Antero-inferior paralabral cyst of the shoulder: An atypical cause of rapidly evolving axillary and musculocutaneous nerve palsy

Paralabral cysts of the shoulder are a rare cause of shoulder pain. Their association with neurological symptoms is uncommon. This case report presents an antero-inferior paralabral cyst in a painful atraumatic shoulder causing axillary and musculocutaneous nerve palsy. The patient in the present study showed a rapidly worsening active shoulder function with dull pain in the posterior shoulder and hypoesthesia over the deltoid. Magnetic resonance imaging revealed an antero-inferior paralabral cyst. Electromyography showed a profuse denervation of the deltoid, teres minor and biceps brachii muscles. The patient was diagnosed with a axillary and musculocutaneous nerve compression neuropathy caused by the cyst. Shoulder arthroscopy was performed with the goal of decompressing the cyst and explore the terminal branches of the brachial plexus. During surgery a partial labral tear was detected and anatomically repaired after cyst resection. Exploration of the terminal roots of the plexus brachialis showed the presence of dense fibrotic tissue that was released. Shoulder function recovered completely after surgery. Paralabral cysts are rare and surgical management consists of cyst removal and labral repair. In presence of neurological symptoms exploring the retrocoracoid plexus may be a useful option to check for fibrosis around the nerves that could limit or slow down nerve recovery.