Ciliary claws: their existence in various epithelial cysts of the central nervous system.

We describe claw-like projections and their associated structures as encountered at the tips of cilia in a cerebellar epithelial cyst, an intraspinal bronchogenic cyst and two colloid cysts of the third ventricle. Ciliary claws appear either as a single structure or as a cluster of two to five projections measuring 22-28 nm in length and 8-10 nm in diameter, extending from the plasma membrane of the ciliary tip. The transmembranous fibrils of the ciliary claws are bound to a multilayered electron-dense disc which is attached by the distal ends of axonemal microtubules. These observations suggest that ciliary claws are common in several types of epithelial cysts of the central nervous system; the presence of these structures supports the premise that the corresponding epithelium is of endodermal origin.