BACKGROUND
Incidence and natural history of acute bihemispheric strokes (ABS) are poorly known. Aim of our study was to identify frequency, associated factors, and outcome of a consecutive series of ABS patients from a single carotid source, focusing on the Willis' polygon morphology.
METHODS
In the ASTRAL registry (2003-­‐18), we retrospectively reviewed data from anterior ABS patients affected by carotid atherosclerosis or dissection on DWI-MRI. Overall Willis' patency or incompleteness (i.e. absence/hypoplasic A1, P1, anterior/posterior communicating arteries) was recorded. Patients with bihemispheric lesions were compared with patients with unilateral lesion in a matched 1:3 analysis for age, grade of stenosis and TOAST. A multivariate analysis was performed to identify independent factors associated with ABS.
RESULTS
Out of 186 patients with single carotid source (16% dissections), we identified 24 (13%) ABS patients. In the univariate analysis on the matched cohort, patients with ABS had lower diastolic blood pressure on admission
(73 vs. 87 mmHg, p=0.007), more frequently contralateral internal carotid (ICA) occlusion (p=0.046) and absence of anterior communicating artery (ACoA) (70% vs. 25 %, p<0.001). On multivariate analysis, contralateral ICA occlusion and absence of ACoA were independent predictors of ABS (OR=15.64; 95%CI:2.09-­ 117.25 and OR=9.19; 95%CI:2.86-­‐25.00,  respectively). ABS was associated to
higher recurrence rate (18.2 vs 4.5%, p=0.060) and worse 3‐month outcome (median mRS 3 vs 1, p=0.012).
CONCLUSIONS
Occlusion of contralateral ICA and  absence of ACoA were predictors of bilateral ischemic lesions in stroke due to single carotid artery source. These findings suggest an important role of hemodynamic mechanisms in the pathogenesis of ABS.

ACUTE BIHEMISPHERIC STROKES FROM A SINGLE CAROTID SOURCE: FREQUENCY AND RISK FACTORS