A female neonate who had an antenatally diagnosed sacralmass is admitted to the neonatal intensive care unit immediately after birth.

The 26-year-old mother had two previous normal pregnancies. In the current pregnancy, a mass was discovered at 20 weeks’ gestation. The woman underwent serial ultrasonographic imaging to monitor the mass. Fetal magnetic resonance imaging obtained at 24 weeks’ gestation revealed a mixed solid-cystic mass in the sacrococcygeal region, extending inferiorly (Figure 2). Elective cesarean section is performed at 37 weeks’ gestation

Abdominal radiographs reveal a 13×15-cm broad-based pedunculated soft-tissue mass projecting from the lower sacrococcygeal area (Figure 3).

Postnatal ultrasonography demonstrates a large mass posterior to the coccyx. The mass has a heterogeneous echotexture with solid, cystic, and vascular components. The lower spinal canal appears normal. Serum α-fetoprotein (AFP) concentration is 335,700 ng/mL (35,700 μg/L). The infant undergoes surgery on the third day after birth. Histopathologic...

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