Performance of Prenatal Ultrasound Screening for the Relative Positioning of Mesenteric Vessels

Abnormal relative positioning of the superior mesenteric artery (SMA) and vein (SMV) can lead to intestinal malrotation that predisposes to midgut volvulus. The aim of this study was to assess the prenatal ultrasound ability to visualize the relative position of SMA and SMV in normal pregnancies.

Prospective cohort study performed in Montpellier University Hospital Centre, including 80 fetuses during routine 3rd trimester ultrasound scan. For each fetus included, the relative position of the vessels on an axial image was defined as SMV on the right, forward, or on the left of SMA. Doppler imaging was additionally used if necessary. Data were compared to the neonatal abdominal scans performed by pediatric radiologist.

The superior mesenteric vessels were identified in 79 fetuses. Prenatal findings showed a usual relative position of the vessels, that is, the vein on the right of the artery, in 96.2%. In 2 cases, the vein was strictly in front of the artery, and in 1 case, the vein was on the left side of the artery. Seventy-four neonates were examined and comparison with prenatal finding showed a perfect agreement (Kappa coefficient of 100%). An intestinal malrotation was postnatally diagnosed corresponding to the case where vein was on the left side of the artery.

This study showed that the relative position of the SMA and SMV could be assessed using ultrasound prenatal examination with a perfect agreement with postnatal findings. In case of abnormal vessels positioning more examinations should be promote including prenatal MRI and postnatal conventional radiologic examinations to confirm intestinal malrotation.