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Orbital ImagingMounir Bashour, M.D., C.M.

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What is required when you order orbital MR studies? 1. Surface coil (orbital or head coil) for

better visualization of structures of the orbit 2. Precontrast axial, coronal, and

sagittal T1 -weighted images 3. Axial, coronal T2-weighted images

(fast spin-echo sequences) 4. Postcontrast axial coronal T1 -

weighted images with fat suppression techniques

5. Sedation in children

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What is the strategy in ordering imaging studies in a child with the diagnosis of retinoblastoma? Diagnosis--Ca++ U/S +/- CT Scan Extraocular ext. -- MRI orbits Familial/Bilat --> MRI brain

(pinealoblastoma)

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What is the strategy in ordering imaging studies in an adult with the diagnosis of intraocular neoplasm? U/S IVFA/ICG MRI--fat suppression

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What are paramagnetic agents?

shorten the intrinsic T1 and T2 relaxation times

increase the signal intensity Melanin, methemoglobin, protein, and

gadolinium

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In which clinical situations are contrast-enhanced MR studies most helpful in the evaluation of a child with leukocoria?

To differentiate retinoblastoma from Coats' disease.

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In which clinical situations are contrast-enhanced MR studies most helpful in the eval-uation of an adult with vitreous hemorrhage? To differentiate a malignant melanoma of

the choroid from a hemorrhagic retinal detachment in age-related macular/extramacular degeneration.

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What are the indications for ordering CT orbital studies as a first choice? 1. Evaluation of orbital trauma 2. Detection of foreign body 3. Detection of calcification 4. Evaluation of osseous, cartilaginous,

and fibroosseous lesions 5. Evaluation of orbital soft tissue lesion

with suspicion of bony erosion or detection 6. Contraindication to MRI

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What are the indications for ordering MR orbital studies as a first choice? 1. Acute proptosis 2. Suspicion of optic nerve sheath

complex lesion 3. Intraocular tumor with

extraocular extension 4. Detection of wood foreign body 5. Contraindications to CT

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Name the most common orbital lesions showing a well-circumscribed and sharply delineated appearance on CT and MRI in kids 1. Dermoid cyst 2. Lymphangioma 3. Rhabdomyosarcoma 4. Optic nerve glioma

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Name the most common orbital lesions showing a well-circumscribed and sharply delineated appearance on CT and MRI in adults 1. Cavernous hemangioma 2. Neurofibroma 3. Neurilemoma 4. Fibrous histiocytoma 5. Lymphoproliferative disorders

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Name the most common orbital lesions showing an ill defined appearance on CT andMRI in children 1. Capillary hemangioma 2. Idiopathic orbital inflammation 3. Plexiform neurofibroma 4. Leukemic infiltrate 5. Eosinophilic granuloma

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Name the most common orbital lesions showing an ill defined appearance on CT andMRI in adults 1. Idiopathic orbital inflammation 2. Metastasis 3. Leukemic infiltrate 4. Primary malignant tumor 5. Lymphoproliferative disorders

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Which are the ocular and orbital tissues that do not normally enhance on postcontrast MR studies? 1. Lens 2. Vitreous 3. Sclera 4. Orbital fat 5. Optic nerve sheath complex

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In which clinical situation are contrast-enhanced MR studies most helpful in the evaluation of a patient with proptosis? Well circumscribed lesions

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What are the indications for MR angiography and carotid angiography when imaging orbital lesions?

None

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How can you differentiate optic nerve from optic nerve sheath lesions with CT and MR studies? MRI Normal nerve does not demonstrate any

enhancement Optic nerve tumor or inflammation

demonstrates central enhancement Optic nerve sheath neoplasm or inflammation

demonstrates peripheral enhancement A cystic or hemorrhagic lesion does not

enhance

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MR Features of Normal Ocular and Orbital Tissues