Antenatal ultrasound finding of a cystic back mass in a fetus with terminal myelocystocele

An ultrasound of a twenty-three weeks fetus showed a cystic mass having a "cyst within a cyst" arising from the distal spine. The posterior fossa was normal with no hydrocephalus. Postnatal MRI confirmed the presence of terminal myelocystocele [TMC]. TMC should be considered in a fetus with a cystic mass over the lower spine especially when a "cyst within a cyst" appearance is present. We present the antenatal ultrasound and postnatal MRI appearance of TMC. As the definitive diagnosis of TMC may be difficult to make on antenatal ultrasound other cystic masses, such as, meningocele, myelomeningocele and cystic sacrococcygeal teratoma should be considered