Angiocentric glioma from a perspective of A-B-C classification of epilepsy associated tumors.

Angiocentric glioma (AG) is a newly-classified, very rare, WHO grade I central nervous system (CNS) lesion, occurring usually in children and young adults. Only 52 patients with AG have been reported so far, making it one of the rarest neuropathological entities. Hereby we present two new cases of AG in young subjects with detailed neuropathological investigations and a neuroradiological picture along with a brief summary of all already published literature reports of this tumor. Histopathological examination of the resected tissue from both cases revealed similar changes characteristic of AG. The tumors were composed of spindle-like, elongated cells, forming characteristic pseudorosettes around vessels and diffusively infiltrating surrounding tissue, trapping neurons between tumor cells. Noticeably, some neoplastic cells encrusting vessels extended far beyond the main tumor mass. Hypothetically, this may be responsible for the recurrence of the tumor even in the case of apparently total excision. In immunohistochemistry, AG cells were glial fibrillary acidic protein (GFAP) and vimentin positive, also exhibiting a strikingly significant epithelial membrane antigen (EMA) dot-like staining pattern. In one of the cases, electron microscopy revealed ependymal differentiation features such as microvilli and cilia. Taken together, all these data strongly confirm a dual astroglial-ependymal nature of the tumor. Follow up corroborates benign character of this neoplasm. Both AGs reported here were immunonegative for the product of the mutated IDH-1 gene what, according to our best knowledge, has never been reported so far. It may suggest that in their pathogenesis AGs differ from grade II astrocytomas, which in most cases harbor a mutation of IDH-1. Noteworthy, neuroimaging in our cases was relatively characteristic but not conclusive, therefore biopsy (at least) is mandatory. A newly proposed so called "A-B-C" classification of long-term epilepsy-associated tumors (LEATs) places AG in a category named ANET. The authors shortly review the A-B-C classification of LEATs.