DIAGNOSIS Angiocentric glioma in the hippocampus
Angiocentric glioma (AG) is newly described as a novel epilepsy-associated tumor in the 2007 WHO central nervous system (CNS) tumor classification. There were only 28 cases in 4 papers that have been reported in the Pubmed literature till now[1,2,4,5]. Most of these patients were youngsters with drug-resistant epilepsies in the cortex. Genetic analyses on this new tumor entity have not been performed so far because of small number of cases. Lellouch-Tubiana et al reported the presence of a neuronal cell component in all cases of their series and thus classified this tumor type as a mixed glioneuronal neoplasm. Wang et alproposed the term monomorphous angiocentric glioma, whereas Lellouch-Tubiana used the term angiocentric neuroepithelial tumor. In the new edition of the World Health Organization (WHO) classification of tumors of the nervous system, the tumor be included under the designation of ''angiocentric glioma'' as new distinct tumor entity. Given the uncertainties regarding histogenesis, angiocentric glioma was grouped with astroblastoma and chordoid glioma of the third ventricle in the category of 'Other neuroepithelial tumors', previously designated 'Tumors of uncertain origin'. Due to its benign clinical behavior and the possibility of curative surgery, the neoplasm was assigned to WHO grade I. All patients in previous reports presented with intractable focal epilepsy in childhood. The age at surgery was later, ranged from 2.3 to 70 years (mean 17years).
Angiocentric gliomas are located superficially. The most common sites being the fronto-parietal cortex and the temporal lobe as well as the hippocampal region. MRI demonstrates a well delineated solid, hyperintense, non-enhancing cortical lesion with extension into the subcortical or adjacent ventricle. Hyperintensities in T1-weighted images and mixed signals in T2-weighted are the characteristics of an AG. Necrosis and calcification are rare. Histologically, well-developed perivascular pseudorosettes can be seen in most cases. The bipolar spindled cells arranged about cortical blood vessels in mono-multilayered sleeves that extend lengthwise along vascular axes and as radial pseudorosettes with an ependymomatous appearance. Mitoses are rare. Complex microvascular proliferation and necrosis were not observed. Immunohistochemistry, for GFAP, S-100, and vimentin are positive while Syn, CgA, NeuN and P53 are negative. EMA expression shows a "dot-like" pattern in the cytoplasmic of the tumor cells forming rosettes. Immunohistochemistry and electron microscopy all suggested that AG has mixed astrocytic and ependymal differentiation. Their cortical localization argues against an origin from native ependymocyte or tanycytes.
It has been suggested that these tumors may derive from the bipolar radial glia that span the neuroepithelium during embryogenesis and that they may share ependymoglial traits of be capable of generating ependymocytes
Surgical excision alone is generally curative. A possible antiepileptogenic effect of radiation therapy is described in one case without surgical resection. The was only one case that recurred (in anaplastic form); this tumor had exhibited typical histologic features at presentation, affected an adult and had been subtotally resected. Further studies are needed in order to expand the information regarding the clinical behavior and therapeutic approach of AG.
Contributed by Xiaomei Ma, MD, Junhui Ge, MD, Liangzhe Wang, MD, Chunyan Xia, MD, Huimin Liu, MD, Yuli Li, MD, Jin He, MD, Weijian Zhu, MD