Bow hunter's stroke due to instability at the uncovertebral C3/4 joint

Abstract

Bow hunter's stroke is typically due to mechanical compression or stretching of the dominant vertebral artery (VA) during contralateral head rotation against the bony elements of the atlas and axis. We report a case of vertebrobasilar insufficiency due to bilateral vertebral artery occlusion at the left C3-4 and the right C1-2 junction on rightward head rotation. A 64-year-old man experienced ischemic symptoms during 90° head rotation to the right with complete resolution of symptoms after returning his head to the neutral position. Dynamic cervical angiography with rightward head rotation showed severe compression of the right VA at the transverse foramen of C3-4 and mechanical stenosis of the left VA at the C1-2 level. During head rotation, the flow of the right VA was decreased more than the left side. Cervical 3-D computed tomography (CT) on rightward head rotation demonstrated displacement of the uncovertebral C3-4 joint, with excessive rotation of the C3 vertebral body. Based on these findings, instability at C3-4 was suspected to be the main cause of the vertebrobasilar insufficiency. Anterior discectomy and fusion at the C3/4 level were performed. Postoperatively, the patient experienced complete resolution of symptoms, and dynamic cervical angiography showed disappearance of the compression of the right VA. To our knowledge, this is the first reported case of bow hunter's stroke diagnosed by dynamic cerebral angiography and cervical 3-D CT without angiography, and treated by anterior decompression and fusion without decompression of the VA.

Fig. 1

Preoperative cerebral angiograms of the right VA show normal flow in the neutral position (a), and severe stenosis between the transverse foramen of C3 and C4 (arrow) and decreased flow on rightward head rotation (b), and angiograms of the left VA show normal flow in the neutral position (c), and severe stenosis at the C1–2 level (arrow) and decreased flow on rightward head rotation (d)

Fig. 2

Preoperative axial cervical CT scans show no osseous structures in the transverse foramina of C3 (a) and C3/4 (b, c) or C4 (d), and 3-D CT on rightward head rotation shows displacement of the uncovertebral joint at the C3/4 level (e, ellipse)

Fig. 3

Postoperative digital subtraction angiograms on rightward head rotation show that stenosis of the right VA has disappeared at the C3–4 level (a), and there is slight residual stenosis of the left VA at C1–2 (arrow) with improved flow after the operation (b)