A 25-year-old woman was referred for evaluation of a 25-week gestation fetus with a huge sacrococcygeal teratoma (SCT). The SCT was initially detected during a routine 20-week ultrasound, and the sacrococcygeal tumor grew dramatically thereafter to become nearly the size of the fetus.

By 25 weeks, polyhydramnios and placentomegaly were noted. Fetal echocardiography revealed that a large portion of the fetal cardiac output perfused the SCT. The placental thickness increased from 40 to 60 mm (normal is 25 mm) in one week, and evidence of fetal hydrops (heart failure) was observed. Maternal tachycardia and proteinuria suggested impending maternal mirror syndrome, where the maternal condition begins to “mirror” that of the sick fetus.

Most fetal SCTs have low malignant potential and a good prognosis after resection. However, prenatally diagnosed SCT or sacrococcygeal tumor associated with hydrops can be rapidly fatal in utero or may lead to polyhydramnios and premature delivery. The high-output cardiac failure is related to a “vascular steal" from the extremely high blood flow through the tumor.

This is the first successful open fetal surgical resection of a sacrococcygeal teratoma with resolution of placentomegaly and hydrops and subsequent birth of a viable newborn. This case demonstrates that resection of a fetal sacrococcygeal teratoma early in the disease can have a successful outcome.