A Peculiar Accessory Scrotum With a Human Tail-Like Structure: A Case Report.

Accessory scrotum is a rare congenital anomaly resulting from aberrant scrotal development. It is usually present at birth in the perineum of male infants and is often associated with a lipoma at its base. Here, we report a peculiar case of an accessory scrotum present at birth on the skin adjacent to the anus. The accessory scrotum was continuous with a narrow stalk consisting of longitudinally oriented connective tissue and nerve bundles within the fatty tissue, which further extended to a terminal nodule containing articular cartilage and marrow tissues in the ischiorectal fossa, forming a 7-cm-long structure. The components of the stalk and terminal nodule resembled those described in the human tail but ran subcutaneously without a skin covering. Therefore, the lesion was diagnosed as an accessory scrotum with a human tail-like structure. The lesion was completely resected at 10 months of age. Preoperative whole-body computed tomography revealed no other anomalies, and the infant demonstrated normal development approximately 1 year postoperatively. To our knowledge, no similar cases have been reported, and its histogenesis remains unexplained. We postulated that this lesion may result from the ectopic migration of pluripotent cells derived from the tail bud during early embryonic development. This case provides unique insights into the shared embryological mechanisms between accessory scrotum and human tail-like anomalies.