Microtubular aggregates within rough endoplasmic reticulum in myxopapillary ependymoma of the filum terminale.

Aggregates of microtubules with-in rough endoplasmic reticulum were found in many neoplastic cells of three cases of myxopapillary ependymoma of the filum terminale studied ultrastructurally. The cytoplasm and cellular processes of some neoplastic cells were distended by the aggregates. In general the involved rough endoplasmic reticulum contained three to six microtubules, but some enclosed more than 10 microtubules. The enclosed microtubules were straight parallel hollow cylindrical structures with fuzzy coats. They had an inner diameter of 12 to 15 nm, an outer diameter of 30 to 35 nm, and a center-to-center distance of 50 to 62 nm. The involved rough endoplasmic reticulum often showed various degrees of loss of surface ribosomes and some appeared totally degranulated. Vacuolar degeneration of involved rough endoplasmic reticulum with fragmentation and disintegration of the enclosed microtubules was frequent. Direct relationship of the enclosed microtubules to the cytoplasmic microtubules and ciliary formation was not found. This unusual microtubular aggregate has not been described in other types of ependymoma, or in other brain tumors. They may represent a characteristic ultrastructural feature of myxopapillary ependymoma.