Management of symptomatic vertebrobasilar dissection: What is the current role for endovascular therapy and stents?

The mortality rates from acute vertebral artery dissection (VAD) vary between 70% and 95%. ¹ Cervical arterial dissections arise spontaneously or secondary to trauma-like chiropractic manipulation. ² No randomized clinical trials comparing endovascular interventions with medical management for VAD are available. The initial strategy revolves around antiplatelet or anticoagulant medications. Indications for endovascular therapy (EVT) include acute rupture with hemorrhage, enlarging pseudoaneurysm, bilateral VAD with flow limitation or distal thromboembolic events, or ischemic symptoms despite medical management. ³

Mild clinical symptoms may be managed with therapeutic heparinization. ⁴ In the setting of subarachnoid hemorrhage (SAH), aggressive treatment is required to reduce the risk of rebleed and high incidence of mortality (47%) in the first 24 h. ⁴ In acute VAD with worsening neurologic deficits, emergent recanalization may be lifesaving. ⁴ A non-dominant VAD or codominant VAD is usually tolerated well. ³ Deconstructive options for non-dominant ruptured VAD include trapping or proximal occlusion.

The growing literature of clinical evidence promotes the technical feasibility of reconstructive options like stenting for stenotic VAD. Stenting across a dissected segment reinstates the normal luminal diameter and flow by excluding the new inflow zone. ⁵ The timing of EVT remains controversial. For patients within the 4.5 h window of symptom onset and no evidence of SAH, initiation of alteplase is considered safe.^3,6 Beyond this time period, anticoagulants or antiplatelet treatment are equally effective.^7,8 A Cochrane review of arterial dissections showed observational evidence stating higher mortality among patients who did not receive any antiplatelet or antithrombotic. ⁹ As per the Cervical Artery Dissection in Stroke Study (CADISS) trial, the risk of stroke was similar in patients receiving antiplatelet (1.8%–3.8%) versus anticoagulation therapy (1.2%). ¹⁰

Residual stenosis or dissecting aneurysms are not associated with a higher rate of ischemic stroke or mortality.^3,11 Although these enlarging pseudoaneurysms indicate the persistent filling of a non-healing dissection, the incidence of these aneurysms becoming symptomatic or increasing in size is very low (<4%).^12,13 EVT is an option for patients experiencing recurrent ischemic stroke despite medical management. The reported post-procedural recurrent stroke rates are very low (0.27%).^3,14

In patients with SAH, EVT reduces the risk of rebleed and improves survival. ¹² There is lack of evidence on the role of EVT or surgery in patients with VAD presenting with headache or dissecting aneurysm alone.^12,15 The risk of stroke at 12-month follow-up was similar in patients with or without dissecting aneurysms (OR 0.84 [CI 0.1–7.31]) p  =  0.88. ¹⁰ In a meta-analysis, excellent outcomes were seen among 86.3% of EVT procedures with postoperative complications like vasospasm, rebleed or ischemia in 10.5% and an overall mortality 8.7%. This data suggested that EVT provided a comparable safety profile, a minimally invasive approach, and reduced procedure time for dissections amenable to intervention. ¹ The proximal occlusion group had poor outcome (27%) and mortality ratio (21%). ¹

Wang et al. classified types of vertebral artery (VA) dissecting aneurysms based on location (I, II, or III) relative to the origin of posterior inferior cerebellar artery (PICA) and type of circulation (a or b) based on the presence or absence of contralateral VA.^16,17 Coiling of the involved artery avoids recurrences and prevents future ischemic events in type a occlusion. In type b, the posterior circulation is dependent on the affected vertebrobasilar system. Hence stent-assisted coiling is preferred, despite the risk of early recurrence. Here follow-up angiography becomes essential, and embolization may be performed if required. Stenting of a dissected VA poses the risk of rupture during the procedure. It has been seen that thrombolysis can improve the occlusion of perforators due to thrombus in the false lumen. ¹⁷ A meta-analysis compared internal trapping with stent-assisted coiling for the treatment of VA dissecting aneurysms. ¹⁸ For ruptured aneurysms, long-term neurological outcomes were similar between internal trapping and stent-assisted coiling groups. Conservative follow-up is usually recommended for asymptomatic unruptured aneurysms. When the PICA origin is encompassed, an in situ bypass or VA-PICA stent placement with coiling may be an option. ¹⁸

The framework of a stent provides structural support to the true lumen of the dissected artery and realigns the intimal flap. In the next 28 to 96 days, the trapped subintimal hematoma undergoes gradual resorption and stent surface endothelializes. Due to the larger surface area being exposed in traumatic dissections, the thrombus formed is volumetrically bigger. This predisposes to embolic sequelae during initial stent placement. Similarly, a portion of the dissected segment may remain exposed despite attempts to cover it with a stent surface. This may create a risk for in-stent stenosis due to myointimal proliferation as well as a site from which micro-thrombi can embolize due to its exposure to the blood, leading to activation of the coagulation cascade.^3,6,19

An ideal stent design for dissected VA segments should provide enough radial force to maintain the stenotic vessel patent and have a low metal profile to abate occlusion of perforator vessels and in-stent stenosis. ²⁰ Balloon expandable coronary stents have been used in stenotic dissections at VA origin, however, their stiffness is a limiting factor for distal deployment. ³ Self-expanding open-cell stents such as Neuroform or Xpert are usually sufficient for distal dissections.^4,19 While traversing thrombotic dissections or performing angioplasty, the use of a distal protection device is recommended. Over-the-wire stents such as Wingspan provide stability during distal VA access. The Neuroform Atlas stent (Stryker Neurovascular) is a nitinol laser-cut, self-expanding hybrid stent. It offers strong wall apposition due to the distal open-cell design and stability when crossing a microcatheter is provided by the closed proximal cells. The latter feature also allows flexibility in tortuous vessels. The minimal foreshortening with stent release increases the accuracy of device placement.^6,19,21

The other reconstructive options include flow diverters like pipeline flex (PED) with shield technology, p48MW HPC, and p64 MW HPC. The PED shield provides optimum wall apposition and good reconstructive potential. ²²

Navigating the true lumen of a severe dissection or large pseudoaneurysm may be difficult. Using a microwire for sustained access of the true lumen or coaxial passage of the microwire and intermediate catheter through the proximal portion of the stent can enable the placement of a new microwire for angioplasty or additional stent placement.^3,18 In some patients with evidence of large thrombus formation, mechanical thrombectomy (MT) may be required. Using a triaxial system with proximal support can enable MT through a manual aspiration device or stent retriever.^3,14

Dual antiplatelet therapy (Aspirin 325 mg and Clopidogrel 75 mg) needs to be continued for at least 6 months in patients receiving VA stents. ²³ In case a patient was not on antiplatelets prior to stenting, a loading dose of abciximab 0.125 mg/kg followed by aspirin 650 mg and clopidogrel 600 mg and maintenance therapy thereafter is recommended.^3,23 The dosage of antiplatelets required after EVT, needs to be standardized through further clinical research.

Surgical revascularization may be technically challenging due to poor access to the vessel’s origin. In patients who are not amenable to EVT, available options include vertebral endarterectomy, bypass grafting, or transposition of the VA, to the internal or common carotid artery. Overall survival rates of 90.7% and 77.3% at 3-year and 6-year follow-ups have been demonstrated.^24,25