Teaching Case

A 34-year-old female patient referred with headache and dizziness, lasting for a few months.

A 34-year-old female patient referred with headache and dizziness, lasting for a few months. An MRI study of the cranium was performed on a 1.5 T MR scanner, with SE T1, FSE T2, fat-suppressed SE T1-weighted sequences on three planes. The examination was found to be normal except a mass of quadrigeminal cistern, homogeneously hyperintense on T1 and T2-weighted sequences with loss of high signal on fat-suppressed T1-weighted sequence.

Intracranial lipomas are congenital malformations that result from persistence and abnormal differentiation of the meninx primitiva, a mesenchymal neural crest derivative which differentiates into pia mater, arachnoid, inner meningeal layer of dura mater. They are uncommon lesions accounting for 0.06 to 0.46% of all primary intracranial masses. The incidence of intracranial lipomas is neither age nor gender related. Microscopically they are composed of adipose tissue, with a variable mixture of vascular elements, musculo-collagenous fibers, glial and ganglion cells. They are located at or near the midline in 80-95 % of the cases. The locations for lipomas can be listed as pericallosal area (25-50%), sylvian fissure, quadrigeminal cistern, chiasmatic cistern, interpeduncular cistern, cerebellopontine angle cistern, cerebellomedullary cistern, tuber cinereum, choroid plexus of lateral ventricle. Intracranial lipomas are often asymptomatic and discovered incidentally. Seizures, headache, behavioral disturbances can be seen, but they are usually related to associated anomalies such as corpus callosum dysgenesis. Cranial nerve palsies occasionally occur with infratentorial lipomas due to localized mass effect of the lesions. Quadrigeminal cistern is a rare location for intracranial lipomas, they usually occur in isolation, but up to one third of the cases are associated with other congenital anomalies. They are characteristically hyperintense masses on T1 and less hyperintense masses on T2 weighted sequences with the cease of hyperintensity on fat-suppressed sequences on MRI. A more specific clue to the diagnosis of lipoma is the chemical shift artifact, which is simply related to the difference in resonant frequencies between fat and water protons. This artifact is displayed as a region of signal void at fat-water interfaces and hyperintensity at water-fat interfaces, along the frequency encoding axis.