Lipoma, cns

a rare congenital lesion characterized by the presence of fatty deposits in inappropriate places in the central nervous system. The most common sites are along the midline of the brain (corpus callosum, quadrigeminal cistern) or of the spine and spinal cord.

The embryological derangement that leads to the formation of lipomas is still debated; lipomas are variously considered to be the result of mesodermal inclusion due to dysraphism, hyperplasia of normal leptomeningeal fat cells, heterotopia of displaced dermal anlage or derivatives from the embryological meninx primitiva. This last hypothesis is seen nowadays as the most probable.

Spinal lipomas (see intradural lipoma) are distinct collections of fat and connective tissue that are at least partially encapsulated and have a definite connection with the spinal cord. Spinal lipomas are the most common type of occult spinal dysraphism and account for some 35% of skin-covered lumbosacral masses (Fig.1). Typically, the mass lies in the midline just cephalic to the intergluteal crease, and extends caudally, asymmetrically, into one buttock.

Intracranial lipomas may present as distinct masses of different size or as curvilinear shaped structures around the corpus callosum (Fig.2). Sometimes callosal lipomas may have intraventricular components within the choroid plexuses. The most common sites for intracranial lipomas are around the corpus callosum, in the quadrigeminal cistern, hypothalamic-suprasellar, the cerebellopontine angles.

Intracranial lipomas are usually asymptomatic and an occasional finding. They are, however, frequently associated with more severe congenital anomalies like corpus callosum agenesis, and may present with seizures, headache and behavioural disturbances.

CT clearly shows markedly hypodense structures in the characteristic sites. MR shows T1 hyperintensity and T2 hypointensity of fat and associated nervous anomalies when present.

GS