Bow Hunter's Stroke Caused by Cryptic Recanalization of an Occluded Vertebral Artery: A Case Report

An 80-year-old man was admitted to our hospital with acute cerebellar infarction. Conventional magnetic resonance angiography and computed tomography angiography (CTA) showed occlusion of the right vertebral artery (VA). Carotid ultrasonography revealed that the right VA was narrowed at its entry point into the transverse foramen near C6. Given the location of the VA stenosis, the blockage may have been due to compression from the cervical spine. Therefore, we assessed the right VA blood flow by moving the neck. The cervical spine was rotated left and right for evaluation; however, no blood flow was observed. The neck was then flexed 30° from the neutral position, and blood flow in the VA was confirmed using color and pulse Doppler. Similarly, CTA and cerebral angiography confirmed that the right VA, which was occluded in the neutral neck position, recanalized when the neck was flexed. We hypothesized that a thrombus had formed in the right VA during occlusion. When the neck was flexed, the right VA reopened, allowing the thrombus to move, resulting in embolic cerebral infarction. In typical bow hunter's syndrome (BHS), VA occlusion occurs in the neutral position, and blockage happens during rotation. In this case, the VA was blocked in the neutral position and recanalized during flexion. This so-called "hidden BHS," as seen in this case, is easily overlooked, highlighting the importance of careful evaluation.