Anatomic and technical differences when operating in the neck first led physicians to define three different zones, or areas, in which a penetrating missile traverses. Initially, zone 1 was defined as below the clavicle, but injuries proximal (or caudal) to the clavicle are better considered to be thoracic or mediastinal injuries and addressed in that manner. Penetrating injuries superficial to the platysma or in the posterior muscular triangle are considered inconsequential, as no major vascular or aerodigestive structures occupy these regions.

The carotid arterial system carries 90% of the blood flow to the brain. The intracranial collateral circulation varies widely, with a complete circle of Willis present only 20% to 50% of the time. This results in the trauma patient being highly susceptible to ischemic injury when an acute occlusion occurs to either carotid artery. Other collateral systems, such as the external carotid-ophthalmic, occipital-vertebral, and leptomeningeal vessels that may develop over time in chronic occlusive disease, have little benefit in the acute trauma situation. Figure 78-2 demonstrates the anatomy of the lower neck. The common and internal carotid arteries lie within the carotid sheath,
medial to the internal jugular vein, anterior to the vagus nerve, and they usually give off no extracranial branches. The external carotid artery typically has eight major branches, the first being the superior thyroid artery and the terminal branch being the palpable superficial temporal artery. The carotid sinus is a baroreceptor located at the flow divider of the carotid bifurcation. When stimulated, it causes a reduction in the heart rate and blood pressure. The adjacent carotid body is a chemoreceptor responsive to carbon dioxide and will cause an increase in the heart rate and blood pressure when stimulated. Generally, extensive dissection of the carotid bifurcation between the external and internal carotid arteries should be avoided in order to maintain proper function of these structures (Fig. 78-3).

The vertebral arteries arise as the first branch of the subclavian arteries bilaterally (Fig. 78-3). The first segment extends from the subclavian to where it enters the transverse process of the sixth vertebral body. The second segment (longest) lies in the foramina of the transverse processes of the first six vertebrae. The artery is surrounded by a venous plexus that often lends itself to forming AV fistulas following penetrating trauma to this segment. The third segment is short and lies between the atlas (C1) and the foramen magnum at the base of the skull. The fourth segment is intracranial and ends when the two vertebral arteries join together to form the basilar artery of the posterior system. Approximately 15% of patients will demonstrate developmental abnormalities resulting in a unilateral hypoplastic vessel. Another 4% to 5% will lack direct communication of one vertebral with the contralateral side.

Associated injuries are common and should be evaluated separately from potential arterial injuries. The most common associated injury is that to adjacent major veins, occurring in approximately 25% to 30% of cases. Tracheal or laryngeal injuries are found in 9% to 10% of penetrating neck trauma, esophageal or pharyngeal injuries are found in 4% to 5%, and spinal cord or brachial plexus injuries occur in 1% to 2%. Signs and symptoms of these injuries include dysphagia, vomiting, hemoptysis, subcutaneous emphysema, shortness of breath, and enteric contents draining from the wound. Studies have shown a 60% to 80% chance of a positive finding on surgical exploration if crepitance, hoarseness, and stridor are present. Asymptomatic patients with missiles traversing the midline near the aerodigestive tracts should undergo bronchoscopy and an esophagram or high-resolution computed tomography (CT) scan of the neck.

Injuries to the cranial nerves and other important nerves of the neck can occur from both the traumatic event and surgical exploration. It is important to thoroughly evaluate and document each patient for neurologic deficits prior to initiating treatment. The major nerves often injured in the neck, their location, and their resulting deficits are listed in Table 78-1.

Table 78-2 gives a good overall perspective concerning all possible injuries seen in 110 patients with bullet wounds to the neck. Careful auscultation and x-ray of the chest need to be performed in all penetrating neck trauma, as thoracic abnormalities (pneumothorax +/− hemothorax) requiring tube thoracostomy are the most frequently
encountered associated injuries. Generally, a CT scan of the head is also needed (especially in zone 3 injuries) to delineate intrinsic cerebral trauma versus neurologic symptoms secondary to vascular compromise. Any clinical evidence of spinal injury should also warrant a CT scan of the bony neck for definitive evaluation. Associated injuries are a leading cause of death in patients with neck trauma, directly resulting in a mortality rate of 2% to 8%.