Production of myelin by neoplastic cells.

Formation of myelin sheaths by neoplastic cells was found in a spinal ganglioneuroma. All phases of initial myelination were observed including the formation of a mesaxonal spiral and the fusion of its lamellae into a major dense line. A unique aspect of neoplastic myelin formation was the formation of sheaths around bundles of extracellular fibrils rather than axons or cell processes. Formation of myelin sheaths around extracellular material has never been observed before. The findings have implications on the mechanisms controlling initial myelination.