Fat and Cholesterol Containing Intracranial Lesions

1. Pat Farley, MD Neuroradiology Division, UNC Fat and Cholesterol Containing Intracranial Lesions

2. 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.

3. Dermoid Cyst • Unilocular cyst with thick walls of connective tissue • Rare • <0.5 % of intracranial tumors • Clinical Issues • Uncomplicated Dermoids: • Headache (30%) • Seizure (30%)

4. 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.

5. 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

6. 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

7. 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

8. Dermoid (large arrow, left) and fat droplets in SAS (arrows, right) are clearly seen.

9. 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

10. Dermoids, Angiography/MRA • Vasospasm may be present with rupture • Vessels encased by dermoid have an increased risk of rupture.

11. 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

12. 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.

13. Epidermoid in left CPA cistern is similar to CSF but not exactly like it. Note internal structures.

14. DWI shows high signal from this epidermoid in the left CPA cistern.

15. Epidermoid that could be confused with Dermoid • Rare variant • Uncommonly hyperintense to brain ("white epidermoid") due to high triglycerides & unsaturated fatty acids

16. 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.

17. Left middle cranial fossa arachnoid cyst shows no enhancement and no restricted diffusion on ADC map (right).

18. 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)

19. 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.

20. Nearly cystic craniopharyngioma in the suprasellar space.

21. 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)

22. 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

23. Teratoma • Midline mass • calcium, soft tissue, cysts, and fat • Locations: • Midline from optic chiasm to pineal gland • Supratentorial most commonly

24. Teratoma, CT • CT without contrast • Hyper, iso- and hypo-dense components of fat, fluid, soft tissue, and calcification • Post Contrast • Soft tissue components enhance

25. Teratoma, MRI • T1WI • Hyperintense signal from fat • Variable signal from calcium • MR helps characterizes relationship of teratoma to midline structures

26. Two examples of mature 3rd ventricular and suprasellar teratomas show cysts, solid components, and fat on non contrast studies.

27. Teratoma, Prognosis • Depends on size and location • Benign vs. Malignant • 5 year survival for malignant teratomas is 18%

28. Teratoma, Variant • Holocranial Teratoma in newborns • Be suspicious of it in a newborn with an intracranial mass replacing nearly all normal brain tissue.

29. 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)

30. 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

31. 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

32. Two examples of pericallosal lipomas. Left: nodular type with callosal agenesis. Right: tubular with normal corpus callosum.

33. 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

34. Lipomas, Morphology Interhemispheric lipomas • Curvilinear type • Thin, curves around CC body, splenium • Tubulonodular type • Bulky mass frequent calcification, usually associated with corpus callosal dysgenesis

35. 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

36. 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.

37. 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