodense to hyperdense compared to normal brain and typically is multilobulated.
-These highly vascular tumors enhance markedly |
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What does a choroid plexus papilloma look like on MR?
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-On MR, they are isointense compared to gray matter on T1WIs and hyperintense compared to gray matter on T2WIs.
-These highly vascular tumors enhance markedly. |
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What would suggest that a choroid plexus papilloma has degenerated into a carcinoma?
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Carcinomatous degeneration is suggested by heterogeneity or parenchymal invasion into the adjacent brain.
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Prognosis for a choroid plexus papilloma?
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-The prognosis for a patient with a choroid plexus papilloma is quite favorable if the mass is resected early, before irreversible damage secondary to hydrocephalus or repeated hemorrhage has occurred.
-The prognosis for those with a choroid plexus carcinoma is more guarded. |
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What is a central neurocytoma? Where do they tend to occur?
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-Central neurocytoma is a tumor of neuroepithelial lineage arising from the septum pellucidum or the ventricular wall.
-Half of these originate in the lateral ventricle near the foramen of Monro and about 10% are bilateral. -Nearly 20% involve the third ventricle. -Rarely, they may arise elsewhere in the brain or spinal cord, in which case they are termed extraventricular central neurocytoma. |
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Differential for a tumor within the ventricular system of a young adult?
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-Subependymal giant cell astrocytoma
-Pilocytic astrocytoma -Ependymoma -Central neurocytoma |
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What do central neurocytomas look like on CT and MR?
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-Well-circumscribed lobulated mass within the lateral or third ventricles in most cases
-Overall hyperdensity is seen on CT, although cystic changes and calcification are both common. -On MR, the tumor is hyperintense on both T1WIs and T2WIs compared to white matter. -The areas of cystic change are typically numerous and give the mass a “Swiss cheese” morphology. -Enhancement is usually intense and diffuse on postcontrast imaging |
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So how can you tell a central neurocytoma from a choroid plexus papilloma from a subependymoma?
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They're pretty similar, but age helps you, because CPP's will be in kids while central neurocytomas will be in adults.
-Subependymomas will be in adults, and do not enhance as avidly as CPP's and central neurocytomas. |
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What does a subependymoma arise from? Are they benign or malignant?
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Immediately underneath the ependymal lining of the ventricular system lies a thin subependymal glial layer. A tumor that arises from this region is termed subependymoma and classified as WHO grade I.
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Where do subependymomas occur?
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Slightly more than half arise in the fourth ventricle, with about 45% located in the lateral ventricle
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What do subependymomas look like on CT and MR?
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-On CT and MR, the tumor manifests as a well-circumscribed lobulated intraventricular mass.
-It is usually isodense to hypodense on CT, with frequent calcification (33%) and cystic degeneration (20%). -Hypointensity on T1WIs and hyperintensity on T2WIs are seen on MR. -The vast majority show at least some enhancement, although generally the enhancement is not as diffuse as that seen in central neurocytoma. |
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What syndrome are subependymal giant cell astrocytomas associated with?
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-Subependymal giant cell astrocytoma has a strong association with tuberous sclerosis, occurring in up to 10% of patients.
-It is extremely rare in patients who do not have this syndrome. |
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What should you think if you see a mass in the foramen of Monro in a child?
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-Think of subependymal giant cell asatrocytoma
-Any mass discovered in the region of the foramen of Monro in a young patient should provoke investigation for other manifestations of tuberous sclerosis, including subependymal and cortical hamartomas. -Look for signs of hydrocephalus too! |
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What do subependymal giant cell astrocytomas look like on CT and MR?
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-On MR, it is typically isointense to slightly hyperintense to gray matter on T1WIs and hyperintense to gray matter on T2WIs, with some heterogeneity noted because of the calcification.
-Intense enhancement is the rule on postcontrast imaging (as opposed to subependymomas) |
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What would tell you a mass is a subependymoma vs. a subependymal giant cell astrocytoma?
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Location:
-Subependymomas are usually in the lateral or fourth ventricles. Supependymal giant cell astrocytomas are usually in the foramen of Monro -Also subependymomas do not enhance as avidly. |
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How do pts with a colloid cyst present?
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-The classic presentation is that of acute onset of a severe headache, which can be reproduced by the patient tilting the head forward (Brun phenomenon).
-Occasional fatalities have been reported. |
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What does a colloid cyst look like on CT and MR?
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-On CT, almost all are hyperdense to brain tissue.
-On MR, extremely variable signal intensity is seen on both T1WIs and T2WIs. -While rim enhancement has been seen in up to 40%, solid enhancement is definitely not a feature of this lesion and should provoke consideration of a different diagnosis. |
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What should you think of if you see solid enhancement of a colloid cyst?
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It's not a colloid cyst! Think of something else like:
-Meningioma -Choroid plexus papilloma -Hamartoma -Glioma -Vascular lesion -Granulomatous disease |
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Differential for a mass in the anterosuperior aspect of the third ventricle?
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-Colloid cyst
-Meningioma -Choroid plexus papilloma -Hamartoma -Glioma -Vascular lesion -Granulomatous disease |
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What kinds of tumors occur in the pineal region?
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-Germ cell tumors (most common)
-Pineoblastoma -Pineocytoma Less common: -Gliomas -Meningiomas -Arachnoid cyst -Vein of Galen aneurysm -Lipoma -Pineal cyst |
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How do pineal tumors differ by sex?
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A calcified pineal mass in a female patient is more likely to be secondary to a pineocytoma, whereas in a male patient, this same appearance is more likely to be caused by a germinoma.
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Pineal calcifications are seen all the time. When should you suspect a tumor?
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When calcification in the pineal region exceeds 1 cm in size, a pathologic pineal process should be suspected.
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Where do germ cell tumors occur in the brain?
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Pineal and suprasellar regions
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Symptoms of a germ cell tumor of the brain?
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-Clinical presentation is related to compression by the mass on the sylvian aqueduct, producing hydrocephalus, or to compression of the superior colliculus, producing Parinaud syndrome (paralysis of upward gaze).
-For those arising in the suprasellar region, symptoms related to hypothalamic dysfunction (emotional disturbance, diabetes insipidus, precocious puberty, etc.) and visual changes are common. |
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What do CNS germ cell tumors look like?
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-Germinomas typically manifest as an isodense to hyperdense well-circumscribed mass on CT.
-“Engulfment” of the normal physiologic calcification is a distinguishing feature of germinomas from the “exploded” appearance most commonly seen in pineal parenchymal tumors. -On MR, nonspecific hypointensity on T1WIs and hyperintensity on T2WIs is common. -Occasionally, hypointensity on a T2WI may be seen and favors a germinoma instead of a pineal parenchymal tumor. -Intense enhancement on either CT or MR is the rule |
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Types of CNS germ cell tumors?
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-Germinoma
-Teratoma -Embryonal carcinoma -Choriocarcinoma -Endodermal sinus tumor |
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What does a CNS teratoma look like?
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-Because it is composed of all three germ cell lines, it is usually extremely heterogeneous on CT and MR, with a mixture of fat, calcification, and cysts.
-Hydrocephalus is frequently noted and enhancement is variable. -Detection of a midline heterogeneous mass in a child should suggest this diagnosis. |
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What is a pineoblastoma? What does it look like?
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-PNET of the pineal gland
-The tumor is not well-circumscribed, often demonstrating a lobular contour, local invasion, and frequent calcification (all in contrast to a pineocytoma). -Intratumoral hemorrhage is rare (as opposed to other germ cell tumors in the pineal region). -Similar to other PNETs, CSF spread is common. -The tumor is highly malignant and classified as a WHO grade IV tumor. |
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What is trilateral retinoblastoma?
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Bilateral retinoblastoma in combo with a pineoblastoma
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What do pineal cysts look like?
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-Pineal cysts are common (about 40% in autopsy series) and have internal signal intensity similar to that of CSF.
-The lack of CSF pulsation may cause slightly higher signal on T1WIs and on T2WIs. -No enhancement of the cyst itself is seen and no internal architecture is noted. -Slight flattening of the superior colliculus may be seen, but the cysts do not cause Parinaud syndrome or hydrocephalus. -Intracystic hemorrhage is rare. |
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Most common sellar mass?
|
Pituitary adenoma
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Are most macroadenomas hormonally active?
|
No, microadenomas are most likely to be hormonally active
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Which types of pituitary adenomas are usually located laterally? Which are usually central?
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-Prolactinomas and growth hormone (GH)–secreting adenomas are more commonly located within the lateral aspects of the gland.
-Adenomas with secretion of adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone, or follicle-stimulating hormone/luteinizing hormone are more common in the central region of the gland. |
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What's the best sequence and projection to see pituitary microadenomas? What do they look like?
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-Microadenomas are usually best detected on coronal T1WIs as focal areas of hypointensity (on noncontrast studies) compared to the rest of the pituitary gland.
-Other associated features include deviation of the infundibulum, asymmetric convexity of the pituitary gland, and mild downsloping of the roof of the sphenoid sinus. -In general, administration of gadolinium contrast increases the conspicuity of these often small neoplasms, which are revealed as hypointense foci within the gland on immediate postcontrast scans or as hyperintense foci on delayed imaging (about 30 minutes postinjection). |
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How can you tell a pituitary macroadenoma from a craniopharyngioma or parasellar meningioma?
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-When they are heterogeneous because of cyst formation or hemorrhage, and differentiation from a craniopharyngioma or parasellar meningioma is difficult, the use of contrast may be helpful
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What's the difference between a Rathke cleft cyst and a craniopharyngioma?
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-Craniopharyngioma and Rathke cleft cyst arise from squamous epithelial remnants of the anterior lobe of the pituitary gland, with the craniopharyngiomas derived from the pars tuberalis and Rathke cleft cyst arising from the pars intermedia.
-However, whereas Rathke cleft cysts are usually asymptomatic (seen in up to 33% of autopsies), craniopharyngiomas are frequently symptomatic because of their larger size. -Compared to craniopharyngiomas, Rathke cleft cysts rarely show peripheral enhancement. |
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What do craniopharyngiomas look like on CT and MR?
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On CT, the classic appearance of a craniopharyngioma is a large cystlike sellar/suprasellar mass with an enhancing rim and evidence of some calcification.
-On MR, because of the presence of the liquid cholesterol, the classic finding of hyperintensity on T1WIs and T2WIs, corresponding to the cystic portion, is most common. -However, some craniopharyngiomas do not contain fluid but instead will have a solid nodule that may be completely calcified. -Enhancement of the rim and any soft tissue component is noted. |
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What do Rathke cleft cysts look like on CT and MR?
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-The cyst contents are variable.
-Most commonly, a mucoid fluid fills the cyst. Less commonly, serous fluid or desquamated cellular debris occupies the cyst. -Because of this variability, the cyst may be hyperintense on T1WIs and T2WIs, appearing identical to a craniopharyngioma, or it may be isointense to hypointense on either sequence because of cellular debris mimicking the appearance of a solid nodule. -Compared to craniopharyngiomas, Rathke cleft cysts rarely show peripheral enhancement. |
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Most common nerves affected by schwannomas?
|
They're most often associated with the vestibulocochlear (VIII) and trigeminal (V) nerves.
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General imaging characteristics of a schwannoma?
|
-On CT, schwannoma is usually isodense to hypodense.
-On MR, thin-section (<3-mm) axial and coronal T1WI images through the basal cisterns are ideal to exclude this neoplasm, which demonstrates hypointensity to gray matter on T1WIs and hyperintensity to gray matter on T2WIs. -Intense enhancement is seen on post-contrast images. -The larger a schwannoma is, the more likely it is to show heterogeneity because of cystic degeneration or hemorrhage. |
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What does a vestibular schwannoma look like?
|
-The tumor may be completely intracanalicular, or it may extend into the adjacent cerebellopontine cistern.
-Expansion of the canal is an imaging hallmark. -The single most helpful imaging feature is extension of the enhancement along the course of the seventh and eighth nerves, seen in about 80% of vestibular schwannomas |
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What could you confuse a vestibular schwannoma with? How do you tell the difference?
|
-Differentiation from a cerebellopontine meningioma may be difficult.
-The single most helpful imaging feature is extension of the enhancement along the course of the seventh and eighth nerves, seen in about 80% of vestibular schwannomas. -Meningiomas very rarely demonstrate this feature and frequently will have a “dural tail” |
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Mnemonic for suprasellar masses?
|
“SATCHMO”
-Sella (pituitary) tumor, Sarcoid -Aneurysm, Arachnoid cyst -Teratoma -Craniopharyngioma -Hypothalamic glioma, Hamartoma of tuber cinereum, Histiocytosis -Meningioma -Optic nerve glioma |
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What do trigeminal schwannomas look like?
|
-Trigeminal schwannoma can be identified by its location within the pontine cistern at the midpons level, between the trigeminal ganglion located in the Meckel cavity (just posterolateral to the cavernous sinus) and the brainstem.
-Extension through the ganglion and into the foramen ovale, foramen rotundum, or superior orbital fissure may be seen. -Intense enhancement |
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Compare and contrast schwannomas and neurofibromas:
|
-Schwannoma arises from Schwann cells that form the myelin sheaths of axons.
-The tumor is focal and encapsulated and affects the cranial nerves, most often the vestibulocochlear (VIII) and trigeminal (V) nerves. -Cystic degeneration is common, especially in larger lesions, and may be accompanied by hemorrhage in 5% of cases. -Neurofibroma, on the other hand, arises from fibroblasts and Schwann cells, is usually fusiform, and involves the cutaneous exiting spinal nerves. -It is rarely cystic or hemorrhagic. |
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Mnemonic for cerebellopontine angle masses?
|
"AMEN"
-Acoustic (vestibular) schwannoma (80%) -Meningioma (11%) -Ependymoma (4%) -Neuroepithelial cyst (arachnoid, epidermoid) |
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What are dermoid and epidermoid cysts? What are they composed of?
|
-Epidermoid and dermoid are uncommon congenital masses that result from enclosure of ectodermal elements when the neural tube closes.
-Both are benign and characterized by slow growth. -Epidermoids account for about 1% of all intracranial neoplasms, whereas dermoids, as intracranial masses, are much less common. -Both lesions are lined by squamous epithelium and produce large amounts of keratin. -The key histologic distinction between an epidermoid and a dermoid is that the dermoid contains a “pilosebaceous unit” (composed of skin, hair follicles, and dermal appendages), while the epidermoid does not. |
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Where are dermoid and epidermoid cysts usually located?
|
Epidermoids are most often located off the midline at the skull base (i.e., cerebellopontine cistern, parasellar, or the posterior fossa) while dermoids are characteristically midline masses, most common at the inferior vermis or at the vallecula.
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What do epidermoid cysts typically look like?
|
-They're located off-midline
-Epidermoids are well-circumscribed, lobulated soft tissue masses that, because of the presence of solid cholesterol and/or CSF within the interstices of the tumor, most commonly have signal intensities on both CT and MR that follow that of CSF (hypodense on CT, hypointense on T1WIs, and hyperintense on T2WIs) -Rim enhancement secondary to the presence of granulation tissue may be seen following contrast administration. -On occasion, epidermoids contain enough liquid cholesterol (similar to craniopharyngioma) to produce T1 shortening (hyperintensity) of the mass. |
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What could you confuse an epidermoid cyst with? How do you tell the difference?
|
-The primary differential diagnosis is an arachnoid cyst.
-DWI is very useful in distinguishing between these lesions, because the epidermoid is hyperintense compared to CSF, while the arachnoid cyst is isointense. |
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What do dermoid cysts typically look like?
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-Dermoids typically have signal characteristics that follow that of fat (low density on CT, hyperintense on T1WIs, with signal suppression on fat-suppressed images).
-They do not enhance unless infected. -Heterogeneity of the mass may be seen because of calcification and other soft tissue components. -The presence of a fat–fluid level is practically pathognomonic. -In the presence of an intracranial dermoid, the nasofrontal and occipital regions of the scalp should be evaluated to detect a sinus tract. |
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What could you confuse a dermoid cyst with? How do you tell the difference?
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-If no heterogeneity is present, it may be difficult to distinguish a dermoid from a lipoma.
-Lipomas are associated with blood vessels and cranial nerves. -The presence of either a flow void or a cranial nerve traversing the mass assures the diagnosis of a lipoma and effectively excludes a dermoid. |
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Complication of a dermoid cyst?
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Occasionally, dermoids may rupture into the subarachnoid space, producing chemical meningitis and manifesting as multiple foci of T1 shortening.
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What do intracranial lipomas look like?
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-They are most common in the interhemispheric falx (often associated with agenesis of the corpus callosum), quadrigeminal plate, and suprasellar regions.
-They have low density on CT but occasionally contain calcification. -On MR, they exhibit T1 hyperintensity, following the signal intensity of subcutaneous fat. -No enhancement is seen. -The presence of either chemical shift artifact or signal suppression on a fat-saturated T1WI establishes the diagnosis. -Lipomas are associated with blood vessels and cranial nerves. -The presence of either a flow void or a cranial nerve traversing the mass assures the diagnosis of a lipoma and effectively excludes a dermoid. |
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Why do arachnoid cysts form?
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-True arachnoid cysts are created by secretion of CSF from the cells lining the cyst and are therefore intra-arachnoidal.
-“Secondary” or “acquired arachnoid cysts” are in reality leptomeningeal cysts resulting from a prior inflammatory process (meningitis, hemorrhage, etc.). |
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Where are arachnoid cysts typically located?
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They are most commonly (50%) seen in the middle cranial fossa, where they may be quite large. Other sites include the frontal convexity, the suprasellar and quadrigeminal cisterns, and the posterior fossa. If they attain sufficient size to obstruct CSF flow or compress the brain, they may become symptomatic.
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What do arachnoid cysts look like?
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-Arachnoid cysts follow the attenuation/signal intensity pattern of CSF on CT and MR.
-Remodeling of the adjacent bone may be seen. -Hemorrhage may occur after trauma or spontaneously. -Unless infection is present, no enhancement is noted. -In contrast to the hyperintensity seen with epidermoids, arachnoid cysts do not show evidence of water restriction on DWI. |
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How do hamartomas of the tuber cinereum present?
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Hamartoma of the tuber cinereum is a rare congenital malformation of normal neuronal tissue in an abnormal location that is more common in boys presenting with precocious puberty, gelastic seizures, developmental delay, and hyperactivity.
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What do hamartomas of the tuber cinereum look like?
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-The mass is well circumscribed, round or oval in shape, and centered in the region of the tuber cinereum (at the base of the infundibulum).
-It does not calcify or hemorrhage. -On CT and MR, it has essentially the same signal intensity as brain tissue and does not enhance. -Along with the characteristic location, a stalk connecting the mass with the tuber cinereum or mamillary bodies cinches the diagnosis. |
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