Penetrating Injuries of the Neck Workup

Laboratory and radiologic workup for patients with penetrating trauma to the neck requires a tailored approach based on their injury location, severity, and hemodynamic status.

All trauma patients should undergo the following preliminary laboratory tests:

• Hemoglobin and hematocrit level, to determine the degree of blood loss or detect underlying anemia

• Glucose level, which can affect level of consciousness

• Electrolyte levels (basic electrolyte panel), to detect metabolic disturbances

• Consider blood typing and cross-match for patients with blood loss

An arterial blood gas concentration is obtained in every patient with respiratory compromise.

After initial stabilization, laboratory studies are tailored to each patient's injuries and past medical history.

Patients with stable vitals and no hard clinical signs of major vascular or aerodigestive tract injury can be evaluated with a variety of imaging modalities.

CT scanning  ^[15]

Multi-detector CT angiography (MDCTA) can be used to obtain noninvasive, fast, and reliable assessment of vascular and aerodigestive tract injuries. A recent prospective multicenter study found MDCTA to be 100% sensitive and 97.5% specific in hemodynamically stable patients with soft signs following penetrating neck injuries. ^[16] MDCTA can be a valuable tool in identifying patients who can be safely observed and direct therapy in others by facilitating anatomical localization of injury and identifying the trajectory of the object resulting in the injury. Additionally, CT imaging may identify retained foreign bodies. 

MDCTA may be used in lieu of invasive arteriography for vascular assessment, except when beam artifact from a retained foreign body hinders a reliable study or when angiographic embolization of a known vascular injury is anticipated. ^[12]

The sensitivity of MDCTA in detecting arterial injuries following penetrating neck trauma ranges between 75.7% and 82.2%. The technique is highly specific in identifying penetrating injuries to the arteries in the neck (96.4-98.4%). The sensitivity of the test in detecting internal carotid and vertebral artery injuries was far better than that for external carotid artery injuries. ^[17]

A CT scan of the neck is useful for the evaluation of patients with suspected laryngeal injuries and a stable patent airway. Patients with open lacerations of the larynx, lacerations crossing the vocal cords, disruption of the anterior commissure, subluxed arytenoid cartilages, exposed cartilage, or obvious crush injuries of the larynx require surgery and are not likely to benefit from CT evaluation.

A CT scan is generally the best imaging modality in the evaluation of a penetrating injury when a retained foreign body is suspected. It is useful in identifying metallic objects, including missiles, as well as most radiolucent foreign bodies, including those made of plastic and wood. CT scanning is also useful in defining the relationships of foreign bodies to surrounding muscles, bone, and soft tissues. However, CT scanning is limited in the identification of very small foreign bodies and those with a density similar to that of the surrounding soft tissues, such as some wood fragments. When a foreign body is strongly suspected, exploration may be indicated despite a negative finding on CT scan.

Contrast-enhanced esophagography

Esophageal injuries may be diagnosed with contrast-enhanced esophagography; however, the sensitivity of this test is reported to be only 70-80%. The use of water-soluble contrast material such as Gastrografin is preferred to prevent barium-induced mediastinitis or pneumonitis.

In comparison, barium studies are reported to have a higher sensitivity, and some authors recommend repeating esophagography with barium in patients with a negative Gastrografin finding who have a high likelihood of esophageal injury.

Doppler ultrasonography

This study is used to assess stenosis or aneurysm formation after major injuries to the carotid artery are repaired. Duplex ultrasounds may be used in lieu of invasive arteriography for assessment of zone 2 neck injuries. ^[12]

Radiography

Plain radiographs of the neck may be useful in identifying foreign bodies and free air. Air in the prevertebral or deep neck spaces suggests injury to the larynx or trachea. Pneumomediastinum and pneumothorax are suggestive of airway injury.

Guidelines

While clinicians should tailor the use of imaging studies and other ancillary diagnostic tests in the context of the patient's clinical condition; other, coexisting injuries; and care priorities determined as part of trauma evaluation, the American College of Radiology Appropriateness Criteria for penetrating neck injury, published in 2017, may provide a framework for imaging for patients who suffer penetrating neck injuries ^[18] :

• In patients with penetrating neck injuries with clinical soft injury signs and in patients with hard signs of injury who do not require immediate surgical exploration, CT angiography of the neck is the preferred imaging procedure to evaluate the extent of injury
• When a clinical concern remains for vascular injury despite a normal or equivocal CT angiography scan of the neck, catheter-based arteriography is useful for further evaluation; the benefit of arteriography is the ability to perform, in tandem, an endovascular procedure if needed
• If a concern remains for aerodigestive injury despite a normal or equivocal CT angiography scan of the neck, a radiographic single-contrast esophagram may be considered, but it should be used in conjunction with direct visualization techniques

Flexible laryngoscopy

Flexible laryngoscopy is an extremely useful technique for the evaluation of patients with laryngotracheal trauma. It is easily performed at the bedside and provides excellent depiction of the upper airway and larynx.

Both the oropharynx and hypopharynx are examined for hematomas or lacerations. The larynx is inspected for mucosal tears, exposed cartilage, hematoma, and edema. The position and motion of the arytenoid cartilages are noted, as is the degree of vocal cord closure.

Angiography

The merits of routine angiography versus selective angiography continue to be debated. Many authors believe that physical examination is inadequate for the evaluation of arterial injuries in penetrating neck injury and recommend routine angiography for all proximity injuries. In a prospective study that included 176 hemodynamically stable patients with penetrating neck injury, routine angiography depicted vascular injuries in 19%, and only 8% required intervention. Most centers follow a protocol of selective angiography in which both symptomatic and asymptomatic zone 1 and zone 3 injuries are routinely evaluated with angiography. These zones are difficult to assess clinically, and surgical access is challenging. Zone 2 injuries are usually explored surgically if they are symptomatic, and they can be followed up clinically or evaluated with angiography if they are asymptomatic.

However, techniques such as MDCTA have high sensitivity and specificity in predicting and evaluating vascular injuries to the neck. ^[16] As a result, invasive angiography is only obtained when beam artifact from a retained foreign body hinders a reliable study or when angiographic embolization of a known vascular injury is required.

Angioembolization techniques can be used to control bleeding, especially in areas that are difficult to access, such as the base of the skull. Balloon occlusion can be used to control hemorrhage temporarily until vascular access is obtained, or vessels can be embolized if they are considered expendable or surgically inaccessible.