Prenatal Diagnosis of Extra-Abdominal Intra-Amniotic Umbilical Vein Aneurysm: A Case Report with Ultrasound Imaging Features

Abstract Extra-abdominal intra-amniotic umbilical vein aneurysm (IAUVA) is an exceptionally rare vascular anomaly of the umbilical cord and is associated with significant perinatal risk. Prenatal diagnosis may be challenging because grayscale findings can mimic nonvascular cystic lesions of the umbilical cord. Doppler ultrasound plays a critical role in accurate diagnosis by demonstrating characteristic venous flow patterns within the lesion. We report a prenatal case of extra-abdominal IAUVA diagnosed using grayscale and Doppler ultrasound. Imaging demonstrated a cystic venous dilatation measuring approximately 21.5 × 19.1 mm within the free-floating segment of the umbilical cord with internal turbulent venous flow producing a characteristic yin–yang sign on color Doppler and nonpulsatile turbulent waveform on spectral Doppler. Associated antenatal ultrasound findings included dilated fetal bowel loops, and postnatal evaluation confirmed ileal atresia requiring surgical correction. Recognition of these imaging features is essential to differentiate this condition from avascular cord cysts and to enable appropriate antenatal surveillance and perinatal management. This case underscores the importance of systematic Doppler evaluation of umbilical cord cystic lesions and highlights the need for awareness of potential associated fetal gastrointestinal pathology.