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102 Cards in this Set
- Front
- Back
What four major anatomic areas are used to subdivide the orbit when constructing a differential diagnosis?
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1. Globe
2. Optic Nerve and Sheath 3. Conal-Intraconal area 4. Extra-conal area |
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Along what scan plane is the orbit best imaged in the axial direction by CT or MRI?
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A plan along the anthropologic baseline or infraorbitomeatal line, because imaging in this plane closely parallels the orbital axis(permitting visualization of the optic nerve and horizontal eye muscles)
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The main portion of the triangular orbital room is comprised of the?(p 310-311 figure 14-1 and 14-2)
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Frontal bone, with the frontal sinus within
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The anterolateral part of the orbital roof forms a shallow fossa for the?
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Lacrimal gland
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The orbital roof can be imaged completely only in what plane(axial, sagittal, coronal)?
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Coronal
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What is the shape of the orbital floor?
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Triangular
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What bones form the floor of the orbit?
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1. Orbital plate of the maxilla
2. Orbital process of the palatine bone 3. Orbital surface of the Zygomatic bone |
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Where do inferior blowout fractures usually occur?
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Orbital plate of the maxilla, because it's quite thin
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Anterior aspect of the medial orbital wall is formed by?
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The frontal process of the maxillary bone(together with the lacrimal bone the frontal process of the maxillary bone forms the lacrimal fossa)
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What can mimic a medial orbital blowout fracture?
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Spontaneous dehiscence of the orbital flate occuring through the lamina papyracea into the ethmoid sinus.
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What forms the posterior portion of the medial orbital wall?
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A small portion of the sphenoid bone.
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Anteriorportion of the lateral orbital wall is formed by the?
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Orbital surface of the zygomatic bone.
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Where does the superior orbital fissure sit?
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At the margin between the lateral wall and orbital roof.
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The superior orbital fisure has what bone as its lateral and medial borders?
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Lateral border(greater wing of the sphenoid)
Medial border(lesser wing of the sphenoid) |
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Where does the medial tip of the superior orbital fissure lie?
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Beneath the optic canal
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How is the superior orbital fissure separated from the optic canal?
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By the optic strut
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What is the optic strut?
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A bridge of bone formed by the lesser wing of the spenoid, separates the superior orbital fissure from the optic canal.
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Superior orbital fissure contents(3)
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1. Superior ophthalmic vein.
2. CN III, CN IV, CN VI 3. V1(Ophthalmic portion trigeminal) |
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What can the superior orbital fissure be a conduit for?
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for inflammatory or neoplastic dz between the orbital apex and cavernous sinus(intracranial structure)
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Where is the inferior orbital fissure?
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Between the floor and lateral wall of the orbit.
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What does the inferior orbital fissure connect with?
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The pterygopalatine fossa and nasopharyngeal masticator space(intfratemporal fossa) inferolaterally
- Deep face inflammatory and neoplastic lesions can gain access to the orbital apex) |
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Contents of the inferior orbital fissure?
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Infraorbital and zygomatic nerves
Nerves from pterygopalatine ganglion Venous connections between inferior opththalmic vein and pterygoid plexus |
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What is the optic canal formed by?
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Completely formed by the lesser wing of the sphenoid.
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The optic canal contains?
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Optic Nerve
Ophthalmic artery (both of which are contained in a dural sheath) |
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The sphere of the globe is divided into the anterior and posterior segments by?
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The lens
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Three segments of the Optic nerve sheath
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1. Orbital
2. Canalicular 3. Intracranial |
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How long is the optic nerve?
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4.5 cm, with the orbital segment is the longest
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What is the ring of Zinn?
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Tendinous ring that encloses the central portion of the superior orbital fissure and optic foramen made up of the 4 rectus muscles
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What passes through the ring of Zinn?
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Optic nerve/sheath complex,
Ophthalmic artery Distal aspects of CN III and VI |
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Where does the superior ophthalmic vein exit the orbit?
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Through he superior orbital fissure.
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What is contained in the extraconal region(between the muscle cone and bony orbit?
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Only fat and the lacrimal gland.
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Describe the lacrimbal gland
(shape/location) |
lens-shaped organ located in the anterior orbit superolateral to the globe.
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Definition of microphthalmia.
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Congenital underdevelopment or acquired diminution in the size of the globe.
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What diseases can you see bilateral micropthalmia in younger patients?
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Congenital rubella
Persistent hyperplastic vitreous Retinopathy of prematurity Retinal folds Lowe Syndrome |
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What diseases can you see bilateral micropthalmia in older patients?
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Trauma
Surgery Inflammation with disorganization of the eye(phthisis bulbi) |
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Congenital vs. acquired micropthalmia - radiologic characteristics
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Congenital - small globe associated with a small, poorly developed bony orbit
Acquired (normal orbit, shrunken, calcified globe) |
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Macrophthalmia definition
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Enlargement of the globe.
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Causes of Macrophthalmia
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Juvenile glaucoma or myopia
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Definition of Coloboma
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Congenital defect in the globe, usually at the point of insertion of the optic nerve.
(represents a localized defect in the sclera, uvea, and retina) |
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What does a CT/MR show in coloboma?
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a small globe with a cystic outpouching of vitreous at the sate of attachment of the optic nerve to the globe
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Clinical presentation of hyperplastic primary vitreous?
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Unilateral leukokoria in male infants, which may simulate retinoblastoma.
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Pathologic features of hyperplastic primary vitreous
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1. Persistecne of primary vascular vitreous which normally undergoes involution by the sixth embryonic month.
2. Hyperplasia of the residual embryonic connective tissue occurs after involution |
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Persistent hyperplastic primary features?
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- Microphthalmic globe with enhancing, increased density in the vitreous humor
- a tissue density band may extend from the back of the lens to the posterior inner surface of the globe. |
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Retinopathy of Prematurity - patholigic features?
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abnormal proliferation of retinal vascular buds, often a/w use of high concentrations of oxygen for premature infants in neonatal ICUs(due to long term vent support)
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Retinopathy of prematurity
(Radiologic features) |
Increased density in the vitreous bilaterally
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Coat's dx (clinical presentation)
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Unilateral leukokoria in a 6-8 year old boy.
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Coat's dx (pathologic feature)
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Congenital vascular malformation of the retinal characterized by multiple telangiectatic vessels
- leakage of serous and lipoproteinaceous exudate from these vessels cause retinal detachment. |
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Coat's disease(radiologic characteristics)
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- Increased density in part or all of the vitreous of the globe
- normal globe size and lack of calcification. - can appear identical to persistent hyperplastic vitreous or retinopathy of prematurity. |
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Scleritis - pathologic features
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Idiopathic scleral inflammation or associated with systemic disease
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Scleritis(CT/MRI)
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Thickened, enhancing sclera is seen on enhanced CT or MR
-Choroidal detachment may be associated |
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What is the most common tumor of the globe during childhood?
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Retinoblastoma
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Retinoblastomas, what percentage is unilateral vs. bilateral
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75% unilateral
25% bilateral |
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Why is CT the preferred method for evaluating leukocoria?
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Because of it's sensitivity to calcification
MRI is used when further delieation of the extraocular extent of the tumor is required. |
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What does a CT scan show in retinoblastoma?
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An intraocular mass with calcification in patient younger than three
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What if you see bilateral retinoblastoma and a pinealoma, what is it called?
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Trilateral retinoblastoma.
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What is the most common primary intraocular malignancy in adults?
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Uveal melanoma.
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Is CT/MR routhinely used in uveal melanoma dx?
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no, clinical-ultrasound diagnosis is made confidently.
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CT features of uveal melanoma
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ST mass adjacent to the outer layer of the globe that bulges inward toward the vitreous
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MR freatures of uveal melanoma
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Sharply circumscribed lesion with high signal on T1 weighted images d/t paramagnetic properties of melanin
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What are the most common lesions that metastasize to the globe?
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Lung
Breast |
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Where does metastatic tumor to the globe most commonly involve?
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The uveal tract(ie. vascular layer between the retina and sclera)
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Ocular mets - CT characteristics
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Thickened areas o increased density
- usally in the posterior temporal portion of the uveal tract near the macula(an area of rich vascular supply) |
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Choroidal hemangioma is associated with what syndrome?
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Sturge Weber syndrome
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Choroidal hemangioma - CT pathologic/radiographic features
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-Benign vascular lesion that can mimic more ominous intraocular masses
- on CT its a lenticular to flat, intensely enhancing ocular wall mass. |
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Why is a CT/mri order in patient with a hypoplastic optic nerve?
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To exclude the possibility of an intraorbital or intracranial lesion affecting the visual pathway.
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Major Differential diagnostic considerations in a child with leukocoria?
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Toxocara endopthalmitis
Persistent hyperplastic vitreous Retinopathy of prematurity Coat's (calcs are rare in these diseases, unlike retinoblastoma) |
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Septo-optic dysplasia syndrome features?
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Bilateral or unulateral optic nerve hypoplasia
Absence of septum pellucidum Dysplastic 3rd ventricle Hypothalamic hypituitarism Growth hormone deficiency. |
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Causes of optic neuritis?
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MS
pseudotumor Sarcoidosis XRT Viral Tuberculous Syphilitic neuritis |
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What are the two common tumors of the optic nerve/sheath complex?
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Optic nerve glioma
Optic nerve/sheath meningioma |
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Who usually presents with optic gliomas?
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- Children within their first 10 years of life
- could also have hypthalamic disorder and obstructive hydrocephalus(signals the presence of a larger tumor with intracranial extension) |
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Optic nerve gliomas associated with what syndrome?
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NF I (1/3 of patients have NF1)
Conversely(15% of NF patients have optic nerve glioma) |
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Intracranial extension of an optic glioma, compare and contrast from an optic nerve sheath meningioma.
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an optic nerve glioma extension intracranially along the optic pathyway
- optic nerve meningioma, if intracranial extension occurs, it extends only a short distance along the prechiasmatic optc nerve sheath |
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Calcifications - optic nerve gliomas vs optic nerve meningiomas
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Optic nerve gliomas - non calcified
Optic nerve meningiomas - Have calcifications |
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Optic nerve sheath meningioma
(clinical presentation) |
Middle aged women
Children with NF II |
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Optic nerve glioma, high or low grade
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in childhood, optic nerve gloma is most commonly a low grade malignancy of the pilocytic astrocytoma variety.
in adulthood, its more aggressive like glioblastoma |
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Optic nerve meningioma features?
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- Marked contrast enhancement
- Enhancing tumor around the nonenhancing nerve results in a "tram track" appearance on axial images |
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What is the most common cause of an intraorbital mass lesion in adults?
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Pseudotumor
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Pseudotumor may be seen in association with?
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Wegener's granulomatosis
Fibrosising mediastinitis Thyroiditis Cholangitis |
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Pseudotumor - biopsy of the involved orbital area reveals?
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- Lymphocytic infiltrate, may have a variable histologic appearance
- later in the disease fibrosis and collagen fibers appear in the pathologic specimen. |
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Orbital pseudotumor involves which structures within the orbit?
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Retrobulbar fat(76%)
Extraocular muscle or muscles(57% Optic nerve(38%) Uveal-scleral area(33%) Lacrimal gland(5%) |
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What are the two principal pseudotumor types?
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Tumefactive(ie, diffuse involvement of conal and intraconal structures)
Myositic(involving the extraocular muscles) |
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Tumefactive type of tumor must be differentiaed from what? How?
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True orbital tumor
Clinical presentation and response to steroids dictate the need for biopsy |
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The myositic type of pseudotumor must be differentiated from?
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Thyroid Ophthalmopathy
-unilateral involvement of a single extraocular muscle including the tendinous insertions is highly suggestive) |
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What is the most common cause of unilateral or bilateral exophthalmos in adults?
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Thyroid ophthalmopathy
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Thyroid ophthalmopathy versus myositic pseudotumor on CT?
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Thyroid opthalmopathy has EOM enlargement and spares the tendinous attachments to the globe
-Pseudotumor - enlarged EOMS and involves the tendinous attachements |
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Carotid cavernous fistula - pathology
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Spontaneous or post-traumatic communication between the cavernous carotid artery and cavernous sinus
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Carotid cavernous fistular - radiology
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Engorgement of the superior ophthalmic vein and EOMs.
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Venous varix - pathologic features?
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An enormously dilated vein of either congestive or acquired orignin
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Venous varix - CT
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Lobulated densely enhancing intraconal structure that enlarges with valsalva
- may see phleboliths |
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Superior ophthalmic vein thrombosis?
clinical presentation? |
- occurs in conjuction with cavernous sinus thrombosis
- Subsequent dysfunction of CN III, IV, and VI |
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What is the most common orbital tumor?
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cavernous hemangioma
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Cavernous hemangioma on CT?
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Intraconal sharply circumscribed, rounded, dense mass that often spares the orbital apex
- uniform enhancement is the rule - bone destruction never occures(but may cause bone deformity) |
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At what age to cavernous hemangiomas present?
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20-40
unilateral proptosis with diplopia and diminution of vision resulting from optic nerve compression by tumor |
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Who gets capillary hemangiomas?
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infant(<1 year) with proptosis and swelling of eyelid and conjunctive that increases with crying or Valsalva
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Most common causes of proptosis?
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Oribital pseudotumor
Cavernous hemangyioma Oribital lymphoma(3rd most common cause) |
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Technically speaking, the extraconal region is comprised of?
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only the lacrimal gland and fat.
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Most acute enlargement of the lacrimal gland is due to?
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inflammatory enlargement in younger patients resulting from postviral syndrome
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Chronic lacrimal gland inflammation is secondary to(3)?
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Sjogren's Syndrome
Mikulicz's syndrome Sarcoidosis |
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What is Mikulicz's syndrome?
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Nonspecific enlargement of the lacrimal and salivary glands associated with sarcoidosis, lymphoma, or leukemia
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What two epithelial tumors account for 50% of all lacrimal gland tumors?
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Benitgn mixed ttumor
Adenoid cystic carcinoma |
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Whewre is non-hodgkin lympihoma of the orit most frequently found?
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in the lacrimal gland
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What is the most commmon meningioma in the extraconal area?
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Spenoid wing meningioma.
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