Gingival leiomyomatous hamartoma: immunohistochemical and ultrastructural observations.

A rare case of leiomyomatous hamartoma of the gingiva is reported and the immunohistochemical and ultrastructural features described. A polypoid mass which presented with the appearance of a congenital epulis was located in the midline of the maxillary alveolar ridge of a two-year-old boy. Histologically, the mass was without a capsule and was composed mainly of irregularly arranged fasciculi of large spindle cells resembling smooth muscle cells. The immunohistochemical staining for desmin was strongly positive in these cells. Many nerve fibers were intermingled with them. Ultrastructurally, the cytoplasm was filled with thin filaments associated with dense patches. Numerous pinocytotic vesicles were present on the cytoplasmic membrane. These findings indicated that the mass consisted mainly of mature smooth muscle cells. The clinical and histological features suggest that the smooth muscle cells in the lesion are of hamartomatous or choristomatous origin, in contrast to true leiomyoma or granular cell congenital epulis.