Origin of granules in granular cell tumor. Intracellular myelin formation with autodigestion.

Eight cases of granular cell tumor were stained with Luxol fast blue to look for the presence of myelin. Luxol fast blue-positive granules were present in all cases. One case was studied ultrastructurally. It showed evidence of origin of granules as infoldings of cell membrane by a process similar to myelin formation around axons. These infoldings subsequently appear to be phagocytosed by lysosomes, resulting in the typical granules of the granular cell tumor.