34.1.1 Clinical Presentation

An 86-year-old woman presented with left-sided hemiplegia and aphasia 2 hours before hospital admission. Clinically, she displayed a full right middle cerebral artery (MCA) occlusion syndrome with hemineglect, hemiplegia, and gaze preference to the left. The National Institutes of Health Stroke Scale (NIHSS) score at presentation was 24. Intravenous thrombolysis was administered after initial noncontrast CT (NCCT) of the brain confirmed no intracranial hemorrhage.

34.1.2 Imaging Workup and Investigations

CT angiography of the brain confirmed a complete right M1 MCA occlusion with moderate pial collateral vessels. The thrombus measured 8 mm in length. CT perfusion demonstrated a clear ischemic penumbra in the entire right hemisphere, with no established infarct core as defined by regional cerebral blood flow less than 30% (Fig. 34.1).

Endovascular Treatment

The patient was brought to the angio suite and transfemoral endovascular thrombectomy with conscious sedation was performed. A balloon guiding catheter (BGC; FlowGate, Stryker) was navigated to the right cervical internal carotid artery (ICA) over a 5-Fr diagnostic catheter and Terumo Glidewire. Digital subtraction angiography again demonstrated the complete right M1 occlusion just distal to the origin of the medial lenticulostriate vessels. (Fig. 34.2a) Stent-retriever thrombectomy was performed by first navigating a microcatheter (Trevo Pro 18, Stryker) to the superior M2 trunk over a microguidewire, followed by deployment of the Trevo ProVue 6 × 25 mm stent retriever across the occluding thrombus. The first pass with proximal flow reversal yielded a piece of thrombus, but control angiography demonstrated fragmentation and distal migration of the clot, resulting in occlusion of the inferior M2 trunk as well as more distal occlusion of the opercular M3 branch (Fig. 34.2b, c).

Using a similar setup, the inferior M2 trunk was recanalized by a second pass of stent retriever with proximal flow reversal at the level of the BGC. Another couple of attempts to revascularize the opercular branch was unsuccessful due to the distality of the clot and tortuous vascular anatomy. Finally, modified treatment in cerebral infarction 2a revascularization was achieved with the right opercular branch of the MCA remaining occluded (Fig. 34.2d, e). Follow-up CT scan of the brain demonstrated infarction of the right insula and the basal ganglia, correlating to the area supplied by the opercular branch (Fig. 34.2f). Patients’ neurological symptoms improved to NIHSS 15, but remained disabled with left hemiparesis and a modified Rankin scale score of 3 at discharge.

34.1.3 Discussion

Mechanical thrombectomy with newer generation devices have consistently demonstrated better rates of reperfusion; however, this has not resulted in equally high rates of good clinical outcome. ^{1 ,​ 2 ,​ 3}

The aim of mechanical thrombectomy is to reperfuse the affected territory in order to reduce, if not prevent, ischemic injury to the brain; however, when removing the clot from the affected vessel, one of the risks is the formation of emboli in a new vascular territory (ENT) and the consequent development of an infarct in a previously unaffected part of the brain. This may contribute to the discrepancy between the rates of reperfusion and good clinical outcome. In the major trials, the rate of ENT has been reported to be between 0 and 11.4% (Table 34.1). ^{1 ,​ 2 ,​ 3 ,​ 4 ,​ 5 ,​ 6 ,​ 7 ,​ 8 ,​ 9} In addition to ENT, there is also risk of emboli downstream from the originally occluded vessel; for example, Gascou et al reported this phenomenon in 3.5% of their patient cohort. ⁹ The clinical impact of these downstream emboli is not fully known; however, Kurre et al reported clinical worsening by more than 4 points on the NIHSS scale in 3 of the six patients who experienced ENT. Gascou et al reported clinical worsening among 13 of 18 patients who had ENT or emboli downstream for the occluded vessel within the same vascular territory, and Davalos et al reported that 2 of 9 patients experienced a clinically significant stroke following ENT. ^{8 ,​ 9 ,​ 10} In contrast, the two patients in EXTEND IA who experienced ENT had no clinical symptoms attributable to these distal emboli. ⁵ Rescue therapy can be performed to revascularize the newly occluded vessel as performed in six of the patients from the Kurre series; this proved to be successful in five patients, and in three out of those five patients, there was no evidence of new infarcts. ⁸ Attempts at rescue, however, mean additional instrumentation, which is associated with increased risk, as illustrated in the present case. Given that not all of these emboli are eloquent territory or clinically symptomatic, it may be that in some instances, there is no need to chase ENT. When patients are under conscious sedation, on-table examination can be performed to determine if there is a need to perform rescue therapy.

Both clot and treatment strategy factors may be considered to be related to the risk of ENT. These factors include clot composition, administration of intravenous tissue plasminogen activator (IV-tPA), location and length of the clot, thrombectomy device, and choice of access/ guiding catheter. Conceptually, longer clots that are soft, lodged across bifurcations, or angulated segments of a vessel would be more prone to fragmentation and ENT. This risk may be aggravated by the use of IV-tPA. Nevertheless, the two patients in the STAR trial who experienced ENT did not receive IV-tPA, and other studies have not shown any difference in the rate of ENT with the administration of fibrinolystics. ^{9 ,​ 10}

More importantly, the thrombectomy strategy may be crucial in preventing ENT. Although a recent meta-analysis of 2,893 patients comparing aspiration-first and stent-retriever-first thrombectomy did not demonstrate a difference in the rate of ENT, ¹¹ Chueh et al found the use of proximal flow reversal with a BGC to be most effective in preventing soft elastic clot fragmentation in in vitro studies. ¹² Kurre et al likewise observed a trend toward fewer ENT when distal aspiration was performed with distal emboli seen in 3.3% of those who underwent distal aspiration versus 14.6% who did not. ⁸ It is therefore advisable to adopt BGC or distal aspiration in conjunction with stent-retriever thrombectomy when the risk of ENT or distal emboli is high, such as in cases with embolic, long thrombus across bifurcations.