Histological features of congenital lipomas of the lower spinal canal.

A study of 20 children with lipomyelomeningocele and two with intradural lipoma who underwent surgery revealed that five children had unusual and previously unreported histological findings. In each, the characteristic densely fibrous lipoma was present. One patient with an intradural lipoma had an ependymal-lined canal resembling a terminal ventricle. The subependymal layer was neuroglial and striated muscle fibers were scattered throughout adjacent connective tissue and lipoma. Three other children presented with lipomyelomeningoceles. In each case, the lipoma tapered to a firm fibrous tract which blended into conus medullaris. Microscopic examination of this fibrous tract showed it to contain not only a relatively acellular connective tissue stroma, but, in one case, sheets or islands of neuroglia and scattered nerve cells, in another, an epithelial cyst with a smooth muscle and fibrous tissue wall, and in a third case, a fragment of embryonic bone. These findings support the theory that there is a secondary phase to caudal neural tube development, and that congenital lipomas are formed by persistence and differentiation of ordinarily vestigial pluripotential embryonic cells. The fifth case, with extradural lipoma, diastematomyelia, and congenital dermal sinus, had a cyst at the junction of these structures. The cyst was lined by ciliated respiratory-like epithelium, and had mucous and serous glands in its wall. This finding supports the concept that formation of diastematomyelia depends on the prior existence of an accessory neurenteric canal.