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.
- Neurofibromatosis
(Von Recklinghausen’s disease)
- Tuberous
Sclerosis (Bourneville’s disease)
- Encephalo-trigeminal
syndrome (Sturge-Weber)
- 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
|
