The HALF-IT score: proposing a simplified mechanical thrombectomy triage tool for basilar artery occlusion

Basilar artery occlusion (BAO) is a devastating subtype of stroke with poor prognosis. Current patient selection tools for endovascular thrombectomy (EVT) are multi-tiered with interrater variability and limited validation studies. The HALF-IT score is a novel, simplified, dichotomized triaging tool focusing solely on the brainstem level. This study investigated the utility of the HALF-IT score to predict functional outcomes of EVT in patients with BAO.

We conducted a multicenter, retrospective, cohort study including patients with acute BAO presenting to four comprehensive stroke centers between 2021-2025. Acute infarction of ≥50% of any brainstem section on any axial or coronal slice of MRI was considered HALF-IT positive, whereas < 50% was considered HALF-IT negative. The primary efficacy outcome was a favorable functional outcome, defined as a modified Rankin Scale (mRS) score of 0-3 at 90 days; functional independence (mRS 0-2) was analyzed as a secondary outcome. Reperfusion was graded with the modified Thrombolysis in Cerebral Infarction (mTICI) scale. Primary safety endpoints included symptomatic intracranial hemorrhage at 24 h and all-cause mortality at 90 days. Multivariable logistic regression was performed to identify independent predictors of the primary efficacy outcome.

37 patients (23 HALF-IT negative; 14 HALF-IT positive) met the inclusion criteria. The rate of 90-day mRS 0-3 was significantly lower in the HALF-IT positive compared with HALF-IT negative group [14.3% vs. 68.2%, OR 0.08 (0.01-0.45), p = 0.004]. HALF-IT positive status remained associated with a lower rate of 90-day mRS 0-3 after adjusting for age, initial NIHSS, onset-to-reperfusion time, intravenous thrombolysis administration complete reperfusion (final mTICI 3) [adjusted OR 0.02, 95% CI 0-0.84, p = 0.02]. Safety events were numerically higher in the HALF-IT positive group but the difference did not reach statistical significance. The two groups differed substantially at baseline in age, presenting NIHSS, and intravenous thrombolysis exposure, whereas stroke etiology (p = 0.28) and level of basilar occlusion (p = 0.63) were similarly distributed.

In this small, retrospective, hypothesis-generating cohort, HALF-IT positivity was associated with worse 90-day functional outcomes after EVT for BAO. Further prospective validation in larger cohorts is required before the score can inform treatment decisions.