A case study on the pitfalls in prenatal ultrasonic detection of butterfly vertebra

Butterfly vertebra is a rare congenital anomaly that is observed both in isolation and also as part of syndromic diseases. In prenatal ultrasonic scans the typical shapes of the two halves for butterfly vertebra are wedge-shaped or triangular. In the case we presented, the 3 dimensional computed tomography (3D CT) showed that the shape was unusual and rare. To improve the prenatal ultrasonic discriminability of this rare form of butterfly vertebra we used multi-directional ultrasonic images, corresponding to postpartum 3D CT images.

A 25-year-old woman was referred to our department for ultrasound screening. The routine fetal back spinal scan yielded findings indicative of an anomaly within the ninth thoracic vertebral body. The affected vertebra was examined by two-dimensional (2D) and three-dimensional (3D) ultrasound while the fetus was prone and supine. The focussed scanning of the fetal spine from the back, anterior and lateral approaches aided us to reach the final prenatal diagnosis of butterfly vertebra with asymmetric halves.The diagnosis of butterfly vertebra was confirmed by the radiologist with 3D CT after the woman chose to terminate the pregnancy due to multiple malformations. In 3D CT, the body of the ninth thoracic vertebra appeared to be two lateral halves of different sizes, and the bigger half was C-shaped. When prenatal ultrasonic images and postnatal CT images were compared, the echoic shape of the affected vertebra scanned from the front right side was very similar to the CT.

Due to the variable sizes and shapes of vertebrae affected in butterfly vertebra, prenatal diagnosis can be difficult using ultrasound. When the presence of fetal vertebral abnormalities is suspected, it is imperative for sonographers to adopt a comprehensive approach that extends beyond the conventional spinal examination performed solely from the dorsal aspect of the fetus. Instead, a thorough assessment should involve scanning the fetus from various angles, including anterior and lateral perspectives, in order to obtain a comprehensive and detailed evaluation of the identified vertebra.