|Case 6 : (MRI)|
MR scan shows hyperintense subependymal nodules along both lateral ventricles, these appear hypointense on T2WI. On T1WI, similar hyperintense strands are seen radiating from peri-ventricular region to cortex.
The clinical triad of convulsive seizures, mental retardation and adenoma sebaceum characterizes tuberous sclerosis (TS). It is a disease of dominant inheritance with variable expressivity and high penetrance due to a mutant gene situated in the long arm of chromosome 9.
A revised diagnostic criteria for tuberous sclerosis has been advocated consisting of major and minor criteria:
Include facial angiofibromas, fibrous plaques on the forehead and scalp, cortical tubers, subependymal glial nodules, and multiple renal angiomyolipomas. Out of these, only one is required for the diagnosis of TS.
Hypomelanotic macules, shagreen patches, gingival fibromas, renal cysts and cardiac rhabdomyomas.
The skin changes include adenoma sebaceum (actually a misnomer, since the major histological changes in angiofibromas are dermal fibrosis and vascular dilatation, since sebaceous glands are not a significant component of the skin lesions and are usually atrophic), shagreen patches and multiple facial angiofibromas.
Other common findings include astrocytic hamartoma of the retina or the optic nerve, pedunculated white/ gray tumors of the conjunctiva or cornea, papillodema which may be secondary to a brain tumor, glaucoma and nystagmus, pulmonary lymphangiomatosis, osteosclerosis of the calvarium and splenic and hepatic hamartomas.
Death in TS is due to renal failure due to renal angiomyolipoma or renal cysts or cardiac failure due to intra-cavitatory rhabdomyomas that may obstruct blood flow or produce cardiac arrthymias.
CT and MR imaging can detect all features of TS, namely cortical tubers, astrocytomas and ventricular dilatation. CT reveals cortical tubers as hypodense, non-enhancing lesions at the cortico-medullary junction or more diffusely affecting the white matter. MR is more sensitive than CT for cortical tubers which are seen as focal areas hyperintense to brain parenchyma on T1, this area of abnormal intensity is due to dense gliosis and diminished myelin sheaths found in these cortical tubers. More specifically, MR may reveal hyperintense bands in the white matter on long TR sequences that are radially oriented, and this confirms to clusters of heterotopic giant cells; Roach & co-workers have found a correlation between the number of cortical tubers and clinical severity.
Subependymal nodules occur on the surface of the caudate nucleus, more often on the lamina of the sulcus thalamo-striatus just posterior to the foramen of Monro. Their transformation to giant cell astrocytomas is seen in 1.7-10% cases.
Dr. Deepak Patkar, MRI Nanavati Hospital, Mumbai.