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 2.5cm 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 3.5cm 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".