Both of these patients have tuberous sclerosis, also known as Bourneville's Syndrome, an inherited autosomal dominant disease with variable penetrance. The characteristic clinical triad includes adenoma sebaceum of the face, seizures, and mental retardation. Numerous hamartomatous malformations are present, including renal angiomyolipomas (40-100%), cardiac rhabdomyomas (5-30%), and pulmonary lymphangiomyomatosis (less than 1%). Other central nervous system (CNS) abnormalities include cortical hamartomas or "tubers," white matter heterotopias, and subependymal tubers. The first patient shown above has developed one of the known complications of this disease, namely degeneration of one of the subependymal tubers into a giant cell astrocytoma at the foramen of Monro with secondary obstructive hydrocephalus. Histologically the subependymal nodules contain giant cells, mostly of the astrocytic type with deposits of calcium. They are located beneath the ependymal lining most commonly of the lateral ventricles posterior to the foramen of Monro, but occasionally of the third or fourth ventricle or the aqueduct of Sylvius. These nodules elevate the ependyma, resulting in protuberances into the ventricle described as a "candle guttering" type appearance. Calcification in these nodules was important for detection of these lesions with plain films or pneumoencephalography prior to the advent of CT. CT is helpful for detection of subependymal tubers primarily due to its sensitivity to calcium. Contrast enhancement of a subependymal tuber suggests degeneration into a giant cell astrocytoma since hamartomas or tubers do not enhance. The usual location for these slow growing astrocytomas is the foramen of Monro with secondary obstructive hydrocephalus, as in this example.

MR is more sensitive than CT for overall detection of intracranial abnormalities in tuberous sclerosis. Cortical and subcortical tubers, which are not visible on CT, can be identified on MR due to slight prolongation of T1 (darker) and T2 (brighter) compared to cortical gray matter. Hyperintense parenchymal lesions are the most characteristic abnormality on MR of tuberous sclerosis. Such findings were present in the younger of our two patients presented here. Within the white matter, radially oriented bands of increased signal on T2-weighted images correspond to groups of cells which are histologically identical to those within the cortical tubers.

Subependymal nodules have a slightly shorter T1 (brighter) and a slightly longer T2 (brighter) than cortical gray matter. However, tubers which have degenerated into giant cell astrocytomas have a significantly longer T1 and T2 than gray matter and markedly enhance on T1-weighted images after contrast administration. As with contrast CT, tubers do not enhance normally on MR. MR is insensitive for detection of small calcifications but is superior to CT for detection of cortical and subcortical lesions. MR or CT may be indicated for screening of subclinical disease in family members or for genetic counseling.