Tailgut cyst (Retrorectal hamartoma): report of a pediatric case.

Tailgut cyst (TGC) is an uncommon congenital lesion, located in the retrorectal/presacral space. We report a 12-year-old girl with lumbar pain and a retrorectal mass. She had mental retardation, hypothyroidism, didelphus uterus, sacrum vertebrae, and coccyx agenesis, without chromosomic anomalies. Three surgeries were performed for the complete excision of the tumor. Microscopically, the mass consisted of cystic spaces lined by a wide variety of epithelia and a stroma composed of fibrous tissue containing bundles of smooth muscle fibers. According to these findings, the diagnosis was TGC. This is a rare congenital lesion that usually presents as a multiloculated cyst in the retrorectal space of young women; TGC requires complete surgical excision to prevent recurrences, infections, and malignant transformation. This case was unique because of the association of TGC with other malformative features and concomitant disease in a pediatric patient.