Answer: Myxopapillary ependymoma

Histology: Myxopapillary ependymomma is noteworthy for its pseudopapillary architecture, perivascular and intercellular mucin deposition and a tendency for the tumor cells to be elongated. Mucin is the lesion’s most conspicuous diagnostic feature and can occur as large extravascular pools but is typically and characteristically confined to the walls of blood vessels. In the usual lesion the neoplastic cells are either columnar or elongated and show only minor variation in nuclear shape, size and chromatin distribution. Adherence of the cells to the blood vessels produces a somewhat papillary appearance but the tumor only infrequently possesses true papillae. In some cases, mucin is so extensive as to separate the neoplastic cells and produce a mucoid lesion that mimics cordoma or carcinoma. In other instances, the glial cytology predominates so that a fibrillar background is present and mucin is confined to small vascular deposits. Rarely, pigmented “melanocytic” cells may be found in ependymoma but the pigment is not, in fact, melanin but is a lipofuscin, which stains strongly with PAS.

Discussion: The classic myxopapillary ependymoma arises within the filum terminale of the spinal cord. Origin from ependymal rests is presumed. Very rare examples may arise intracranially or within the spinal cord. The presence of mucin, the absence of ependymal rosettes, and the location of the lesion distinguish myxopapillary from classic ependymomas. Subependymoma is a highly differentiated and slowly growing glioma composed of ependymal and astrocyte-like cells arising in the walls of the ventricular system. They are most often encountered as incidental postmortem findings. Subependymoma is characterized by highly fibrillar processes that sweep around clusters of nuclei and have frequently prominent microcystic change. The differential diagnosis between schwannoma, paraganglioma and myxopapillary ependymoma is probably more important. Some myxopapillary ependymomas have a solid vesicular and less mucinous pattern that may prompt consideration of schwannoma. The finding of perivascular mucin and pseudorosettes along with the negative S100 protein immunostains will point to myxopapillary ependymoma. Paraganglioma may show radiation of neoplastic cells from vessels and simulate the findings in ependymoma. Usually, however, paraganglioma cells are more obviously epithelial and may exhibit delicate cytoplasmic granularity. A prominent nesting or ribbon pattern of cells is also a distinguishing feature of the neuroendocrine cells of paraganglioma. Chromogranin reactivity in paraganglioma and its absence in ependymoma is another helpful feature. Note that the sustentacular cells of paraganglioma may be GFAP and S-100 protein positive.