CD99: A potential Diagnostic Marker for Differentiating Sub-ependymal Giant Cell Astrocytoma From Other Mimickers: A Report of Five Cases.

Background: Tuberous sclerosis (TSC) is inherited as an autosomal dominant disease, characterized by skin lesion and tubers in vital organs, especially brain in three categories including subependymal nodules, cortical tubers and subependymal giant cell astrocytoma. Subependymal giant cell astrocytoma (SEGA) is an indolent neoplasm which usually arises at the cauda thalamic groove near foramen monro, although it occurs usually in the clinical settings of TSC, a few number of SEGA has been reported without such history. Its morphology with special cytoarchitecture could be mistaken with other glial brain tumors with similar morphology. Therefore, investigating new markers for differentiating SEGA from other mimickers seems logical rather than other glioneural immunohistochemical markers introduced before.

Case studies: We investigated CD99 expression in SEGA as an adjunctive marker for diagnostic purposes. Five reported cases of SEGA were studied and all of them showed CD99 expression besides usual glioneural markers.

Conclusion: CD99 may be a useful adjunctive marker in differentiating SEGA from other mimickers.