A Problematic Oral Pigmentation: Deep Penetrating Nevus

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.

The deep penetrating nevus

The deep penetrating nevus (DPN), also known as the plexiform spindle cell nevus, is a pigmented lesion that commonly arises on the head and neck in the first few decades of life. Histopathologically, the DPN is wedge-shaped and contains melanocytes that exhibit deep infiltration into the dermis. Given these features, DPN may clinically and histopathologically mimic malignant melanoma, sparking confusion about the appropriate evaluation and management of these lesions. The goal of this review is to summarize the clinical and histopathological features of DPN and to discuss diagnostic and treatment strategies for dermatologists.