Penetrating neck trauma is a serious cause of morbidity and mortality in the acutely injured patient. While a "no-zone" management approach to penetrating neck injuries is replacing the traditional three zone approach, knowledge of neck zone anatomy is crucial to anticipating and diagnosing pathology inherent to each zone. Zone I is the most caudal and includes the base of the neck and thoracic inlet. It extends from the sternal notch and clavicles to the cricoid cartilage. Zone I contains the following structures:

• ●Thoracic outlet vasculature (subclavian arteries and veins, internal jugular veins)
• Proximal carotid arteries
• Vertebral artery
• Apices of the lungs
• Trachea
• Esophagus
• Spinal cord
• Thoracic duct
• Thyroid gland

While penetrating injury to Zone I of the neck is classically from a missile (bullet, fragment, etc) or the downward motion of a stabbing injury, injury to the vital structures in Zone I of the neck can happen from any mechanism. In stable patients who do not meet criteria for emergent transfer to the operating room, further evaluation is typically proceeded with CT angiography of the neck. Peripheral IV placement is a commonly overlooked aspect to care of these patients that can serve to significantly increase or decrease your diagnostic yield depending on which side the IV is placed. 

During a CTA of the neck, IV contrast is injected into a patient's arm and pools in the large, subclavian vein. At this point, the CT images are taken. The pooled contrast causes signifcant streak artifact and obstructs adequate view of the subclavian artery and the base of the carotid artery. If patient's IV is on the same side as the penetrating neck injury, streak artifact from the pooled contrast will significantly decrease the diagnostic yield of pathology to those arterial structures. Also, if the penetrating injury damaged venous structures, injection of IV contrast on the same side could cause extravasation of contrast and limit visibility in that region on CT. It is therefore preferred that contrast be injected in the arm contralateral to the side of the inujury. Knowledge of this technical limitation of CT and recognition of which arm contrast is being injected will greatly decrease or increase your diagnostic yield in patients with penetrating injury to Zone I of the neck.

Below is a CT image highlighting this phenomenon. Contrast was injected into the right arm of the patient and is pooling in the right subclavian vein. The view of the left great vessels is far superior to the view of the right, which is significantly limited by streak artifact from the contrast.:  

References:

• Newton, MD, Kim. "Penetrating neck injuries: Initial evaluation and management." UpToDate. June 2016. https://www.uptodate.com/contents/penetrating-neck-injuries-initial-evaluation-and-management?source=search_result&search=penetrating+neck+trauma&selectedTitle=1%7E23