Specific Imaging Findings

Subependymal giant cell astrocytomas (SEGAs) almost exclusively originate from the subependymal surface of the caudate nucleus, near the foramen of Monro, in patients with tuberous sclerosis complex (TSC). Bilateral lesions are common; they are often asymmetric both in size and growth rate. SEGAs are prevailingly solid, although cystic components may be present, especially in large masses. Lesions may show lobulated margins and resemble a conglomeration of nodules. Calcification is common, and is best seen on CT. The solid component is isointense with gray matter on all MR imaging sequences, and enhances homogeneously with gadolinium administration. The lesions are similar to the brain on diffusion imaging. Diameter over 12 mm, or a lesion more than 5 mm in size with growth on serial imaging are the characteristics indicative of SEGA. All lesions at the foramen of Monro in TSC patients should be presumed to be SEGA until proven otherwise. Contrast enhancement was considered a differentiating feature of SEGA on CT; however, many subependymal nodules enhance on MRI.

Pertinent Clinical Information

SEGA is found predominantly during the first and second decades of life, sometimes even in utero. The lesion may be asymptomatic per se; however, when sufficiently large it may obstruct CSF flow at the foramen of Monro, leading to elevated intracranial pressure and hydrocephalus. Worsening of epilepsy may lead to neuroimaging and diagnosis of SEGA. Neurosurgical resection is an effective standard treatment and may be performed before the lesions become symptomatic; however, SEGAs frequently recur.