Benign sacrococcygeal neoplasm arising at birth from a giant congenital melanocytic nevus.

Giant congenital melanocytic nevi (CMN) are considered to be premalignant with the highest risk for conversion to melanoma. Solid tumors within giant CMN presenting at birth are relatively unusual, and a variety of malignancies have been reported within these masses. However, the frequency of malignancy in these tumors is unknown. We report the unusual case of a female neonate who was born with 2 large, perianal masses within a giant CMN over her trunk. We resected the larger of the 2 masses because of discomfort and bleeding. The mass consisted of an outgrowth of melanocytes with benign characteristics. The smaller of the 2 masses was managed expectantly and has subsequently decreased in size. We propose that pathologically benign masses within giant CMNs may not require immediate resection. We will discuss the management and pathologic findings of this case and review the literature regarding management of CMN-associated neoplasms arising at birth.