16.3.1 Occlusion of Device and Stroke

Although uncommon, ischemic stroke is the leading cause of complications after treatment of aneurysms using flow diverters and is identified in 3 to 6% of patients. ⁴ , ²⁰ , ²¹ In the PUFS trial, the rate of acute ischemic stroke within 6 months of treatment was 6.5%. In this cohort, 2.8% of patients had stroke secondary to in-stent thrombosis or occlusion. ²⁴ The rate of stroke after 6 months was 0% in this cohort. Review of the IntrePED registry noted an incidence of 4.5% of ischemic stroke (36/793 patients with 906 aneurysms). ²⁵ In this series, 72.2% of all strokes occurred within 30 days of treatment (median, 3.5 days; range, 0–397 days), resulting in 10 deaths and 26 major neurological deficits. On multivariate analysis, fusiform aneurysm was the only predictor of postprocedural ischemic stroke. Larger fusiform aneurysms had a higher rate of complications than smaller fusiform aneurysms.

Park et al ²⁶ reported four permanent complications resulting in death or permanent morbidity in a cohort of 126 patients treated at the Barrow Neurological Institute (mortality rate of 3.2%). There were four cerebrovascular accidents in the absence of device occlusion ( Fig. 16.1), one of which resulted in death. A second patient had clot in the device and underwent uneventful clot removal. Six patients had complete occlusion of their flow diverters on follow-up imaging. Two had devastating neurological deficits as a result of occlusion and died. The remaining four had no deficits or neurological sequelae.

One noted cause of thrombotic complication is the resistance of a subset of the population to aspirin and clopidogrel. ²⁷ , ²⁸ This resistance is further complicated by lack of consistency and agreement with regard to the appropriate antiplatelet regimen after flow diverter placement. ²⁹ Tan et al ³⁰ reported thromboembolic complications in 6.8% of patients treated with a Pipeline Embolization Device (PED). In this cohort, patients with P2Y12 reaction unit values of more than 208 were more likely to have thromboembolic complications. In a meta-analysis of 19 studies, Skukalek et al ³¹ identified that the use of highdose aspirin less than 6 months post–PED deployment was associated with fewer thrombotic events than when low-dose aspirin was used. A higher rate of thrombotic events was observed with the use of clopidogrel less than 6 months post– PED deployment.

Other mechanisms of ischemia in a delayed fashion include acute and subacute in-stent thrombosis during the procedure resulting in postoperative occlusion of the stent with or without distal emboli, exacerbated by inappropriate dual-antiplatelet regimens and the bare metal nature of the stent.

16.3.2 Occlusion of Side Branches and Perforators

Occlusion of side branches or perforating vessels can cause devastating strokes when these vessels represent end vessels without redundant or anastomotic circulations. Posterior circulation aneurysms or those aneurysms with perforating vessels emanating from the diseased portion of the vessel (e.g., lenticulostriate arteries from the M1 segment of the middle cerebral artery) are at a higher risk of complication with perforator strokes. ³² , ³³ A recent meta-analysis noted a perforator infarction rate of 3.0% across all aneurysms studied and a higher rate in aneurysms in the posterior circulation. ²⁰ The higher complication rate of thrombosis in the treatment of dolichoectatic and fusiform basilar artery aneurysms with the use of flow diverters provides a cause for pause in the use of these devices for this subset of aneurysms. ³⁴ The higher complication rate in this group is likely caused by poor wall apposition of flow diverters in the setting of fusiform aneurysms. Poor wall apposition results in delayed endothelialization of stents and increased likelihood of in-stent thrombosis and embolization. Other factors include the larger size of these aneurysms, use of multiple flow diverters, and nonuniform use of dual-antiplatelet medications. ¹² , ²¹ , ³⁴ , ³⁵

Occlusion of the anterior choroidal artery can have potentially devastating complications, but fortunately it appears that anterior choroidal artery loss after flow diversion is a rare event. Brinjikji et al ³⁶ reported their experience with flow diversion for ICA aneurysms in which the anterior choroidal artery was covered by the stent. In the immediate postprocedure setting, all 15 patients in this study had patency of the anterior choroidal artery. At 6-month followup, only a single anterior choroidal artery was occluded, and this patient did not suffer any complications from the loss of this artery. In a cohort of 49 patients treated with flow diversion in whom branch vessels of the internal carotid artery were covered by the flow-diverting stents, the overall rate of branch vessel occlusion was 4% for the ophthalmic artery, 7.1% for the posterior communicating artery, and 0% for the anterior choroidal artery. None of these patients had neurological deficits secondary to the occlusion of the covered vessel. Branch occlusion was not associated with the number of flow diverters used. ³⁷ A second larger cohort of 82 patients was recently described by the Buffalo group. ³⁸ In this cohort, 127 arterial branches were covered by flow diverters. At a mean angiographic follow-up of 10 months, arterial branch occlusion occurred in 15.8% and included occlusion of the anterior cerebral arteries (n = 2), ophthalmic arteries (n = 8), and posterior communicating arteries (n = 3). There were no anterior choroidal artery occlusions in this series, and none of the patients experienced neurological deficits.

Occlusion of the ophthalmic artery in a delayed fashion has been reported, ³⁹ , ⁴⁰ although in most cases this occlusion is of no consequence because of the redundant collateral circulation provided to the territory by branches of the external carotid artery. In rare cases, occlusion of the ophthalmic artery can cause visual disturbances. ⁴¹