Cervical Rib Synostosis to the First Rib: A Rare Anatomic Variation.

BACKGROUND

Congenital anatomic variations exist in human anatomy, which create both diagnostic and treatment challenges. Understanding the osteologic and radiographic anatomy of supernumerary ribs arising from the cervical spine and recognizing the morphologic variations thereof is of great importance to clinicians, radiologists, and surgeons alike.

CASE DESCRIPTION

This case study describes osteologic morphology and radiologic characteristics of a rare anatomic variant of a cervical rib (CR): a unilateral, right-sided CR synostosis to the first thoracic rib of a 50-year-old South African man of African ancestry. The characteristic features included increased angulation, widening of the body, and shortening of the length of the right-sided first thoracic rib. The synostosis of the CR shaft was at the level of the angle of the first thoracic rib. The widest aspect of the first thoracic rib was close to the site of fusion, namely the angle, with the mediolateral length approximately 34.51 mm. This is in contrast to the contralateral first thoracic rib measuring, at its widest, 26.39 mm. The CR was located approximately 3.34 mm superiorly to the first thoracic rib at the cervical articular facet. The CR presented with a well-defined head, which is small and rounded with the inclusion of an articular facet. Thereafter, it presented with a short neck, just over half the length of the inferiorly placed first thoracic rib, and a similar sized articulating facet at the tubercle. The appearance of the trabecular bone pattern on radiographs is in keeping with the contralateral left first rib, although altered in accordance with the gross osteologic appearance described earlier. Furthermore, the radiographs highlight an elliptical lucent-zone within the trabecular bone demonstrating decreased density centrally with a thin rim of sclerotic cortical bone peripherally. This is consistent with classical rib architecture in cross-section representing the CR shaft site of fusion to the first thoracic rib. The CR synostosis to the first thoracic rib represents a novel complex, termed by the authors as a cervicothoracic rib complex.

CONCLUSION

The present report refers to the osteologic and radiographic description and comparison of a unilateral, right-sided CR synostosis to a first thoracic rib. The clinical implications of CRs may consist of neurologic, vascular complications, and functional deficits of the involved limb associated with thoracic outlet syndrome (TOS). A CR synostosis to the first thoracic rib represents an associated increased risk of vascular injury, with poorer operative outcomes associated with TOS. This case study is of particular importance to vascular surgeons and neurosurgeons involved with surgical planning and intervention strategies relating to CRs and TOS.