Abstract
Vertebral artery injury (VAI) during posterior cervical spine surgery is a rare but potentially disastrous complication. Placement of screws in the posterior cervical spine is the most common cause of VAI; however, aberrant anatomy may be a potential cause of inadvertent injury in an otherwise routine exposure of the posterior cervical spine. In this article, Molinari et al described two cases of VAI during the routine exposure of the posterior cervical spine. They discuss the management strategy involved in both cases as well as the anatomical variations of the vertebral artery that may predispose patients to higher risk of injury during the exposure.
In the first case, injury to the vertebral artery was repaired with direct suturing by a vascular surgeon. In the second case, direct repair was not possible and suture ligation was employed. Both patients did well from a neurologic standpoint, without suffering a stroke. As in these cases, the blood loss from VAI can be rapid and create a very stressful situation. The two different approaches to deal with the injury noted in the article serve as a good basis for discussion. Whenever possible, direct repair of the vessel is preferable, ideally by a cerebrovascular neurosurgeon or vascular surgeon. It is desirable to establish patency of distal flow postoperatively with micro-Doppler or indocyanine green intraoperative video angiography. 1 In cases in which direct repair is impossible, tamponade with use of topical hemostatic agents offers a treatment alternative. Caution should be exercised to avoid injection of thrombin-containing agents directly into the tear in the vessel to avoid embolization to the basilar artery.
In the unfortunate event of VAI, it has been our practice to complete the spine surgery (which may need to be modified from the preoperative plan) and to take the patient directly to the neurointerventional suite while still under general anesthesia. Another reasonable alternative approach (as utilized here) is to perform a computed tomography (CT) angiogram to assess the vertebral artery. Benefits of a formal digital subtraction angiogram include a higher-resolution assessment of the injury site and identification of potential dissection, pseudoaneurysm formation (more common with tamponade type external compression rather than direct repair), active bleeding, intraluminal thrombus, and flow limitation. Interventional angiography can be undertaken in an emergent fashion if required, such as in the case of active extravasation. Digital subtraction angiography also has the benefit of a full assessment of collateral circulation. Both posterior communicating arteries can be visualized if present as well as vertebral artery dominance. Knowledge of vertebral artery dominance or redundancy plays an important role if it is necessary to sacrifice an injured vessel that may have been partially repaired but developed an enlarging pseudoaneurysm or in cases of embolic stroke from dissection without complete occlusion or flow limiting dissection from packing the surgical field. The origins of the bilateral posterior inferior cerebellar arteries must also be assessed. The posterior inferior cerebellar arteries irrigate the medulla, and the origin may be extradural in up to 20.8% of patients. 2 A patient without posterior communicating arteries with an enlarging pseudoaneurysm of a highly dominant vertebral artery may require a flow-preserving procedure with stenting and coiling or a flow-diverting stent rather than vertebral artery takedown. 3 Bypass procedures may even need to be considered in rare cases were loss of the injured dominant vertebral artery would compromise the posterior circulation dramatically as in the case of patients without posterior communicating arteries. In cases of dissection, we have found monitoring with transcranial Doppler (TCD) to be helpful to detect microemboli, which may herald the development of a larger intraluminal thrombus if left untreated. Although many patients will be on aspirin after such an injury, in the case of strongly positive microemboli on TCD, patients can be given heparin (if possible due to recent surgery), be treated with dextran, or if necessary undergo vertebral artery takedown to prevent large-scale embolization and stroke. 4 For patients with a small dissection or pseudoaneurysm treated with tamponade, it is important to follow the patients to ensure the pseudoaneurysm does not grow 3 ; this follow-up can be effectively performed with serial CT angiography or formal angiography.
The authors quite elegantly described the paucity of data regarding recommendations for preoperative vascular imaging when performing posterior cervical spine surgery, with or without instrumentation. The authors described data from the Cervical Spine Research Society, which demonstrated a 0.07% overall incidence of VAI. One fifth (22/111) of all injuries involved an anomalous course of the vertebral artery. Death or permanent neurologic sequelae occurred in 9% of cases. Craniovertebral junction vertebral artery anomalies occur in up to 5% of patients according to Uchino et al. 5 As pointed out here, even without dedicated vascular imaging, valuable information can be obtained from routine preoperative CT or magnetic resonance imaging studies. The location and size of the vertebral foramen can give clues to dominance as well as identify an aberrant course and prompt the surgeon to order additional vascular imaging preoperatively such as CT angiography with three-dimensional bony/angiographic reconstructions. It should also be noted that in very elderly patients, the vessels can become very tortuous with age, which may put them at further risk of inadvertent injury during exposure.
As the authors pointed out, VAI is rare in noninstrumented posterior cervical spine procedures. Currently, there are no guidelines on which patients should be getting CT angiography or magnetic resonance angiography for routine posterior cervical exposures. Further discussion is warranted in this area. It is important for all surgeons operating in this area to be familiar with common anatomical variants and to be able to recognize VAI immediately. Once identified, rapid resolution with direct repair if possible is ideal. For cases where bleeding is uncontrollable, then tamponade may be the only option. In such cases, serial vascular imaging postoperatively is required.