Antenatal 3D Ultrasound Detection of Unilateral Rib Agenesis: A Rare Congenital Anomaly

Congenital absence of ribs is quite an unusual entity that can present as an isolated finding or as a part of a syndrome. Rib defects may be associated with maldevelopment of the vertebral column or thoracic musculature. The congenital rib agenesis has been reported postnatally in a few case reports. We present a case of a primigravida referred for an anomaly scan at 20 weeks gestational age. On ultrasonography (USG), the fetus showed unilateral absence of left 5th–8th ribs with associated dysmorphism of other ipsilateral ribs, a right-sided lumbar supernumerary rib, and vertebral segmentation anomalies. The bony defects were well demonstrated by three-dimensional (3D) transabdominal USG. In our case, the unilateral rib agenesis was detected antenatally with no such report published earlier in the scientific literature.