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Neuroradiology Case of the Week

Case 286

Ashwani K. Sharma, MD and P-L Westesson, MD, PhD, DDS

Clinical Presentation: Patient is a 45-year-old male status-post total thyroidectomy. The patient presented with worsening of memory and cognitive problems. There is clinical suspicion of intracranial metastasis. MR of the head is done to evaluate for any metastasis.

Imaging Findings: Subependymal nodule (SEN) signal intensity on T2-weighted MR images varies from patient to patient but is typically hypointense because of the calcification. The appearance of subependymal giant cell astrocytoma (SEGA) on neuroimages closely resembles that of SENs, except that the tumors are larger and they enhance brightly after delivery of intravenous contrast agents. In addition, SEGAs are in variably located at the foramen of Monro.
     Advances in brain imaging have revealed that patients with TS often exhibit developmental anomalies that are not unique to the syndrome, such as agenesis of the corpus callosum, heterotopias, transmantle cortical dysplasia, and schizencephaly.
     Radial bands sometimes interconnect cortical tubers and SENs. These lesions are typically T1 hyperintense and T2 hypointense in infants and be come T1 hypointense and T2 hyperintense in older children and adults. Radial bands represent altered migration of neural progenitor cells from the ventricular germinal matrix to the cerebral cortex during brain development.

Diagnosis: Benign subependymal nodules

Discussion: The term "tuberous sclerosis" was first used in 1880 to describe a syndrome consisting of seizures, mental retardation and facial rash in a young girl. Tuberous sclerosis is the most common neurocutaneous syndrome after neurofibromatosis.
     Persons with the mild form of tuberous sclerosis can lead full lives without any loss of function. In others, disabilities can be severe, with seizures, infections, tumors, renal involvement or pulmonary complications causing significant mortality. The classic clinical triad of seizures, mental retardation and facial angiofibromas is present only in persons with more severe tuberous sclerosis.
     Tubers are benign lesions composed of dysmorphic neurons occupying a cortical or subcortical location. Subependymal nodules are composed of abnormal, swollen glial cells and bizarre multinucleated cells which are indeterminate for glial or neuronal origin. There is no interposed neural tissue. These nodules have a tendency to calcify as the patient ages. A nodule that markedly enhances and enlarges over time should be considered suspicious for transformation into a subependymal giant cell astrocytoma (SEGA).
     And like cortical tubers, SENs form early in brain development and are made up of highly disorganized and dysfunctional cells. However, while tubers have cells with both neuronal and glial characteristics, SENs are composed only of glial cells. SENs also differ from the relatively static tubers in that their growth can outpace that of the surrounding tissue, causing them to protrude into the cavities of the ventricles.
     Thus incidental detection of subependymal nodules raise suspicion of tuberous sclerosis gene in the family or it may be due to some mutation.

References:

1. Braffman BH, Bilaniuk LT, Zimmerman RA. MR of central nervous system neoplasia of the phakomatoses. Semin Roentgenol. 1990 Apr;25(2):198-217. [Medline]
2. Kingsley D, Kendall B, Fitz C. Tuberous sclerosis: a clinicoradiological evaluation of 110 cases with particular reference to atypical presentation. Neuroradiology. 1986;28(1):38-46. [Medline]
3. Braffman BH, Bilaniuk LT, Naidich TP, Altman NR, Post MJ, Quencer RM, Zimmerman RA, Brody BA. MR imaging of tuberous sclerosis: pathogenesis of this phakomatosis, use of gadopentetate dimeglumine, and literature review. Radiology. 1992 Apr;183(1):227-38. [Medline]