Melanocytic nevus of the gingiva associated with mirror-image bi-nucleated cells, nuclear inclusion bodies, and apoptotic bodies: a case report and review of the literature

A case of melanocytic nevus of the gingival mucosa is reported. In a 16-year-old female, tiny black papules were clustered in an area of approximately 2 mm in diameter on the maxillary gingiva. Each papule was clearly demarcated from the surrounding healthy gingival mucosa. A resection biopsy revealed a melanocytic nevus. Each nevus cell nest was clearly separated from neighbouring nests and appeared benign on low power view. However, at high power, pigmented cells associated with mirror-image two-nuclei, nuclear inclusion bodies, and apoptosis were occasionally observed. Pigmented cells were diffusely stained with S100 protein but not HMB45. The Ki-67 (MIB-1) labelling index was very low. The lesion was diagnosed as a benign melanocytic nevus of the gingiva. In contrast to cutaneous melanocytic nevi, pigmented lesions of the gingiva, including the oral cavity, are rare. The pathological findings are described in detail and discussed with a review of the literature.