A case report of Bow Hunter's syndrome with intravascular ultrasound showing changing significant severe stenosis of the left vertebral artery associated with turning left.

Background: Bow Hunter's syndrome is vertebral basilar artery insufficiency caused by mechanical occlusion of the vertebral artery during head rotation. This is often due to the formation of osteophytes, herniated discs, cervical spondylosis, or tumours. However, whether the contralateral vessel is organically stenotic is not well known.

Case Summary: A 79-year-old man was referred to our department for a close examination of syncope because the transient loss of consciousness occurring when he was made to turn his head to the left was reproducibly induced and recovered when his face was returned to the normal position. The carotid massage did not induce significant bradycardia or hypotension bilaterally, and Holter electrocardiography, echocardiography, head-up tilt test, coronary angiography, and an acetylcholine stress test showed no obvious abnormalities. A 3D CT angiography was performed to investigate the possibility of vertebrobasilar artery insufficiency, as C3/4 cervical spondylosis, and the left vertebral artery was compressed by the C4 superior process osteophyte, indicating hypoplasia of the contralateral vertebral artery. Vertebral artery angiography and intravascular ultrasound (IVUS) showed moderate stenosis of the left vertebral artery, and IVUS showed a half-circumferential calcified lesion. Compared to the midline position, the stenosis worsened at the site of compression and drainage when the patient turned left downward, and a diagnosis of Bow Hunter's syndrome was made.

Discussion: Bow Hunter's syndrome is characterized by vertebrobasilar insufficiency. Intravascular ultrasound clearly showed that the lesion was not only stenotic due to compression but also had plaque growth due to continuous mechanical stimulation.