h1 class=”calibre8″>13 Cervical Spine Trauma-Induced Vertebral Artery Injury

Rahul Goel, Hanna Sandhu, I. David Kaye, Hamadi Murphy, Mayan Lendner, and Alexander R. Vaccaro

Keywords: spine surgery, cervical spine trauma, vertebral artery injury, vertebrobasilar insufficiency, CT angiography, anticoagulation

13.1 Introduction

Vertebral artery injury (VAI) in conjunction with cervical spine trauma can occur secondary to blunt or penetrating injuries of the cervical spine. These injuries, such as thrombi, secondary emboli, or dissections, can often initially present asymptomatically, ¹ but their sequelae, such as stroke or even death, can be devastating. ² The low incidence of these frequently asymptomatic injuries has made diagnosis challenging and the potential for devastating outcomes for both symptomatic and initially asymptomatic injuries, especially in cases requiring surgical management of the spine injury, has made management more nuanced.

13.2 Anatomy

The vertebral arteries arise from the posterosuperior aspect of the first segment of the subclavian arteries, distal to the origin of the common carotid arteries. At times there can be aberrant origination of these arteries, more commonly on the left than the right, ³ and most commonly from the arch of the aorta rather than the subclavian artery. From their origination from the subclavian arteries to their joining at the pontomedullary junction to form the basilar artery, the vertebral arteries can be divided into four segments (V1–V4). The first segment (V1) travels from the origin at the subclavian artery to the transverse process of C6. The second portion (V2) travels cranially through the transverse foramina of C6 to C2. At the level of C2, the artery must course laterally to pass through the foramen transversarium of C1. The third segment (V3) then courses posteromedially along the arch of the atlas prior to turning anteromedially to enter the skull through the foramen magnum. The fourth segment (V4) courses medially once entering the skull to combine with the contralateral vertebral artery to form the basilar artery, which supplies the posterior circulation of the brain through the circle of Willis.

13.3 Epidemiology

Identification of VAIs has steadily increased as imaging modalities for these injuries have improved and are more utilized. ⁴ Carpenter was the first to describe this injury in association with cervical spine trauma. ⁵ Subsequently, small cohort studies have reported various rates of VAI with concomitant cervical spine trauma. Weller et al showed a VAI incidence of 33% (4/12) for patients who had a magnetic resonance imaging (MRI) following detection of foramen transversarium fracture on computed tomography (CT) scan. ⁶ Parbhoo et al found an incidence of 25% (12/47) in a prospective study evaluating cervical trauma patients with MRI and magnetic resonance angiography (MRA). ⁷

Larger studies with more extensive screening have found similar results. Miller et al screened all patients with cervical spine fractures, LeFort II or III facial fractures, Horner syndrome, basilar skull fractures involving the foramen lacerum, soft-tissue injuries in the neck, or neurological symptoms otherwise unexplained by intracranial injuries with four vessel cerebral angiography and found a 19% (43/216) incidence of VAI and 11% (24/216) incidence of carotid artery injury (CAI). ⁸ Ren et al prospectively examined 319 patients with closed cervical trauma with two-dimensional time-of-flight MRA and found an incidence of VAI to be 16% (52/319). ⁹ Vaccaro et al had previously identified a similar incidence of VAI (19.7%) in cervical spine injuries screened with MRA, although in a smaller cohort (12/61). ¹⁰ Ren et al and Vaccaro et al found that 50 to 65% of patients with facet joint dislocation sustained VAI, the most common associated cervical spine injury in their series respectively.

Cothren et al evaluated all blunt trauma admissions in their facility and found that three cervical spine pathologies were associated with a much higher incidence of VAI: subluxations, upper cervical spine fractures (C1–C3), and fractures through the transverse foramen. ¹¹ These findings have been corroborated in various literature. ^2,10 Furthermore, large database studies have found that the overall incidence of VAI in all blunt traumas range from 0.075 to 1.14%. ^12,13,14,15

13.4 Mechanism and Types of Arterial Injury

VAI is possible in any of the four segments of vertebral artery; however, the most often injured segment of the vertebral artery is the V2 segment due to its relatively fixed position and the narrow space that it occupies. ^16,17,18,19 Chung et al found that the greatest risk factor for injury of the vertebral artery at this segment, V2, was facet fracture with an odds ratio of 20.98 in their multivariate analysis. The authors postulated that the already narrow transforaminal space predisposes the artery to damage with further fracture fragment encroachment. ²⁰

The most common mechanism associated with VAI has been shown to be a flexion-type force in the cervical spine, most commonly flexion-distraction (▶ Fig. 13.1), but also flexion-compression. ^21,22 Sim et al evaluated flexion-type force and its compression of the vertebral artery in cadaveric models, finding that once the physiological flexion range of motion was exceeded, there was impingement upon the vertebral artery. ²³ As the flexion force exceeds the physiologic range of motion, the vessel attachments to the surrounding tissues begin to apply shearing forces to the intimal lining. Tears that occur subsequent to this force can lead to thrombus formation and occlusion of the vertebral vessel.

The most common VAI pattern seen is occlusion ²⁴ followed by dissection. ¹⁷ The adventitia of the vertebral vessel is relatively resistant to tears as compared to the intima. Due to this, tears within the intima can propagate, creating a dissection plane between these two layers of the vessel. Thrombus formation between these two layers can begin to compress the vessel lumen leading to turbulent flow and occlusion. Occlusion can also occur through direct compression of the vessel from fracture and dislocation fragments.

13.5 Clinical Diagnosis

13.5.1 Presentation

Due to abundant collateral circulation feeding the vertebrobasilar system and posterior circulation of the brain, patients with VAI are often asymptomatic. In the case of atherosclerosis or anatomic variations that cause collateral circulation to be diminished, patients may present with symptoms of vertebrobasilar insufficiency (VBI) such as vertigo, dizziness, dysarthria, blurred vision, tinnitus, dysphagia, and diplopia. ²⁵

The interval between spinal injury and development of symptoms varies greatly ranging from immediately after the trauma to up to 3 months later. ²⁶ Embolism, thrombus extension, or dissection of the vertebral artery can cause acute or delayed onset of symptoms in initially asymptomatic patients. Heros et al described a patient with VAI who developed a delayed cerebellar infarction in the setting of a normal contralateral artery secondary to a thrombus that had extended distally to the intracranial portion of the vertebral artery. ²⁷ In another case study, Six et al reported a 25-year-old asymptomatic patient who presented with bilateral vertebral artery occlusion and minimal subluxation of C2 on C3. ²⁸ Angiography revealed occlusion of both vertebral arteries but the presence of collateral circulation by the vessels of the thyrocervical trunk and superficial occipital artery. In a retrospective review of 1,283 patients with cervical spine trauma, Blam et al determined that a normal neurological examination was not indicative of vertebral artery patency after cervical spine trauma. ²⁹ Furthermore, VAI was observed in similar frequency among neurologically intact patients as compared with motor incomplete patients.

The late onset of symptoms following VAI suggests that thrombus formation at the injury site followed by clot propagation and subsequent infarction may be the culprit. Therefore, it is important for clinicians to recognize that neurological signs or symptoms of VBI may be delayed, and to consistently monitor a patient’s response to treatment both initially and upon subsequent follow-up visits.

13.5.2 Imaging Modalities

Digital subtraction angiography (DSA) is a fluoroscopic technique that allows visualization of blood vessels in contrast with their surrounding bone and soft tissue. DSA has been the “gold standard” for evaluation of residual or recurrent aneurysms after microsurgical clipping. ³⁰ DSA has been proven to be especially useful in detection of vertebral artery abnormalities, including occlusions, ulcerated plaques, aneurysms, and stenoses. DSA systems use X-ray detection to produce 1 to 30 exposures per second of an intra-arterial contrast medium. These arterial images are then converted to digital form and are used to “subtract” the precontrast images from those obtained after injection to visualize arterial structure prior to puncture. DSA examinations can be performed on an outpatient basis and often require 25 to 45 minutes, putting them at a considerable advantage in safety and cost over standard arteriographic examinations, which require overnight observation to detect arterial obstruction or hemorrhage. While there are no randomized clinical studies that document direct or indirect safety effects of DSA, certain complications can arise in DSA exams due to leakage of contrast medium and should be considered in clinical decision-making.

As a less invasive imaging modality, computed tomography angiography (CTA) has begun to replace DSA at many institutions. Unlike DSA, CTA does not require femoral artery puncture or intra-arterial manipulation. In addition, CTA requires fewer personnel, is less time-consuming, requires considerably less contrast, and rarely requires sedation, thereby minimizing anesthesia-related risks. A primary concern with CTA is clip-induced imaging artifacts that may obscure local anatomy and limit analysis of the arterial region of interest.

Imaging modalities used in the radiological examination of high-energy trauma (e.g., fall from a great height, motor vehicle accident, sports-related trauma) often require head and cervical spine CT scans. As a result, many studies have advocated the incorporation of CTA as part of the initial screening of patients presenting with penetrating cervical injury without indication of immediate operation. An 11-month prospective study conducted at the Parkland Memorial Hospital Trauma Center underscored the importance of CTA as a screening tool in addition to CT since it identified 98% of blunt cervical vascular injuries (BCVIs) and provided improved visualization of both normal and abnormal anatomy allowing clinicans to make sound judgments regarding at-risk structures. ³¹ Eastman et al conducted a study on 162 patients at risk for BCVI which revealed that the results of CTA and DSA were concordant for detection of VAI. ³¹

Despite wide acceptance in the radiology literature, many clinicians remain skeptical of CTA. ³² Although CTA is less invasive and provides short examination times, its insufficient sensitivity has made clinicians reluctant to use CTA over DSA as the initial screening modality of choice when identifying VAI. In a 40-month study comprising 7,000 blunt trauma patients, Malhotra et al selected 119 patients for DSA and CTA screening based on criteria including facial and cervical spinal fractures and unexplained neurological deficit. ³³ 6 of 62 (10%) CTAs were false positives, which resulted in a sensitivity of 74% and negative predictive value (NPV) of 90%. Factors leading to CTAs being suboptimal include patient factors, such as dental work or foreign metal objects, and technical factors, such as poor contrast in the arteries and motion artifacts. Similarly, Biffl et al found an alarming rate of failures of CTA to detect subtle lesions that were visualized using DSA. ³⁴

MRA uses MRI and an injection of gadolinium-based contrast material to visualize arterial blood flow. Since the exam does not use ionizing radiation, it is less likely to cause an allergic reaction. Other advantages of MRA include absence of flow-related enhancement of an artery, which may indicate occlusion and presence of pseudoaneurysms (▶ Fig. 13.2). Although a number of studies describe the use of MRA to identify BCVI, there is a paucity of literature regarding the sensitivity and specificity of MRA in patients with VAI.

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