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Intracranial lipoma


Synonyms
• Lipomatous hamartoma

Definitions

  • Mass of mature nonneoplastic adipose tissue 
  • CNS lipomas are congenital malformations, not true neoplasms
  • Lipoma variants in CNS include angiolipoma, hibernoma, osteolipoma


Diagnostic criteria 

  • Well-delineated lobulated extraaxial mass pial-based fatty mass that may encase vessels and cranial nerves with fat attenuation/intensity
  • Midline location common
  • 80% supratentorial
  • 40-50% interhemispheric fissure (over corpus callosum [CC]; may extend into lateral ventricles, choroid plexus)
  • 15-20% suprasellar (attached to infundibulum, hypothalamus)
  • 10-15% tectal region (usually inferior colliculus/superior vermis)
  • Uncommon: Meckel cave, lateral cerebral fissures, middle cranial fossa
  • 20% infratentorial : Cerebellopontine angle (may extend into internal auditory canal, vestibule)
  • Uncommon: Jugular foramen, foramen magnum
  • Varies from tiny to very large
  • CT: -50 to -100 Hounsfield units (HU) (fat density)
  • Ca++ varies from none to extensive .
  • Standard SE MR: Hyperintense on T1WI
  • Becomes hypointense with fat suppression
  • 2 kinds of interhemispheric lipoma


  1. – Curvilinear type (thin ICL curves around callosal body, splenium)
  2. – Tubulonodular type (bulky mass; frequent Ca++, usually associated with callosal agenesis)

TOP DIFFERENTIAL DIAGNOSES
• Teratoma
○ Locations similar to lipoma
○ Tissue from all 3 embryonic germ layers

DIAGNOSTIC CHECKLIST
• When in doubt, use fat-saturation sequence
• Could high signal on T1WI be due to other substances with short T1 (e.g., subacute hemorrhage)
• Beware: Lipoma can mimic intracranial air on NECT (use bone windows to distinguish)

• Best imaging tool
○ MR

• Protocol advice
○ Add fat-suppression sequence for confirmation

• Associated abnormalities
○ Most common: Interhemispheric lipoma with corpus callosum anomalies
○ Other congenital malformations: Cephaloceles, closed spinal dysraphism
○ Encephalocraniocutaneous lipomatosis → Fishman syndrome
○ Pai syndrome → facial clefts, skin lipomas; occasional ICLs, usually interhemispheric

DIAGNOSTIC CHECKLIST
Consider
• Could high signal on T1WI be due to other substances with short T1 (e.g., subacute hemorrhage)

Image Interpretation Pearls
• When in doubt, use fat-saturation sequence
• Beware: Lipoma can mimic intracranial air on NECT (use bone windows to distinguish)




Imaging gallery

Coronal graphic shows callosal agenesis with a bulky tubulonodular interhemispheric lipoma that encases the arteries and extends into the lateral ventricles. 


Sagittal T1WI MR shows a rather thin curvilinear interhemispheric lipoma in a 9 month old. Note that the hyperintense lipoma is thicker posteriorly than anteriorly. It wraps around the back of the corpus callosum and extends beneath the corpus into the velum interpositum.


Sagittal T1WI MR in a neonate shows a large, tubulonodular, interhemispheric lipoma dorsal to a wedge-shaped callosal remnant . The brain is otherwise normal. 



Axial T2WI FS MR in the same patient shows the lipoma as hypointense and lying between the 2 cerebral hemispheres. The lipoma extends through the choroidal fissures into the lateral ventricles  where it is in the stroma of the choroid plexuses.



Axial NECT in a young woman studied for an unrelated headache shows a hypodense linear structure in the midline. 



Sagittal T1WI MR in the previous patient shows that the linear structure st is a curvilinear interhemispheric lipoma that wraps around the posterior aspect of a hypogenetic corpus callosum and courses into the posterior part of the velum interpositum. The callosal genu and splenium are incompletely formed.



Sagittal T1WI MR in a 25-year-old man with unrelated symptoms shows a hypothalamic lipoma , which is located in the tuber cinereum of the hypothalamus (between the infundibulum and the mammillary bodies).


Sagittal T1WI MR shows a tectal lipoma  situated immediately posterior to the inferior tectum and between the inferior colliculus and the superior surface of the cerebellar vermis. This is a very common location for lipomas.



Axial T1WI MR shows a round lipoma  in the right cerebellopontine angle cistern, adjacent to the internal auditory canal (IAC). Lipomas do not cause hearing loss and should not be resected. 



Axial T1WI C+ FS MR shows that the mass  becomes very hypointense after the fat suppression pulse is applied. With fat signal suppressed, the 8th cranial nerve  can be seen coursing through the lipoma in the cerebellopontine angle cistern to the internal auditory canal.


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