The occurrence and characteristics of non-myelinated neuromas within central nervous tissue.

Three cases are described in which neuromas composed of non-myelinated axons were present within central nervous tissues in areas of tissue destruction, together with neuromas of peripheral myelinated axons. The non-myelinated neuromas were larger than the myelinated, but contained very much fewer Schwann cells and less connective tissue fibers. It is suggested that they took origin from heterotopic non-myelinated peripheral nerves, just as the myelinated neuromas are thought to take origin from heterotopic myelinated peripheral nerves. The non-myelinated neuromas are very much less common than the myelinated neuromas, and the inference may be drawn that their nerves of origin may be very much less common, a malformational rarity. Because of their rarity, and the very limited proliferation of Schwann cells which follow their injury, these non-myelinated perivascular nerves are not likely to provide the Schwann cells which produce the regenerated peripheral myelin about some denuded but perserved central axons in myltiple sclerosis. These may take origin from multipotential primitive reticular cells within the central nervous tissues, as is consistent with the thesis perviously offered that Schwann cells are mesenchymal in character. It may also be inferred that any neurogenic control of cerebral circulation would be limited to an effect on the larger, extracerebral vessels in the subarachnoid space.