Saurav Das, MD

Kwak HS, Park JS. Mechanical Thrombectomy in Basilar Artery Occlusion: Clinical Outcomes Related to Posterior Circulation Collateral Score. Stroke. 2020;51:2045–2050.

The successful endovascular treatment (EVT) trials for large vessel occlusion (LVO) strokes have excluded patients with basilar artery occlusion (BAO). Recently, the results of the Basilar Artery International Collaboration Study (BASICS) were presented at the European Stroke Organization (ESO-WSO) virtual platform. The results, even though underpowered to show significant benefits of EVT <6 hours of BAO, were effective in patients with moderate to severe deficits (NIHSS > 10). The trial results have shifted the spotlight to the distinction in the neuro-anatomy of posterior-circulation vessels and collateral circulation in this part of the brain, etio-pathological mechanisms involved in large vessel disease in the posterior circulation, as well as appropriate patient selection based on symptom severity and time window from symptom onset. In this blog, I will discuss a retrospective study from South Korea relevant to this topic that was published in the July issue of Stroke.

In this study, the authors present data from 81 patients with acute BAO treated with EVT using manual aspiration or stent retriever at their institute in South Korea over a period of eight years from 2012 to 2019. Posterior circulation collaterals were graded using the Basilar Artery on CT Angiogram (BATMAN) score and posterior circulation collateral score (PC-CS). Both these scoring systems have a maximum possible score of 10 points. 64% of these patients achieved TICI 2b or 3 recanalization within a median time of 5.5 hours from symptom onset, and 37% of patients had good functional outcomes defined by a 3-month modified Rankin scale ≤ 2. When compared to patients with poor outcomes, the ones with favorable outcomes had lower baseline NIHSS (15 vs 7.5, p<0.01), a greater proportion of distal BAO (20% vs 63%,  p<0.01), and better posterior circulation collateral scores (5 vs 6,  p<0.01). The authors also compared these groups on a timeline of < 3hrs, 3-6 hrs, 6-12 hrs, and >12 hrs from symptom onset. Interestingly, the time to recanalization from symptom onset was not significantly different between the groups. Receptor operating characteristic (ROC) curve analysis for collateral scores yielded the highest area under the curve with a cut-off score of 6 for both BATMAN and PC-CS. Using these cut-offs, multivariate analysis revealed that NIHSS score <15 (odds ratio 8.49, P=0.004), PC-CS ≥6 (odds ratio 3.79, P=0.042), and distal BAO (odds ratio 3.67, P=0.035) were independent predictors of good clinical outcomes.

Figure 1. Schematic illustration of collateral scores.

The study is limited in being a retrospective study on a small sample size from a single center. The authors do not report Alberta stroke program early CT score (ASPECTS) or MR imaging data for these patients, as well as possible etio-pathology of the basilar artery disease. The use of EVT-device was not uniform among all patients. The results showed that lower baseline NIHSS (< 15) had good outcomes as opposed to BASICS trial that recommended benefit in patients with moderate to severe symptoms. Nevertheless, the study illuminates how the neuro-anatomy of posterior circulation could be addressed during patient selection for EVT. A distal location of BAO and good collateral status measured by BATMAN and PC-CS scores can be independent predictors of good outcomes in these patients, even when they present beyond the standard time window.