The epineurium of the nerve is contiguous with the dura mater, providing extra support to the nerve.Brachial plexus lesions typically result from excessive stretching; from rupture injury where the nerve is torn but not at the spinal cord; or from avulsion injuries, where the nerve is torn from its attachment at the spinal cord. A bony fragment, pseudoaneurysm, hematoma, or callus formation of fractured clavicle can also put pressure on the injured nerve, disrupting innervation of the muscles. A trauma directly on the shoulder and neck region can crush the brachial plexus between the clavicle and the first rib.Although injuries can occur at any time, many brachial plexus injuries happen during birth: the babys shoulders may become impacted during the birth process causing the brachial plexus nerves to stretch or tear. Obstetric injuries may occur from mechanical injury involving shoulder dystocia during difficult childbirth, the most common of which result from injurious stretching of the childs brachial plexus during birth, most often during vaginal birth, but occasionally Caesarean section. The excessive stretch results in incomplete sensory and/or motor function of the injured nerve.Injuries to the brachial plexus result from excessive stretching or tearing of the C5-T1 nerve fibers. These injuries can be located in front of or behind the clavicle, nerve disruptions, or root avulsions from the spinal cord. These injuries are diagnosed based on clinical exams, axon reflex testing, and electrophysiological testing. Brachial plexus injuries require quick treatment in order for the patient to make a full functional recovery (Tung, 2003).
In addition, assessment of the cervical cord, post-traumatic changes in soft tissues and associated injuries (e.g. fractures, cuff tears, etc.) may be appreciated. Although superior to nerve conduction studies, ultrasound and other tests, conventional MRI has a poor specificity (72%) meaning that the false-positive rate is high and surgeons cant rely upon the test to guide treatment. Consequently, the future of peripheral nerve MR imaging (including imaging brachial plexus injuries) is likely to be based on diffusion-weighted imaging, such as diffusion tensor techniques, which are of significant potential clinical utility and can enable the production of easily interpreted 3D reconstructions of the spinal cord and brachial plexus such as this. Several weeks/months after BPI, EMG examination can provide additional information about whether the muscle is denervated. These examinations are painful, highly user-dependent and lack normal values so cannot be relied upon. Classification
The severity of brachial plexus injury is determined by the type of nerve damage. There are several different classification systems for grading the severity of nerve and brachial plexus injuries. Most systems attempt to correlate the degree of injury with symptoms, pathology and prognosis. Seddons classification, devised in 1943, continues to be used, and is based on three main types of nerve fiber injury, and whether there is continuity of the nerve. Neurapraxia: The mildest form of nerve injury. It involves an interruption of the nerve conduction without loss of continuity of the axon. Recovery takes place without wallerian degeneration.