Infratentorial giant cell ependymoma: a rare variant of ependymoma

Abstract

We describe a giant cell ependymoma occurring in a 50-year-old man. The mass was located in the posterior aspect of the foramen magnum, extending from the cerebellar tonsil to the upper cervical spine. The tumor was a highly cellular neoplasm showing biphasic histology. Diffuse sheets of non-cohesive atypical giant cells, having eccentrically located single or multiple nuclei and plump eosinophilic cytoplasm, partly infiltrated the desmoplastic inflammatory stroma. Parts of perivascular pseudorosette-forming or pseudopapillary areas were composed of atypically elongated cells, which looked like conventional anaplastic ependymoma. There was a transitional area between two patterns. Numerous mitoses and focal necrosis were observed. Immunohistochemically, the tumor cells were immunoreactive for glial fibrillary acidic protein, vimentin, S-100 protein, and CD99. None of the tumor cells showed immunoreactivity for epithelial membrane antigen except for the intracytoplasmic lumen of a few vacuolated cells. Ultrastructurally, tumor cells were ependymal in nature; we noted cytoplasmic intermediate filaments and intercellular microrosettes with microvilli, cilia, and long zonula adherens. The features of this tumor, e.g. its superficial location, mixed giant cells, perivascular pseudorosettes or papillaries, complicated its differentiation from rhabdoid/papillary meningioma. However, immunohistochemistry and electron microscopy confirmed the diagnosis of ependymoma. The giant cell variant should be included in the subclassification of the ependymoma.

Introduction

Ependymoma is a slow-growing neuroepithelial neoplasm predominantly affecting children and young adults. It occurs along the neuroaxis in association with the ventricular system; however, extraventricular ependymoma thought to originate from embryonic ependymal remnants has also been reported [16]. Infratentorial ependymoma predominates in children, and spinal ependymoma is common in adults. Ependymoma shows a variable biologic behavior; to date, a consistent histologic parameter predicting the patient's outcome has not been established. Besides the typical histopathology, official variants such as cellular, papillary, clear cell, and tanycytic ependymoma are well known [9]. Other rare tumors having lipidized cells, giant cells, and signet ring cells have also been mentioned in the literature [1], [6], [7], [12], [13], [14], [18], [20], [22], [27], [28]. Here, we report on the second adult-affecting and the first cerebellar case showing features of anaplastic giant cell ependymoma. As this rare variant of ependymoma has been described in the literature only sporadically [1], [6], [11], [13], [27], this case could help to understand the pathologic and clinical features of giant cell ependymoma.