Neurogenic thoracic outlet syndrome secondary to an unilateral cervical rib in a poodle mix

A 2-year-old spayed female poodle mix was evaluated for persistent intermittent right thoracic limb lameness and pain refractory to oral analgesic and anti-inflammatory medications. Orthopedic and neurologic physical examinations localized discomfort to the right shoulder and cervical region. Orthogonal right shoulder radiographs did not detect any abnormalities. Magnetic resonance imaging of the right brachial plexus revealed an anomalous bone structure at the level of the right thoracic inlet. Orthogonal cervical radiographs confirmed this finding. Surgical exploration of the right thoracic inlet identified a vestigial rib, extending from the right first rib and compressing adjacent axillary nerves, which was surgically excised via partial costectomy. This unilateral anomaly, analogous to cervical ribs described in human medicine, remains rarely documented in dogs. While rare, neurogenic thoracic outlet syndrome secondary to cervical ribs should be considered in dogs with neck pain and refractory thoracic limb lameness.