Congenital gingival granular cell tumor with smooth muscle cytodifferentiation.

Congenital epulis of the newborn is a rare benign congenital gingival granular cell tumor (GGCT) of unknown histogenesis which occurs most commonly on the gingiva of the anterior maxillary alveolar ridge in girls. The granular cells in this entity are histologically indistinguishable from those in extragingival granular cell tumors, known historically as granular cell myoblastoma (GCM), which occur at any age and appear to be of Schwann cell origin. Ultrastructural, histochemical, and immunohistochemical features of three GGCT were examined and compared to three GCM and a granular cell ameloblastoma. This is the first instance in which the ultrastructure of granular cells in a congenital epulis showed evidence of smooth muscle differentiation. Carcinoembryonic antigen-like immunoreactivity was localized in granular cells from all granular cell tumors studied, but S-100 protein was present only in GCM. The smooth muscle ultrastructural features and the lack of S-100 protein in GGCT strongly suggest a different histogenesis from that of GCM. The GGCT is likely derived from a primitive gingival perivascular mesenchymal cell with the potential for smooth muscle cytodifferentiation.