Intracranial Atherosclerotic Disease Distribution Across Circle of Willis Segments: Insights from CREST-H

BACKGROUND: The Circle of Willis (CoW) is an important collateral pathway, and its anatomy may influence intracranial flow patterns in the setting of atherosclerotic disease. This study describes the distribution of intracranial atherosclerotic disease (ICAD) and evaluates associations between ICAD presence across CoW vessel segments in the Carotid Revascularization and Medical Management for Asymptomatic Carotid Stenosis – Hemodynamics (CREST-H) cohort. METHODS: This retrospective analysis included 252 patients from the CREST-H trial with baseline Time-of-flight MR angiography (TOF-MRA) suitable for evaluation. TOF-MRA was used as a luminal surrogate to assess intracranial arterial narrowing and irregularity, rather than as a direct plaque-imaging technique. Intracranial arterial segments were assessed for luminal abnormalities compatible with ICAD, and the CoW was categorized based on circle completeness and anatomical pattern using Ayre’s classification. Phi-coefficient was used to evaluate associations in ICAD presence across vessel segment pairs. RESULTS: ICAD was most frequently observed in the right (69.4%) and left (67.1%) intracranial ICA, followed by anterior and posterior circulation CoW segments. Complete, partially complete, and fully incomplete CoW was identified in 17.5%, 73.8%, and 8.7% of patients, respectively. Pairwise associations in ICAD presence were observed between the right ICA and right ACA (ϕ = 0.25, p < 0.001) and between contralateral paired vessels, including right and left ICA, PCA and ACA (all p < 0.001). No correlation was found between left ICA and left ACA (ϕ = 0.10, p = 0.08). CONCLUSIONS: In the atherosclerosis-enriched CREST-H cohort, ICAD was common and was most frequently seen in intracranial ICAs. Associations in ICAD presence were observed between selected ipsilateral and contralateral CoW vessel pairs. These findings are descriptive and may help provide preliminary data for future studies of intracranial atherosclerotic distribution in patients with carotid atherosclerotic disease.