Cervical Ribs
Congenital abnormalities in this region include abnormal formation of cervical ribs.  The cervical rib is an extension of the costal elements of C7.  Although it can be bony, it is often fibrous, extending from C7 to the 1st rib.  The subclavian artery and the lower trunk of the brachial plexus have to deviate superiorly and pass over this abnormal rib.  This may cause symptoms attributable to their compression, known as 'Thoracic Outlet Syndrome'.