NEURORADIOLOGY


 
Case 11 :  

A young male presents with seizures. 
What is the diagnosis?
 

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Imaging Findings reveal presence of cortical tubers and peri-ventricular calcification (sub-ependymal nodules)

Diagnosis
Tuberous Sclerosis

Discussion

Introduction
The phakomatoses is a unique group in which neurologic abnormalities are combined with congenital defects on the skin, retina and other organs. The term phakomatoses (Greek-phakos(lentil)) includes the major syndromes.

  1. Neurofibromatosis (Von Recklinghausen’s disease)
  2. Tuberous Sclerosis (Bourneville’s disease)
  3. Encephalo-trigeminal syndrome (Sturge-Weber)
  4. Cerebello haemangioblastomas (Von Hippel Lindau)

Recently, it has been suggested that “Ataxia telangiectasia” be included in this group of conditions.

Discussion
Tuberous sclerosis is classically characterized by the clinical triad of convulsive seizures, mental retardation and adenoma sebaceum. 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. The mutant gene is variably expressed in terms of severity and is associated with other phenotypic manifestations such as periungual and gingival fibromas, hypomelanotic cutaneous macules and multiple renal angiomyolipomas. A revised diagnostic criteria for tuberous sclerosis has been advocated consisting of major and minor criteria.

Major & Minor Criteria
Major 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 tuberous sclerosis.

Minor criteria include hypomelanotic macules, shagreen patches, gingival fibromas, renal cysts and cardiac rhabdomyomas.

Skin Changes
The skin changes include adenoma sebaceum, shagreen patches and multiple facial angiofibromas. Multiple facial angiofibromas are considered pathognomonic. While the complete clinical triad occurs in only 29% of patients, facial angiofibromas are present in 56%. Clinically, they are red, pink or flesh coloured papules or nodules with a smooth shiny surface. They are distributed symmetrically over the centrofacial area in a butterfly pattern on the face.

Complications
Death in tuberous sclerosis is due to renal failure due to renal angiomyolipoma or renal cysts or cardiac failure due to intra-cavitatory or intra-mural rhabdomyomas that may obstruct blood flow or produce cardiac arrhythmias.

Imaging Features
Prior to the advent of CT and MRI, the investigations available were plain radiographs and pneumoencephalography. Plain films demonstrated periventricular  calcification while pneumoencephalography demonstrated the characteristic “candle wax” pattern of nodular ependymal masses. CT scan and MRI can detect all the features of tuberous sclerosis namely, cortical tubers, astrocytomas and ventricular dilatation. CT reveals cortical tubers as hypodense, non-enhancing regions at the cortico-medullary junction or more diffusely affecting the white matter. MRI is more sensitive than CT for cortical tubers which are seen as focal areas hyperintense to brain parenchyma on T1 and hyperintense on T2; this area of abnormal intensity is due to dense gliosis and diminished myelin sheaths found in these cortical tubers. Roach and co-workers have found a correlation between the number of tubers seen on MRI and clinical severity.

Sub-ependymal 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. This can be picked up on MRI as hyperintense areas to brain on T2. Enhancement of these nodules on CECT is also seen as a sign of transformation.

Contribution
Dr. Ashok Raghavan, Manipal Hospital, Bangalore