Abstract
Bow hunter's syndrome (BHS) is most commonly caused by compression of the vertebral artery (VA). It has not been known to occur due to an extracranially originated posterior inferior cerebellar artery (PICA), the first case of which we present herein. A 71-year-old man presented with reproducible dizziness on leftward head rotation, indicative of BHS. On radiographic examination, the bilateral VAs merged into the basilar artery, and the left VA was predominant. The right PICA originated extracranially from the right VA at the atlas–axis level and ran vertically into the spinal canal. During the head rotation that induced dizziness, the right PICA was occluded, and a VA stenosis was revealed. Occlusion of the PICA was considered to be the primary cause of the dizziness. The patient underwent surgery to decompress the right PICA and VA via a posterior cervical approach. Following surgery, the patient's dizziness disappeared, and the stenotic change at the right VA and PICA improved. The PICA could be a causative artery for BHS when it originates extracranially at the atlas–axis level, and posterior decompression is an effective way to treat it.
Highlights
Bow hunter’s syndrome (BHS) is a transient and symptomatic vertebrobasilar insufficiency that occurs during head rotation, resulting in dizziness and fainting [1]
Computed tomography angiography (CTA) on leftward head rotation showed that the posterior inferior cerebellar artery (PICA) was severely compressed in the narrow space surrounded by the atlas and axis, and that the right vertebral artery (VA) was compressed at the axis level (Figure 2)
An embryonic remnant of the first intersegmental artery (FIA) can be associated with VA variants at the atlas–axis level, and these are classified into three types: persistent FIA, VA fenestration, and atlas–axis originating PICA [4]
Summary
Bow hunter’s syndrome (BHS) is a transient and symptomatic vertebrobasilar insufficiency that occurs during head rotation, resulting in dizziness and fainting [1]. It originates extracranially at the atlas–axis level, where it is associated with an embryonic remnant of the first intersegmental artery (FIA) [4] It enters the cervical dural sac in parallel with the C2 nerve root [5]. This extracranial PICA could be compressed by head rotation and thereby cause BHS, but this situation has never been reported. Leftward head rotation at 45◦ did not induce dizziness, but dynamic DSA showed stenosis of the right VA at the level of the axis (Figure 1D). Computed tomography angiography (CTA) on leftward head rotation showed that the PICA was severely compressed in the narrow space surrounded by the atlas and axis, and that the right VA was compressed at the axis level (Figure 2). BHS did not recur without any thrombotic therapy for 3 months after the surgery
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