The diagnosis of the specific neurologic lesion that produces pain in the neck and arm may present a difficult problem. Obviously these pain impulses that arise centrally or peripherally mediate through the cervical or brachial plexuses. Since the type of cases we have under consideration involves the brachial plexus, and since the lesion is peripheral to the spinal cord, careful attention to this portion of the nervous system should be our first endeavor.
The brachial plexus is a somewhat intricate interlacement of the primary divisions of the lower four cervical nerves, the first thoracic nerve, and occasionally an added branch from the fourth cervical and second thoracic segments. These nerve radicles pass through the foramina of the spine and form fasciculi, which in turn pass downward between the scalenus anticus and medius muscles, then under the clavicle and into the apex of the axilla for distribution to the arm.
In peripheral lesions of this group of nerves we must differentiate first between the effects of pressure on the nerve radicles producing sensory changes such as pain and paresthesia of a segmental type and second, injury to the main nerve trunks. The principal causes of the former are lesions such as tumors, protruded disks, or osteophytes which involve or compress the nerve radicles in the spinal canal or within the spinal foramina. In the latter or peripheral brachial plexus lesions there are pathologic conditions producing pressure or irritation in the neck, axilla, or arm. Therefore, if one plots out the sensory. . .