A case of angioglioma composed of astrocytoma with a papillary growth pattern: Immunohistochemical and ultrastructural studies

We report a case of a large cystic astrocytoma associated with arteriovenous malformation in the right cerebral hemisphere of a 16-year-old boy. Neuroimaging showed large abnormal vessels with flow voids and arteriovenous shunt around the cystic lesion. Histologically, the cyst wall was formed by abnormal vasculature and clusters of glial cells forming a papillary growth pattern. The abnormal vasculature consisted of dilated vein-like vessels and medium-sized arteries with incomplete media, and was diagnosed as an arteriovenous malformation. Immunohistochemically, glial fibrillary acidic protein (GFAP) decorated both the perikaryon and the processes of the glial tumor cells. They were negative for epithelial membrane antigen (EMA), cytokeratin, and S-100 protein. Ultrastructurally, the tumor cells were rich in intermediate filaments, and neither cilia, microvilli, nor ependymal rosettes were verified. Based on these morphological features and the low MIB-1 labeling index of 0.8%, the glial tumor was diagnosed as astrocytoma, Grade II, according to the World Health Organization (WHO) tumor classification. An association of glioma with various types of vascular anomalies has been designated as angioglioma. A unique feature of the present case, however, is a papillary growth pattern, which is not listed in the current WHO classification of brain tumors. The recognition of the occurrence of such cases would be important in differential diagnosis of papillary ependymoma and choroid plexus papilloma.