Patients
This was a retrospective multicenter study of patients with ABAO who underwent magnetic resonance imaging (MRI) before MT in multiple hospitals in Chiba Prefecture. All study protocols were approved by the Institutional Review Board (IRB) of the Chiba University Graduate School of Medicine (approval no. M10386). A total of 10 neurosurgical centers participated in this retrospective study, and the IRBs of all 10 participating centers approved the study protocol. Given that the design of this study was noninvasive and retrospective, the requirement for informed written consent from included patients was waived.
We evaluated the data from patients who presented with ABAO and were treated with mechanical thrombectomy at all 10 hospitals between July 2014 and June 2022. The indications for mechanical thrombectomy for acute basilar artery occlusion were: 1) acute occlusion of the basilar artery confirmed by magnetic resonance (MR) angiography and 2) a National Institute of Health Stroke Scale (NIHSS) score of ≥ 6. Other indications were dependent on each hospital. The exclusion criteria were as follows: (1) MR imaging was not performed before MT (2) modified Rankin Scale (mRS) before MT was ≥ 4; (3) loss to follow-up.
Ethics approval and consent to participate
This study was conducted in accordance with the Declaration of Helsinki. Our study was approved with a waiver of the requirement for informed consent by Research ethics committee of the graduate school of medicine, Chiba university.
Mechanical thrombectomy
Each center could decide on the strategy for revascularization and select the devices deemed most appropriate for treatment. During the study period, the usable stent retrievers were second-generation stents, such as Solitaire (Covidien, Irvine, CA) or Trevo (Stryker, Fremont, CA). The usable aspiration devices were the Penumbra System (Penumbra, Oakland, CA), Sofia System (Microvention, Aliso Viejo, CA), React System (Covidien), and Catalyst System (Stryker).
Endpoint
The primary outcome of the present study was a miserable outcome at 3 months. The functional outcome was evaluated using the modified Rankin Scale (mRS) 3 months after treatment. A miserable outcome was defined as an mRS score of 5 or 6. Furthermore, factors associated with miserable outcomes were analyzed for background characteristics, MR imaging characteristics, and treatments. Univariate analyses were performed using a control group of patients with an mRS score of ≤ 4. Background characteristics were patient age, sex, past history, NIHSS score on admission, and stroke type. MR imaging characteristics were posterior circulation Acute Stroke Prognosis Early CT score (pc-ASPECTS 5, brain stem score (BSS) 6, Pons-Midbrain and Thalamus (PMT) score 7, and transverse diameter of brainstem infarction. The transverse diameter of the brainstem infarction was measured using Synapse version 3.2.0 (FUJIFILM Medical System USA's Synapse PACS System, USA). The infarct area was defined as the high-intensity area on diffusion-weighted imaging (DWI). Representative cases for measuring the transverse diameter of brainstem infarctions are shown in Figure 1. Treatments were the use of recombinant tissue plasminogen activator (rtPA), types of revascularization devices used, number of passes required, modified Thrombolysis In Cerebral Infarction (mTICI) grade time from onset to recanalization (OTR), and a symptomatic intracerebral hemorrhage (ICH), which was defined as any ICH that caused neurological deterioration with an increase of ≥4 on the NIHSS.8 Successful revascularization was defined as a mTICI grade of 2b or 3.9
Statistical analysis
Statistical evaluations were performed using JMP 16.1.0 (SAS Institute Inc., NC, USA). For univariate analyses, data were compared using the Student’s t-test for continuous variables or chi-squared tests for categorical variables. To determine the predictors of a miserable clinical outcome, a forward, stepwise logistic regression analysis that included all variables with a p value of < 0.2 in the univariate analyses was performed. Statistical significance was set at p<0.05. Receiver Operating Characteristic (ROC) curves were used to determine the threshold for predicting miserable outcomes.