Myxopapillary ependymoma of the filum terminale. A light and electron microscopic study.

The histology of a myxopapillary ependymoma of the filum terminale in a 15-year-old girl was studied by light and electron microscopy. The neoplasm contained both papillary and compact areas of cell growth. The papillary regions consisted of vacuolated cuboidal cells arranged around hyaline/vascular cores that were variably mucin-positive. In the compact regions, the tumor cells were intensely immunoreactive for glial fibrillary acidic protein and occasionally formed perivascular pseudorosettes. Ultrastructural examination revealed interdigitating cell processes, sometimes resting on a basement membrane. Surface specializations included numerous microvilli and occasional cilia. The cilia had an abnormal microtubular pattern (e.g., 8 + 1, 7 + 0). The cytoplasm of the tumor cells contained numerous 7-10 nm intermediate filaments and large numbers of abnormal microtubular aggregates, consisting of 4 to 50 single microtubules enclosed by a limiting membrane. These microtubular aggregates may represent a characteristic feature of myxopapillary ependymoma of the filum terminale.