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24 Cards in this Set

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Internal auditory canal nerve arrangement
REMEMBER 7UP and Coke Down -- for the anterior aspect of the IAC.


Circle with 4 pie slices

Anterosuperior pie slice is 7

Anteroinferior pie slice is cochlear portion of 8


Posterosuperior slice is superior portion of vestibular nerve of 8


Posteroinferior is inferior portion of vestibular nerve of 8
CP angle mass
DDx is SAME


Schwannoma (8th, more commonly than 5th)


Aneurysm or Arachnoid cyst


Meningioma or mets


Epidermoid or ependymoma

and CPP
Ependymoma and CPP
Yes, they ARE located in the 4th ventricle when in the posterior fossa, but they can squirt out through the exit foramina and grow out there in the CP angle cistern
Vestibular schwannoma -- Where does it arise from usually?
Superior portion of vestibular nerve.


THE IMPORTANCE OF THIS IS THAT YOU CAN HAVE NERVE SPARING SURGERY THAT DOES NOT INTERFERE WITH THE 7th or Cochlear nerves


BUT ALSO REMEMBER THE FOLLOWING: AS THE NERVE COMES OFF OF THE CP ANGLE, IT IS STILL COVERED BY OLIGODENDROCYTES, NOT YET SCHWANN CELLS. THE SCHWANN CELL COVERAGE DOES NOT BEGIN UNTIL THE NERVE IS ALREADY IN THE IAC. THUS ALL VESTIB SCHWANNOMAS BEGIN IN THE IAC, AND THEN GROW BACK INTO THE CP ANGLE JUST BECAUSE THEY ARE FOLLOWING THE PATH OF LEAST RESISTANCE.

THEY ALWAYS START AS AN INTRACANALICULAR MASS
Most common CP angle mass
Vestibular schwannoma
Second most common CP angle mass
Trigeminal schwannoma
Third most common CP angle mass
Meningioma
Fourth most common?
Epidermoid inclusion cyst
Appearance of vestibular schwannoma that you are not used to
THEY CAN GET BIG

And when they do, they can dissect into the space between the pons and cerebellum and create a big mass there


ALSO, since they are just schwannomas, then like ALL schwannomas they have both Antoni A and B material, and so can have a very heterogeneous, even cystic apperarance. These cystic areas WILL NOT ENHANCE. Thus, while the solid portions will enhance very brightly, the liquid portions will NOT, so enhancement can be heterogeneous, and it is still a vestib schwannoma
CP angle mass, not coming from IAC
ASK FOR CT TO LOOK FOR HYPEROSTOSIS to rule in meningioma. Only lesion that will cause hyperostosis.

OR, look carefully on the MR at the medial margin of the petrous. It should be STRAIGHT. If it is heaped up at all, that is hyperostosis
Hint that lesion is a meningioma
HYPEROSTOSIS -- best sign


BROAD BASE of dural attachment. (IN CP ANGLE region this is along the medial surface of petrous bone)


Dural tail (non-specific)


Growing on both sides of falx, tentorium or into bone as well as brain
Meningioma mnemonic
4 H's


HYPEROSTOSIS


Homogeneous enhancement


Hemispheric


?
DDx for posterior fossa mass in child
4 things:


Ependymoma -- 4th ventricle


Medulloblastoma -- starts in vermis, extends into 4th ventricle


Pilocytic astrocytoma -- cerebellar hemispheric mass with cystic component


Brainstem glioma
Adult with posterior fossa mass (not in CP angle cistern)
Infarct or Hemorrhage


Mets


Hemangioblastoma


Ependymoma


Astrocytoma -- brainstem or cerebellar
Child with posterior fossa mass on CT
LOOK AT THE DENSITY

Medullos are SMALL ROUND BLUE CELL TUMORS, thus high nuclear to cytoplasmic ratio, and thus high attenuation values.
Location of 4th ventricle and vermis
4th ventricle is located just ANTERIOR to the cerebellar vermis
Mass in cerebellum in child with cystic and solid components
PILOCYTIC


Unlike a hemangioma, there is not much variability between the size of the solid and the size of the cystic components. The solid component is usually quite significant. So dont expect a cyst and a tiny mural nodule. The reason the hemangioblastoma can have a tiny mural nodule and a huge cyst is that the mural nodule in hemangioblastoma is very hypervascular and secretes lots of fluid.


Cystic component is not surrounded by enhancing tumor on all sides, i.e. it is not encased by solid elements. If it were, you would think tumor necrosis
Mass with cystic and solid components in 20 year old
Dilemma age, because could be either pilocytic or hemangioblastoma


DIFFERENTIATE THEM NOT BY SIZE OF CYST VERSUS NODULE, BUT BY THE DEGREE OF VASCULARITY OF THE NODULE. A VERY BRIGHT ENHANCING NODULE WILL BE HEMANGIOBLASTOMA, NOT PILOCYTIC.
Hemangioblastoma
MUST RULE OUT VHL


May be purely solid -- BRIGHT enhancement
Multiple bright enhancing solid homogeneous posterior fossa masses
Multiple hemangioblastomas of VHL

or

Mets
Hemangioblastoma in VHL
In a patient with VHL who has hx of RCCA, they are more likely to develop a PRIMARY HEMANGIOBLASTOMA than metastatic disease.

To tell the difference with more certainty? -- LOOK SUPRATENTORIALLY. If there is metastatic disease there, then its probably all mets. If not, then could likely be hemangioblastomas.
Mass conforming to 4th ventricle
Ependymoma. In the posterior fossa, ependymoma respects the boundaries of the 4th vent, but is still a bad tumor, because:


1) Early CSF dissemination -- these are the tumors that exude like toothpaste out of the outlet foramina


2) Start at floor of 4th ventricle, attached to brainstem.
Hypodense cerebellar mass on CT
Sure you can think of epidermoid, maybe even cystic portion of hemangioblastoma, but . . . DONT FORGET THE MOST COMMON THING LIKE YOU JUST DID . . . ITS INFARCT!!!!!!!!! INFARCT!!!!!
Mass in petrous apex
Cholesterol granuloma


Cholesteatoma


Glomus tumor


Endolymphatic sac tumor