Rapid spontaneous malignant progression of supratentorial tanycytic ependymoma with sarcomatous features – “Ependymosarcoma”

Abstract

By analogy to gliosarcoma, the term “ependymosarcoma” has recently been coined to thematize the rare phenomenon of a malignant mesenchymal component arising within an ependymoma. We report on an example of this paradigm, involving tanycytic ependymoma as the host tumor in a 40-year-old female who underwent two tumor extirpation procedures at one-year interval. She first presented with severe headaches, and was seen by imaging to harbor a moderately enhancing mass 2.5 cm in diameter at the rostral septum pellucidum accompanied by occlusive hydrocephalus. Microscopically, the tumor consisted of solid, wavy fascicles of elongated cells that were occasionally interrupted by vague perivascular pseudorosettes. Mitotic activity was absent, and less than 1% of nuclei immunoreacted for MIB-1. A histological diagnosis of tanycytic ependymoma (WHO grade II) was rendered, and no adjuvant therapy given. At recurrence, the lesion was 3.5 cm in diameter, intensely enhancing, and had already seeded into the subarachnoid space. Histology showed a biphasic glial–sarcomatous architecture with remnants of the original ependymoma now displaying hypercellularity and atypical – yet not frankly anaplastic – features. The sarcomatous moiety consisted of spindle and epithelioid cells densely interwoven with reticulin fibers. While the ependymal component was GFAP and S100 protein positive, and featured punctate staining for EMA, none of these markers was expressed in the adjacent sarcoma. Instead, the latter reacted for vimentin and smooth muscle actin. To the best of our knowledge, this is the first documentation of tanycytic ependymoma undergoing malignant transformation, one driven by a highly anaplastic mesenchymal component, corresponding to “ependymosarcoma”.

Introduction

The recognition, since the mid 1990s, that the mesenchymal component of gliosarcoma is clonally derived from neoplastic astrocytes has allowed for a similar phenomenon of sarcomatous evolution in non-astrocytic tumors to be appreciated [2]. Recently, the issue of a mesenchymal malignancy arising within oligodendrogliomas and ependymomas has been systematically addressed by Rodriguez et al. [18], [20]. By analogy to gliosarcoma, it has been proposed that such composite tumors be referred to as “oligosarcoma” and “ependymosarcoma”, respectively.

In contrast to the rather homogeneous nosology of oligodendrogliomas, ependymal tumors comprise several subtypes with significantly different clinicopathologic features and prognosis [3], [15]. Due to the overall rarity of “ependymosarcomas” (Table 1), the propensity of any of these subtypes to engage in sarcomatous transformation has yet to be explored.

In the following, we give an example of malignant progression of supratentorial tanycytic ependymoma with “ependymosarcomatous” features. Tanycytic ependymomas (WHO grade II) comprise the least numerous subgroup of ependymal neoplasia with only 6 intracranial examples on record [4], [8], [10], [16], [17], [25]. Malignant progression of tanycytic ependymoma has not been described previously.