Meconium pseudocyst presenting as a buttock mass.

A newborn 2.4-kg baby girl with a prenatal diagnosis of sacrococcygeal teratoma by ultrasound had a soft cystic mass extending from the infracoccygeal region into the right buttock. The cyst contained meconium leading to a large retroperitoneal cavity. The cyst was drained through an extended buttock incision, and healed without a site of bowel perforation ever identified. Meconium pseudocyst should be included in the differential diagnosis of sacrococcygeal and buttock tumors in the newborn.