fat containing lesions of the brain
TRANSCRIPT
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Fat and Cholesterol Containing Intracranial
Lesions
Pat Farley, MDNeuroradiology Division, UNC
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Objectives
• To name fat containing lesions of the brain.
• Give differentiators of these lesions.• Recognize associations and complications
of these lesions.• Recognize that dermoid and epidermoid
do not look alike, just sound alike.
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Dermoid Cyst
• Unilocular cyst with thick walls of connective tissue
• Rare– <0.5 % of intracranial tumors
• Clinical Issues– Uncomplicated Dermoids:
• Headache (30%)• Seizure (30%)
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Dermoids, Complications• Rupture
– This can cause a chemical meningitis as the fat droplets spread within the subarachnoid space with resultant inflammatory changes.
– Larger lesions are associated with higher risk of rupture.
• Transformation– Rarely can transform in to a malignant squamous cell
cancer.• Dermal sinus
– Can lead to infection.
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Dermoids, Imaging Appearance• Well-circumscribed lipid containing masses • Location
– Most often in sellar/parasellar/frontonasal region – Posterior fossa; midline vermis & 4th ventricle – May be intraventricular in lateral, 3rd, or 4th ventricles – May also be located in spine and orbits
• Ruptured Dermoid– Subarachnoid/intraventricular spread of fat contents
• Size– Variable
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Dermoids, CT Appearance• Non Contrast CT
– Classic• Round/lobulated, well-delineated, cystic mass • Fat hypodensity • 20% contain capsular calcifications • Rupture, droplets of fat disseminate in cisterns, may cause fat-fluid
level within ventricles – Atypical
• "dense" dermoid: Hyper attenuating on CT
• Skull/scalp dermoid expands diploic space • Frontonasal - Bifid crista galli, large foramen cecum with
possible sinus tract • Post Contrast - No enhancement
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Dermoids, MRI
• T1 and T2:– Hyperintense mass on T1WI. Heterogeneous
signal on T2.– Chemical shift artifact in frequency encoding
direction – Ruptured Dermoid
• Droplets very hyperintense on T1WI – Fat suppression sequence confirms – Fat-fluid level in cyst, ventricles common
– "dense" dermoid also hyperintense on T1WI
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Dermoid (large arrow, left) and fat droplets in SAS (arrows, right) are clearly seen.
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Dermoids, MRI with Contrast
• Unruptured– No enhancement
• Ruptured– Can have intense meningeal enhancement
secondary to chemical meningitis.
• MR Spectroscopy– Strong and broad resonances from mobile
lipids at 0.9 and 1.3 ppm
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Dermoids, Angiography/MRA
• Vasospasm may be present with rupture• Vessels encased by dermoid have an
increased risk of rupture.
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Dermoids, Prognosis/Therapy• Complete microsurgical excision
– Residual capsule may lead to recurrence – Rarely surgical remnants may degenerate in to
squamous cell cancer• Subarachnoid dissemination of contents may
occur during operative/postoperative course – Cause aseptic meningitis or other complications
(hydrocephalus, seizures, CN deficits) – Disseminated fat particles can remain silent without
neurologic changes
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Dermoid vs. Epidermoid• Epidermoid = congenital inclusion cyst• Usual appearance is similar to CSF
– Appearance is not identical to CSF however• FLAIR usually does not completely suppress• T1/T2 may be slightly off, CISS/FIESTA show internal structures• Diffusion restriction is key• Can see internal structures on CISS imaging
• Mass interdigitates in cisterns, and encases nerves and vessels.
• Most common differential for epidermoid is arachnoid cyst.
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Epidermoid in left CPA cistern is similar to CSF but not exactly like it. Note internal structures.
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DWI shows high signal from this epidermoid in the left CPA cistern.
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Epidermoid that could be confused with Dermoid
• Rare variant – Uncommonly hyperintense to brain ("white
epidermoid") due to high triglycerides & unsaturated fatty acids
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Epidermoid vs. Arachnoid Cyst
• Diffusion is key • Epidermoid is restricted• Arachnoid cyst is not
• Also epidermoids insinuate into adjacent tissues, arachnoid cysts tend to displace them.
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Left middle cranial fossa arachnoid cyst shows no enhancement and no restricted diffusion on ADC map (right).
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Craniopharyngioma
• Benign epithelial tumor derived from Rathke’s pouch epithelium
• Two Types:– Adamantinomatous type (classic)
• hyperintense cyst and heterogeneous nodule • More common in children (first age peak)
– Papillary type (more rare)• isointense solid component • More common in adults (second age peak)
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Imaging of Adamantinomatous Craniopharyngioma
• CT: Partially calcified, partially solid, cystic suprasellar mass
• MR :– T1 without Gd
• High signal intensity suprasellar mass on pre-contrast T1WI (protein, cholesterol, blood products in fluid)
– T1 with Gd:• Solid portions enhance heterogeneously, cyst walls
enhance strongly.
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Nearly cystic craniopharyngioma in the suprasellar space.
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Craniopharyngioma, Locations• Relation to Sella
– Suprasellar (75%) – Suprasellar and intrasellar components (21%) – Entirely intrasellar (4%)
• Often extend into multiple cranial fossae: Anterior (30%), middle (23%), posterior and/or retroclival (20%)
• Rare locations :– Optic chiasm, 3rd ventricle – Nasopharynx, pineal gland, sphenoid (sinus, clivus)
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Craniopharyngioma, Other Imaging Appearances
• Variable size– often large at presentation (> 5 cm)
• Effect on surrounding brain– Hyperintense signal in brain parenchyma
adjacent to tumor• Gliosis, tumor invasion, irritation from leaking cyst
fluid • Edema from compression of optic chiasm/tracts
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Teratoma
• Midline mass – calcium, soft tissue, cysts, and fat
• Locations:– Midline from optic chiasm to pineal gland – Supratentorial most commonly
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Teratoma, CT
• CT without contrast– Hyper, iso- and hypo-dense components of
fat, fluid, soft tissue, and calcification• Post Contrast
– Soft tissue components enhance
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Teratoma, MRI
• T1WI– Hyperintense signal from fat– Variable signal from calcium
• MR helps characterizes relationship of teratoma to midline structures
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Two examples of mature 3rd ventricular and suprasellar teratomas show cysts, solid components, and fat on non
contrast studies.
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Teratoma, Prognosis
• Depends on size and location• Benign vs. Malignant
– 5 year survival for malignant teratomas is 18%
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Teratoma, Variant
• Holocranial Teratoma in newborns
• Be suspicious of it in a newborn with an intracranial mass replacing nearly all normal brain tissue.
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Lipomas
• Mass made up of mature non-neoplastic adipose tissue
• Congenital malformations, not true neoplasm
• Arise from malformation of cells in primitive subarachnoid space (meninx primitiva)
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Lipomas, Location • Midline location common
– Supratentorial 80% • 40-50% interhemispheric fissure (over corpus callosum)
– may extend into lateral ventricles, choroid plexus • 15-20% suprasellar
– attached to infundibulum, hypothalamus • 10-15% pineal region
– usually attached to tectum • Uncommon
– Meckel cave, lateral cerebral fissures, middle cranial fossa – 20% infratentorial
• Cerebellopontine angle – may extend into IAC, vestibule
• Uncommonly in jugular foramen, foramen magnum
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Lipomas, Imaging
• CT– -50 to -100 H (fat density) – Calcification varies from none to extensive
• MRI– Hyperintense on T1WI – Hypointense with fat suppression – Striking chemical shift artifact on T2WI
• Enhancement– None
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Two examples of pericallosal lipomas. Left: nodular type with callosal agenesis. Right: tubular with normal corpus callosum.
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Lipomas, Vascular Imaging
• Angiographic Findings• Conventional
– ACA courses directly superiorly if CC agenesis present
– Arteries & veins often embedded within lipoma
• Similar findings may also be seen with MRA
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Lipomas, Morphology
Interhemispheric lipomas– Curvilinear type
• Thin, curves around CC body, splenium – Tubulonodular type
• Bulky mass frequent calcification, usually associated with corpus callosal dysgenesis
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Neoplasms with Fat
• Lipomatous differentiation/transformation of neoplasm– Neuroectodermal tumors
• PNETs, ependymoma, gliomas is rare
– Cerebellar liponeurocytoma • Mixed mesenchymal/neuroectodermal posterior fossa
neoplasm • Primarily hypointense on T1WI, mixed with hyperintense foci
with patchy, irregular enhancement
– Meningioma • lipomatous transformation is uncommon
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Lipomatous Transformation of Meningioma
• Mature adipocytes from metaplasia and meningioma or from production of triglycerides by cells
• Rare variant of meningioma • CT
– Heterogeneous with heterogeneous enhancement – Can mimic necrotic malignant tumors– Demonstration of fat attenuation suggests a benign
process but differential diagnosis of an extra-axial fat-containing tumor should include lipomatous meningioma.
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SummaryDermoid
– Hyperintense on T1 can be heterogeneous on T2. No enhancement.
• Lipoma– Hyperintense on T1, no enhancement, can have calcifications,
look for CC dysgenesis• Craniopharyngioma
– Contains hyperintense T1 cholesterol/blood products, soft tissue, cystic structures and calcification, enhances
• Teratoma– Contains hyperintense T1 fat, soft tissue, cystic structures and
calcification, enhances