What are symptoms of a cervical rib?

Varies. Many people remain asymptomatic with a cervical rib. The most severe complication is thoracic outlet syndrome caused by compression of the brachial plexus (weakness in affected arm) and/or subclavian artery (decreased pulses in affected arm).
Cervical rib. Cervical ribs are an anomaly that arise from the lowest cervical vertebrae . Perhaps no more than 10% of people who have cervical ribs develop thoracic outlet syndrome and the syndrome may well occur in the absence of ribs. Thoracic outlet syndrome can present as wasting , weakness, numbness, tingling ,swelling and pain of hand or arm . http://patient.info/doctor/cervical-ribs-and-thoracic-outlet.