Angiocentric Glioma, Pilomyxoid Astrocytoma, and Pituicytoma: New Entities in the World Health Organization Classification

Abstract

The 2007 World Health Organization (WHO) Classification of CNS Tumors added three new entities to its compendium of primary CNS neoplasms which are similar in that they consist of relatively monomorphous spindle cells: angiocentric glioma (AG), pilomyxoid astrocytoma (PMA), and pituicytoma. This chapter describes the clinical features, histopathology, diagnosis, treatment, and prognosis of these three newly codified entities. Angiocentric glioma, a cortically-based neoplasm that causes intractable epilepsy in young people, shares many similarities with ependymoma. However, these similarities were not enough to classify it as an ependymoma subtype, and AG is under “Other Neuroepithelial Tumors” in the new classification. A WHO Grade I tumor, it is an indolent, slow-growing neoplasm characterized by bipolar cells with spindled nuclei that tend to cluster around intratumoral vessels (giving this tumor its name). The primary differential diagnosis is cortical ependymoma but also includes pilomyxoid astrocytoma. Angiocentric glioma is usually cured with surgical excision, even in subtotally resected tumors. Pilomyxoid astrocytoma is categorized as an aggressive variant of pilocytic astrocytoma encountered mainly in very young children but may present in older children or adults. PMA is usually located in the optic chiasm/hypothalamic region. Histologically, PMA is a strikingly monomorphous tumor composed of bipolar cells in a richly myxoid background which lacks the biphasic pattern of pilocytic astrocytoma and in which the tumor cells form ependymoma-like perivascular pseudorosettes. Considerations in the differential of PMA include pilocytic astrocytoma with a myxoid component, angiocentric glioma, and infiltrating glioma. Because PMA behaves more aggressively, following a biopsy diagnosis, it is treated with chemotherapy for low-grade gliomas with or without gross total resection, depending on tumor burden. Last, pituicytoma is listed as a separate entity under “Tumors of the Sellar Region” and is a solid tumor of the posterior pituitary and stalk. Thought to be derived from pituicytes, the glial cells of the pituitary stalk and neurohypophysis, this tumor presents in adults as an intrasellar or suprasellar mass causing visual or hormonal disturbances. Histopathologically, pituicytomas are composed of spindled, bipolar cells which arrange themselves in a characteristic storiform pattern. The differential diagnosis of pituicytoma includes pituitary adenoma, spindle cell oncocytoma, and granular cell tumor. Pituicytoma is cured by surgical excision and is WHO Grade I.