Specific Imaging Findings

Most intracranial lipomas occur at or near the midline, are very small and completely incidental. Large lipomas are most frequently pericallosal in location and are typically subdivided into tubulonodular and curvilinear types. Tubulonodular ones are bulky, usually situated anteriorly and associated with callosal agenesis or severe hypogenesis. Curvilinear lipomas are a thin ribbon of fat along the dorsum of the corpus callosum with extension around the splenium or a small retrosplenial button of fat and may be associated with splenial hypoplasia. Extension into the lateral ventricles is not uncommon. Other typical locations are quadrigeminal plate/superior cerebellar cistern and suprasellar/intrapeduncular cistern. On CT, lipomas are sharply marginated with markedly low density, usually below –40 HU. Central or peripheral calcification may be present. Ossification may also occur, particularly in suprasellar and interpeduncular lipomas. Lipomas are uniformly T1 hyperintense and maintain signal isointense to fat on all pulse sequences. Chemical shift artifact is observed around the edges and fat suppression sequences lead to complete signal dropout. Flow-voids of encased vessels may sometimes be present. Chemical shift artifact also allows for distinction of small lipomas from aneurysms on TOF MRA images.

Pertinent Clinical Information

The vast majority of lipomas are asymptomatic. Headaches, seizures, psychomotor retardation, and cranial nerve deficits have all been reported in association with intracranial lipomas. Sylvian fissure lipomas appear to be associated with epilepsy and hydrocephalus has been reported with quadrigeminal plate lipomas. Symptoms are usually due to associated malformations which are seen in over half of large lipomas and, in addition to callosal dysgenesis, include absence of septum pellucidum, vermian hypoplasia, aqueductal stenosis, and cortical malformations.