Pearls & Oy-sters: Bow hunter syndrome: A rare cause of posterior circulation stroke

Abstract

PearlsBow hunter syndrome (BHS) is an uncommon cause of vertebrobasilar insufficiency that results from occlusion or injury to the vertebral artery (VA) during neck rotation.The cause is often a bony abnormality that may compress the VA compromising distal flow or lead to vessel wall injury resulting in thromboembolism. Oy-stersPosterior circulation strokes in young individuals should alert the neurologist to suspect BHS, especially if high cervical spine abnormalities are detected on initial head imaging.Dynamic occlusion of the VA may not be evident on angiography if a thromboembolic mechanism such as a pseudoaneurysm is involved.A 24-year-old man with no relevant medical history presented to our institution with a week of intermittent dizziness exacerbated by turning his head to the left. He acutely developed diplopia and disorientation on the day of presentation to the emergency room. He reported similar complaints a month prior. There was no history of fevers, rashes, headache, or neck trauma. There was no family history of similar complaints, vascular or connective tissue diseases, strokelike episodes, seizures, or early-onset dementia. Examination demonstrated mild impairment of cognition and a right hemiparesis. Initial head CT revealed congenital atlas nonunion (C1) with fusion of the second and third vertebral bodies (C2-C3). Brain MRI revealed diffusion restriction in the left thalamus and bilateral dorsal midbrain indicative of multiple acute infarctions. Chronic infarctions were also present in the right cerebellum, which indicated prior episodes of ischemia. A series of dynamic X-rays showed malalignment of the lateral masses of the atlas with C2, but there was no evidence of instability. CT angiography (CTA) revealed the presence of a pseudoaneurysm of the right VA at its exit from the C2 transverse foramen. This was suspected to be the source of the posterior circulation emboli. Left VA was unremarkable. There was no evidence of VA dissection on CTA (figure). Magnetic resonance angiography (MRA) with fat-suppressed images of the neck was not performed. The rest of the workup including complete blood count, serum chemistry and lipids profile, glycosylated hemoglobin levels, liver function tests, hypercoagulability studies, D-dimer levels, transthoracic echocardiography, and short-term Holter monitoring were unremarkable. A transesophageal echocardiogram was not performed because of concerns for further neck manipulation.A clinical diagnosis of BHS was made. Aspirin was initiated for secondary stroke prevention and the patient was referred for an evaluation for corrective cervical spinal surgery. Approximately 1 week later, the patient returned to an outside hospital with new cerebellar infarcts. Digital subtraction angiography (DSA) confirmed a right VA pseudoaneurysm that was suspected to have been caused by repetitive mechanical injury to the right VA from his congenital cervical spinal abnormalities during neck rotation. Dynamic occlusion of the VAs could not be reproduced

Case Report: Bow Hunter's Syndrome Caused by Compression of Extracranially Originated Posterior Inferior Cerebellar Artery

“…Hence, the atlantoaxial rotary subluxation might be one of the causes for BHS due to stenotic change at the FIA remnant. Cervical degenerative change and/or congenital abnormalities are believed to cause BHS ( 10 ). In our patient, degenerative spial change was suspected to have caused BHS by affecting the congenital vascular anomaly, given that BHS emerged at an older age.…”

Bow hunter’s syndrome due to an embolic mechanism: illustrative case

“…Most cases have permanent neurological deficits and are diagnosed at the time of recurrent strokes. Although the dominant-side VA is commonly affected in BHS with hemodynamic insufficiency, 2 , 3 involvement of the nondominant-side VA can also be a cause of BHS due to an embolic mechanism. These characteristic discrepancies between conventional BHS and BHS due to an embolic mechanism might be explained by their difference in the underlying pathology.…”

“…It has been postulated that repeated neck rotation and VA compression against the surrounding structure may cause injury to the vessel wall, which leads to direct injury of the intimal lining, arterial dissection, or pseudoaneurysm formation, resulting in subsequent thrombus formation and distal embolism. 3 , 4 …”

Dynamic CT angiography of the head and neck in the diagnosis of Bow Hunter's Syndrome: A case report

“…BHS is rare and is divided into primary and secondary BHS subtypes. Osteophyte and bone spur are the most common cause of primary BHS [3] . Secondary BHS arises due to complications in surgeries such as aortic arch replacement, aneurysm operation, head and neck trauma, and movement [4] .…”