Anaplastic astrocytoma with angiocentric ependymal differentiation.

Angiocentric glioma (AG) is an epileptogenic benign cerebral tumor primarily affecting children and young adults, and characterized histopathologically by an angiocentric pattern of growth of monomorphous bipolar cells with features of ependymal differentiation (WHO grade I). We report an unusual cerebral glial tumor in a 66-year-old woman with generalized tonic-clonic seizure; the patient also had a 6-year history of headache. On MRI, the tumor appeared as a large T2-hyperintense lesion involving the right insular gyri-anterior temporal lobe, with post-contrast enhancement in the insula region. Histopathologically, the tumor involving the insular cortex-subcortical white matter was composed of GFAP-positive glial cells showing two different morphologies: one type had monomorphous bipolar cytoplasm and was angiocentric with circumferential alignment to the blood vessels, with dot-like structures positive for epithelial membrane antigen and a Ki-67 labeling index of <1%, and the other was apparently astrocytic, being diffusely and more widely distributed in the parenchyma, showing mitoses and a Ki-67 labeling index of >5%. In the anterior temporal lobe, a diffuse increase in the number of astrocytic cells was evident in part of the cortex and subcortical white matter. On the basis of these findings, we considered whether the present tumor may represent an unusual example of AG with infiltrating astrocytic cells showing primary anaplastic features (AG with anaplastic features), or anaplastic astrocytoma showing primary vascular-associated ependymal differentiation (anaplastic astrocytoma with angiocentric ependymal differentiation). At present, the latter appears to be the more appropriate interpretation.