Supraclavicular Brachial Plexus Block in the Presence of a Cervical Rib

A CERVICAL rib is an extra rib that arises from the seventh cervical vertebra due to a congenital abnormality. Reported incidences range between 0.05 and 3% and can occur unilaterally or bilaterally.¹  We present an ultrasound image of the brachial plexus in the supraclavicular region of a patient who was incidentally found to have bilateral cervical ribs while scanning for a supraclavicular brachial plexus block. Scanning in the supraclavicular fossa revealed an unusually wide separation between the upper/middle and lower trunks of the brachial plexus above the subclavian artery. Proximal scanning revealed a hyperechoic line indicating the presence of a cervical rib. This was seen to lift and divide the lower trunk from the upper and middle trunks (fig.). A posteroanterior chest radiograph confirmed the presence of bilateral cervical ribs.

The supraclavicular block was successfully performed with the needle inserted in a lateral to medial direction, bypassing the cervical rib to block the upper/middle trunks while avoiding the lower trunk in the needling path. The lower trunk was blocked with a separate injection. Seeking the optimal corner pocket would not have resulted in a successful block.²  Awareness of a separate location of the lower trunk is important to ensure an effective block and avoid unintentional neurologic injury. Watanabe et al.³  reported the presence of a cervical rib in a similar patient, but the plexus was identified in one location. Our report emphasizes the importance of thorough scanning of the brachial plexus on both sides of the cervical rib for optimal blockade.