Congenital Melanocytic Nevus Mimicking a Coccygeal Pad in the Sacrococcygeal Region.

Congenital melanocytic nevus (CMN) is a benign melanocytic proliferative lesion that presents at birth or in early infancy. When the lesion extends into the deep dermis or subcutaneous tissue, it can form a mass that is clinically and radiologically indistinguishable from other soft tissue tumors. We report a case of sacrococcygeal CMN mimicking a coccygeal pad. An 18-year-old man presented with a sacrococcygeal mass and tenderness. Magnetic resonance imaging and needle biopsy findings suggested a coccygeal pad. Because of persistent pain and the patient's desire for removal, the mass was excised under general anesthesia with periosteal inclusion, and the resulting 95 × 50 mm defect was reconstructed using a right superior gluteal artery perforator flap. Histopathological examination confirmed CMN without malignant features. The flap survived completely, and the postoperative course was uneventful. Tenderness resolved completely, and no local or symptomatic recurrence was observed at 6 months. CMN should be considered in the differential diagnosis of sacrococcygeal masses, and needle biopsy may be insufficient for diagnosing deeply infiltrating lesions.