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Bow Hunter’s syndrome: an unusual case of bilateral dynamic occlusion of vertebral arteries

CASE DESCRIPTION A 54yearold man came to our attention complaining of occasional tinnitus and blurred vision for 2 years, particularly when driving, the symptoms were linked to rightward head rotation. Neurological examination highlighted the occurrence of the reported symptoms at the neck right torsion beyond 45° after about 10 s. After a preliminary Echocolour Doppler, the patient underwent a dynamic contrastenhanced MR angiography (CEMRA) of the supraaortic trunks. In a neutral position, vertebral artery (VA) blood flow and calibre were regular with no evidence of dominance; scans performed a in rightward head rotation beyond 60° showed a bilateral dynamic stenosis of VAs, in particular at the C5–C6 level on the right, and at the C2 level on the left (figure 1). For diagnostic confirmation, a dynamic digital subtraction angiography (dDSA) was performed, adding selective injections of VAs at different degrees of right neck rotation. dDSA confirmed the CEMRA findings, leading to the diagnosis of Bow Hunter’s syndrome (BHS) with bilateral dynamic stenosis of VAs (figures 2 and 3). The examination also revealed the presence of a single thin posterior communicating artery, further explaining the insufficient compensatory flow. A CT scan, performed to complete the diagnosis, highlighted the presumable organic alterations underlying the syndrome. The exam revealed the reduction in calibre of the right C5 transverse foramen due to a mesial osteophytic bone spur with possible compressive action on the vessel (figure 4A,B), and the absence of a cleavage plane between the VA and the posterior surface of the left C2 foramen (figure 4C), which probably caused the vessel to be hypomobilised at that level and stretched during head rotation. Considering the substantial paucisintomaticity of the patient, we opted for conservative treatment and followup in accordance with the attending physicians.