Multiple Oral Deep Penetrating Nevi Extending to the Masseter and Buccal Fat Pad.

The deep penetrating nevus (DPN) is a rare benign melanocytic tumor often clinically and histopathologically mistaken for malignant melanoma (MM) and other nevus types. This report describes an extremely rare case of multiple lesions of a large DPN in the oral cavity with extensive infiltration to the minor salivary gland, buccal fat pad, buccinators, and masseter muscles, yet with preservation of the normal anatomic architecture. After receiving a diagnosis of MM in another hospital, the patient was at risk for receiving a wide excision that included the masticatory muscles, facial nerve, and overlying skin. Histopathologically, distinct cellular properties were completely masked with heavy pigmentation, thus precluding a proper distinction of benignity versus malignancy. The proliferative capacity of the tumor was analyzed further by immunohistochemistry of bleached tissue sections and tumor behavior was indirectly evaluated by insufficient tumor stromal interaction, with the conclusion that the specimen was benign. Conservative surgery was limited to the oral cavity. Multiple DPNs in the oral cavity merit attention because of the high risk of being mistaken for MM, which would require a wider surgical excision of the head and neck region.