Background Cerebral vascular anatomy, specifically the circle of Willis (COW), plays an unstudied role in the development of stroke after blunt cerebrovascular injury (BCVI; carotid and vertebral). Variant anatomy is very common, and certain variants such as persistent fetal circulation (enlarged posterior communicating artery) may improve collateralization between the anterior (carotid) and posterior (vertebral) circulations. Identifying patients at increased stroke risk may allow tailored anticoagulation, the mainstay of therapy. This study constitutes the first attempt to identify vascular anatomy patterns associated with stroke, with the hypothesis that normal anatomy would protect against stroke.

Study design Radiographic images from patients with BCVI-related stroke from 2005 to 2014 were identified. Patients with stroke were compared with injury-matched, non-stroke controls. Normal COW anatomy is defined as the presence of all vessels without hypoplasia.

Results Of 457 patients BCVI, 22 (4.8%) BCVI-related patients with stroke and matched controls were reviewed. 9 (41%) patients with stroke and 2 (9%) controls had normal COW anatomy (OR=7.1, 95% CI 1.28 to 33.3). Persistent fetal-type circulation was found in 6 controls and 1 patient with stroke, resulting in a 7.9-fold decreased risk of stroke with this variant (OR=0.13, 95% CI 0.003 to 1.26).

Conclusions Cerebral vascular anatomy has a role in BCVI-related stroke. Normal anatomy is not protective; however, the increased collateral flow provided by a persistent fetal-type enlarged posterior communicating artery is likely protective. The identification of high-risk patients may eventually allow for more tailored treatment. Prospective, multi-institutional trials are needed to further reduce the incidence BCVI-related stroke.

Level of evidence Prognostic and epidemiological, level III.