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Intracranial lipoma

Intracranial lipomas are not a tumours as such, but rather a result of abnormal differentiation of embryologic meninx primitiva. They are frequently associated with abnormal development of adjacent structures. 

Epidemiology

Intracranial lipomas are congenital lesions and as such are found at any age when the brain is imaged for other reasons. 

Clinical presentation

They are usually asymptomatic, and either found incidentally or as a result of investigation of related malformations and their presentation (e.g. mental retardation, epilepsy, hydrocephalus etc...) 5-6.

Radiographic features

Intracranial lipomas are widely distributed in the intracranial compartment and although they can be found essentially anywhere, certain regions are characteristic and are discussed separately.

The characteristic finding on both CT and MRI is of a mass which has appearances consistent with fat. 

CT

Typically appears as a mass with uniform fat density (negative HU values). It has a lobulated 'soft' appearance, conforming to adjacent anatomy. No enhancement. Some peripheral calcification may be present. 

MRI

MRI with and without fat saturation are able to make the diagnosis easily. In the absence of fat saturated images, then chemical shift artefact may be useful. Signal characteristics are not surprisingly that of fat: 

  • T1: high signal intensity
  • T2: high signal intensity 
  • T1 C+ (Gd): no enhancement
  • fat saturated sequences: low signal 

Often the lipomas are traversed by cranial nerves and adjacent vessels, best seen on high resolution sequences. 

Treatment and prognosis

Intracranial lipomas are in most cases asymptomatic, and even when associated with symptomatic malformations (e.g. callosal dysgenesis) they usually require no treatment pe se. In fact attempts at resection have had relatively high morbidity with little benefit 5-6. Treatment of seizures or hydrocephalus is of course necessary if these are present 5-6

Differential diagnosis

The differential is essentialy that of masses which contain fat, and therefore includes:

On MRI, if no fat saturated sequences are available then a number of other possibilities should be entertained, which also have high T1 signal.

  • thrombosed berry aneurysm - often will have calcified rim, and haemosiderin staining on gradient echo / SWI sequences. 
  • white epidermoid - rare, and will restrict on DWI

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