Difficulties in prenatal diagnosis of tumour in the fetal sacrococcygeal area.

Prenatal ultrasound at the 20th week of gestation revealed a 3-cm tumour in the sacrococcygeal area. Initially, a sacrococcygeal teratoma was suspected on the basis of fetal ultrasonography, which revealed normal heart anatomy and an increasing tumour mass. The diagnosis was then changed to fetus in fetu or teratoma. Prenatal magnetic resonance imaging at the 34th week of pregnancy confirmed the ultrasound diagnosis. No other anomalies were found. Elective caesarean section was performed at term. The care team included a paediatric surgeon, obstetricians, neonatologists, midwives, and an anesthesiologist. A female newborn was delivered in good condition. The tumour was resected in the operating room and mature teratoma was established by histopathological evaluation. Surprisingly, agenesis of the right forearm was revealed which had not been detected prenatally, despite many examinations (both in our hospital and earlier at a primary care obstetrician office).