Subungual exostoses--clinicopathological and ultrastructural studies of three cases.

Three patients with subungual exostoses, two involving the great toe and one the fourth toe, are presented. Local excision was performed, and the specimens were processed for light and electron microscopy. Light-microscopic study revealed that the tumours consisted of a proliferative fibrocartilaginous cap that merged into mature trabecular bone at its base. Electron-microscopic examination revealed that the tumour was composed of two types of cells: one was rich in cell organelles including rough endoplasmic reticulum, well-developed Golgi apparatus, and glycogen granules; the other cell had few such cell organelles. The former cells seemed to be osteoblasts actively engaged in bone formation, and the latter to be osteocytes related to those situated deeper in bone matrix in normal bone. However, ossification or calcification in subungual exostosis is rather casual, and osteocytes in this disorder may lack the capacity to elaborate compact bone.