Intercellular septate-like junction of neoplastic cells in myxopapillary ependymoma of the filum terminale.

Septate junction, a common intercellular feature of invertebrate epithelium, is absent in most vertebrate tissues. In an ultrastructural study of three cases of myxopapillary ependymoma of the filum terminale, structures similar to septate junction were observed in two cases. They were circumferential bands around the finger-like processes of neoplastic cells in which slightly widened 30-40-nm intercellular spaces (as compared to 15-20 nm in non-junctional region) were transversed at regular intervals by parallel septa resulting in characteristic ladder-like appearance. The electron-dense septa, 30-40 nm in cross-length and 20-30 nm in width, were arranged in a periodicity of 40-50 nm. The septa connected to the outer leaflets of the apposing cytoplasmic membranes which appear undisrupted. Most junctions were short; the longest one contained 15 septa in a length of 1.4 microns. Hemiseptate-like junctions with septa of the same measurements were noted between the processes and the investing basement membrane. Junctional complexes such as zonula adherens and gap junction were present in the vicinity. They may represent a specific intercellular feature of myxopapillary ependymoma, and function as cellular adhesions and a mechanical support of the neoplastic cells.