Fat and Cholesterol Containing Intracranial Lesions Pat Farley, MD Neuroradiology Division, UNC 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. Dermoid Cyst Unilocular cyst with thick walls of connective tissue Rare <0.5 % of intracranial tumors Clinical Issues
Uncomplicated Dermoids: Headache (30%) Seizure (30%) 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. 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 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 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 Dermoid (large arrow, left) and fat droplets in SAS (arrows, right) are clearly seen. 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
Dermoids, Angiography/MRA Vasospasm may be present with rupture Vessels encased by dermoid have an increased risk of rupture. 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 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. Epidermoid in left CPA cistern is similar to CSF but not exactly like it. Note internal structures. DWI shows high signal from this epidermoid in the left CPA cistern.
Epidermoid that could be confused with Dermoid Rare variant Uncommonly hyperintense to brain ("white epidermoid") due to high triglycerides & unsaturated fatty acids 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. Left middle cranial fossa arachnoid cyst shows no enhancement and no restricted diffusion on ADC map (right). Craniopharyngioma Benign epithelial tumor derived from Rathkes 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) 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.
Nearly cystic craniopharyngioma in the suprasellar space. 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) 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 Teratoma Midline mass calcium, soft tissue, cysts, and fat Locations: Midline from optic chiasm to pineal gland
Supratentorial most commonly Teratoma, CT CT without contrast Hyper, iso- and hypo-dense components of fat, fluid, soft tissue, and calcification Post Contrast Soft tissue components enhance Teratoma, MRI
T1WI Hyperintense signal from fat Variable signal from calcium MR helps characterizes relationship of teratoma to midline structures Two examples of mature 3rd ventricular and suprasellar teratomas show cysts, solid components, and fat on non contrast studies.
Teratoma, Prognosis Depends on size and location Benign vs. Malignant 5 year survival for malignant teratomas is 18% Teratoma, Variant Holocranial Teratoma in newborns Be suspicious of it in a newborn with an
intracranial mass replacing nearly all normal brain tissue. 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) 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
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 Two examples of pericallosal lipomas. Left: nodular type with callosal agenesis. Right: tubular with normal corpus callosum. 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 Lipomas, Morphology Interhemispheric lipomas Curvilinear type Thin, curves around CC body, splenium Tubulonodular type
Bulky mass frequent calcification, usually associated with corpus callosal dysgenesis 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 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 fatcontaining tumor should include lipomatous meningioma. Summary Dermoid
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
