Neuroradiology

Subependymal hamartoma

(also called subependymal nodule), one of the CNS manifestation of tuberous sclerosis. They are defined as small, round lesions originating from the wall of the lateral ventricles and protruding into the ventricular lumen. Histology shows that they are composed of bizarre giant glioneuronal cells, similarly to cortical hamartomas.

When greater than 12 mm in size or if located near the foramen of Monro, possibly causing hydrocephalus, they are suggestive of subependymal giant cell astrocytomas.

Subependymal nodules frequently calcify after the age of 2 years so that they can be seen on plain film radiographs and can be nicely documented by CT. On MR images they appear as irregular round or oval masses projecting into the CSF-filled ventricles. They change with respect to MR signal intensity over time: T1 hyperintense, with respect to the unmyelinated white matter, and T2 isohypointense in neonates and younger children, T1 isointense and variably T2 hypointense, depending upon the extent of calcification, in older patients. They have a variable pattern of enhancement (ranging between 30 - 80%) which is not necessarily a sign of conversion into a neoplasm, i.e. subependymal giant cell astrocytoma.

 

NC