Safety of Unilateral Endovascular Occlusion of the Cervical Segment of the Vertebral Artery without Antecedent Balloon Test Occlusion

Safety of Unilateral Vertebral Artery Occlusion

Surgical ligation and endovascular deconstruction or segmental occlusion of the vertebral artery has long been used to facilitate resection of cervical spinal tumors and treat difficult intracranial aneurysms.^1,4⇓–6 In some cases, surgical or endovascular vessel sacrifice can obviate complex skull base surgery. Dissecting aneurysms of the intracranial vertebral artery are particularly difficult to reconstruct surgically and have been treated successfully with proximal vertebral artery or endovascular segmental occlusion of the affected vessel.^7⇓⇓–10 Untreated, these lesions carry an inherent high risk of subarachnoid hemorrhage. Furthermore, untreated ruptured dissecting aneurysms have a high propensity for rehemorrhage, with rates ranging from 30% to 70%.^11,12

Previous authors have demonstrated the feasibility and success of surgical or endovascular occlusion of the intracranial vertebral artery with low rates of ischemic or thromboembolic complications.^4,13 The favorable safety profile demonstrated in our study of 59 patients is consistent with these studies as well as a recent report by Kansagra et al,¹⁴ in which 100 traumatic arterial cervicocerebral vascular injuries were endovascularly treated with a low rate of immediate or delayed neurovascular complications.

The potential adverse consequences of ligation of the vertebral artery are not insignificant. Symptoms of vertebrobasilar stroke include vertigo, nausea, vomiting, headache, visual field deficit, diplopia, pupillary abnormalities, ophthalmoplegia, agnosia, and alexia without agraphia. More significant deficits such as facial paralysis, dysarthria, sudden deafness, lower cranial nerve deficits, altered awareness, Wallenberg syndrome, or Foville syndrome may also occur.^15,16

Endovascular Occlusion

Demonstration of the confluence of both vertebral arteries at the level of the vertebral junction and the anatomic potential for retrograde filling of the PICA on the affected side was paramount in establishing the feasibility of unilateral therapeutic vertebral artery occlusion. Dominance of the affected vertebral artery did not affect our decision to perform the occlusion when the need for occlusion of the affected vertebral artery was clinically imperative. When the dominant vertebral artery was already occluded or near-occluded, intact neurologic examination findings demonstrated that the patient was already tolerating a functional test occlusion. In fact, it was our observation of several neurologically intact patients who presented with acute traumatic occlusion of the dominant vertebral artery that led us to believe that therapeutic occlusion of even the dominant vertebral artery could be performed safely on the basis of anatomic criteria without antecedent balloon test occlusion.

Preservation of flow into the PICA on the affected side is an essential component of therapy. Unlike reports describing endovascular treatment of dissecting intracranial vertebral artery aneurysms, most therapeutic occlusions in our series were performed for vertebral artery pathology located several cervical vertebral segments proximal to the origin of the PICA. In some cases, collaterals distal to the site of pathology already reconstituted the distal cervical vertebral artery and filled the PICA in an antegrade fashion before proximal or segmental vertebral artery occlusion. Without such cervical collaterals, the ipsilateral PICA was typically opacified by retrograde flow from the vertebrobasilar junction even before vertebral artery occlusion.

In the setting of a severe vascular injury, such as vertebral artery fistula or frank extravasation, proximal occlusion of the vertebral artery alone is insufficient treatment because the lesion will continue to derive flow from the patent distal cervical vertebral artery in retrograde fashion. Occlusion both proximal and distal to the lesion must be secured in such cases. In many instances, it is possible to advance a catheter or microcatheter beyond the level of the lesion in antegrade fashion to perform an initial distal occlusion. Proceeding in retrograde fashion, one can use coils, glue, particles, or balloons to occlude the vertebral artery at and below the level of the pathology.¹⁷ In the case of a fistula or frank extravasation, embolic materials may also be placed outside the arterial lumen, as long as sufficient care is taken to avoid venous migration. When the proximal segment of the affected vertebral artery is already completely or near-completely occluded, coils can be placed distal to the level of injury by navigating a microcatheter through the contralateral vertebral artery, across the vertebrobasilar junction, and retrograde to the level of vascular injury (Fig 3).¹⁸

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Fig 3.

A 45-year-old man with fracture and diastasis of the right C4–C5 facet joint, with fracture extending through the right C5 transverse foramen, following a motorcycle collision. A, Anteropostior DSA of the left VA shows retrograde flow down the distal right VA due to proximal occlusion. B, A microcatheter was passed from the left VA to the vertebrobasilar junction, and retrograde microcatheterization of the right VA was performed. Hand-injection DSA demonstrates thrombus (arrow) in the lumen. C, Anteroposterior DSA with injection of the microcatheter following placement of coils above the thrombus to prevent embolization.

Regardless of the level or degree of vertebral artery pathology, the technique of occlusion must be designed to maintain the patency of the PICA origin and the vertebral artery contribution to the anterior spinal artery on the treatment side. Reconstruction of the injured segment should always be considered before vertebral artery occlusion, especially when the injured vessel is markedly dominant. However, neurologic sequelae from unilateral vertebral artery occlusion are unlikely in the presence of a normal contralateral vessel and in the absence of angiographic demonstration of branches to the spinal cord.¹⁹

Vertebral Artery Balloon Test Occlusion

While it is tempting to believe that balloon test occlusion of a vertebral artery may predict the possibility of posterior circulation stroke after permanent vertebral artery occlusion, the utility of vertebral artery balloon test occlusion has only been reported in small series,^1,2 none of which attest to the reliability or validity of vertebral artery test occlusion in predicting subsequent stroke after permanent vertebral artery occlusion. While it is clearly evident that a failed test occlusion predicts a poor outcome after permanent occlusion, there are no quantitative data to suggest that the converse is true and that passing a BTO before permanent vertebral artery occlusion diminishes the risk of subsequent posterior circulation stroke. Nevertheless, several authors prudently recommend that balloon test occlusion be performed before permanent occlusion in certain circumstances, including a contralateral vertebral artery that does not communicate with the vertebrobasilar junction, the presence of a markedly hypoplastic contralateral vertebral artery, or anticipated occlusion of a strongly dominant vertebral artery.

In a series of 23 patients with dissecting aneurysms of the vertebral artery, Albuquerque et al¹³ suggested that “dominance of the affected artery complicates the treatment paradigm. In such cases, balloon test occlusion is helpful in assessing the risk of stroke after vessel sacrifice.” Only anecdotal references are provided to support this recommendation, and balloon test occlusion was only performed in a single patient in whom the affected artery was dominant. Hoshino et al⁴ reported a series of 15 patients in whom no ischemic complications were demonstrated following ligation of the nondominant or codominant cervical vertebral artery. Although the authors suggested that angiographic test occlusion of the involved vertebral artery should be performed before permanent occlusion, only anecdotal support was provided for this recommendation. In their series, BTO was performed in a single patient who had a single vertebral artery, and the patient predictably became symptomatic during the BTO procedure.⁴

Luo et al²⁰ treated 10 patients with spontaneously ruptured vertebral dissecting aneurysms and proposed that sudden occlusion of the vertebral artery carries a risk of ischemia “particularly in patients who have a hypoplastic contralateral vertebral artery,” and that “balloon occlusion test (BOT) is essential to determine the adequacy of collateral circulation from the contralateral vertebral artery or posterior communicating arteries.” This determination was made despite any substantial evidence; however, the authors concede that “although BOT in the vertebrobasilar system is less effective in predicting future ischemia, it can indicate the extent of collateral circulation in the vertebrobasilar system.” Similarly, Rabinov et al³ described 26 patients with intracranial vertebrobasilar dissecting aneurysms who were treated by endovascular techniques. Although only 7 patients were evaluated with preprocedural BTO and no patients were reported to have failed BTO, the authors concluded that “BTO may be of benefit to determine if the collateral circulation is limited anatomically or compromised by vasospasm.”³ Despite the cautionary statements found in these articles, there are no published reports, to our knowledge, of a patient failing to tolerate vertebral BTO when the contralateral vertebral artery was documented to be patent to the level of the vertebrobasilar junction.

On the other hand, the literature demonstrates that patients who tolerate BTO of a unilateral vertebral artery may nevertheless experience ischemia and infarction after permanent vertebral artery occlusion. Sorteberg et al² have demonstrated the use of transcranial Doppler sonography to evaluate blood velocity and blood flow direction in the P1 segments during BTO to rapidly predict hemodynamic outcome at a risk comparable with that of conventional neuroangiography. Reversal of flow in the P1 segment following balloon inflation suggested that the patient was likely to tolerate permanent occlusion of the affected vertebral artery. Although all 7 patients who underwent unilateral VA BTO with transcranial Doppler in their study passed the test occlusion, a single patient developed Brown-Sequard syndrome due to medullary infarction after subsequent permanent occlusion of the intracranial VA just proximal to the origin of the PICA. The authors stated that spinal medullary branches may be too small to visualize during angiography and BTO cannot reliably exclude the risk of occlusion of a spinal medullary branch.² However, infarction in this case occurred subsequent to occlusion of the intracranial segment of the vertebral artery, where the potential for segmental cervical muscular collaterals to reconstitute the distal vertebral artery is absent. Delayed ischemic events, despite uneventful balloon test occlusion, have been described by other authors and may be related to hypoperfusion not predicted by BTO.¹

Overall, BTO does not enhance the safety of subsequent occlusion of a unilateral vertebral artery, regardless of the reason or vessel size, if there is anatomic potential for filling of the ipsilateral PICA and there is no major vascular supply to the spinal cord arising from the target segment of the affected vessel.

Alternative Treatment Strategies/Conservative Therapy

Despite the lack of complications in our series, traditional alternatives to vertebral artery occlusion, such as systemic anticoagulation or antiplatelet therapy, are adequate treatment in many patients.^21⇓–23 Biffl et al²⁴ reviewed the presentation, treatment, and outcome of 38 patients presenting with 47 blunt vertebral artery injuries during a 3.5-year period. The incidence of posterior circulation stroke was 24%, and death attributable to vertebral artery injury was 8%. They determined that systemic heparin therapy was effective in preventing stroke, neurologic deterioration, and progression to higher injury grade in patients both with and without established stroke. Additionally, dominance of the affected vertebral artery, the presence of bilateral injuries, or the initial injury grade did not appear to influence the incidence of stroke. While it has been speculated that nonocclusive injuries may be more dangerous than complete occlusions, this possibility was also not supported by their findings. The authors cautioned that anticoagulation may have resulted in complications, including hemorrhagic infarction; however, the overall benefit of systemic heparin therapy outweighed these potential complications. At our own institution, we evolved toward earlier and more frequent use of oral antiplatelet agents in patients with traumatic vascular injury in the absence of embolic sequelae. However, anticoagulation and antiplatelet therapies are not entirely benign and may still leave the patient at risk for thromboembolic events. Serious or fatal bleeding may occur, especially with multisystem trauma, and may be difficult or impossible to control.