Anomalies of thoracic outlet in human fetuses: anatomical study

Thoracic outlet syndrome (TOS) identifies the clinical condition determined by the mechanical compression and entrapment of the subclavian vessels and the brachial plexus cords within the space delineated by the scalene muscles, the clavicle, and the first rib. To date, there are no concluding explanations concerning the real causes of the appearance of TOS in children. This is the first study to investigate the existence, frequency, and type of thoracic outlet anomalies in the prenatal stage (human fetuses).

Eighty cervical dissections (40 consecutive spontaneously aborted human fetuses) were performed, and the musculoskeletal, vascular, and nervous elements that pass through the thoraco-cervico-axillary region were investigated.

Overall, anatomical anomalies of the thoraco-cervico-axillary region were found in 60% of the 80 cervical dissections. Nine (22.5%) of the 40 fetuses had normal bilateral anatomy. In 6.3%, the scalene hiatus had an oval shape due to the common costal insertion of the anterior and middle scalene muscles. Fibromuscular bands were found in 15% of the fetuses. Hypertrophy of the anterior scalene muscle was seen in 12.5% of the dissections. In 28.7% of the cervical dissections, hypertrophy of the C7 transversal process was noted, bilateral in seven cases. There was one case of a "C-shaped" clavicle anomaly. The absence of the internal mammary artery was noted in one case.

This study shows that the presence of TOS anomalies in fetuses is not a rare occurrence, emphasizing a pathological cervical background which can be harmful in situations of cervical trauma or inflammatory processes. Having knowledge of the types of anomalies which can lead to TOS is important for performing a complete surgical correction and avoiding the high failure rate of recurrent TOS.