Rotational Bow Hunter’s ischemic stroke caused by post-traumatic os odontoideum in an older patient: An illustrative case

Abstract

Background

Bow Hunter’s syndrome (BHS) is a rare condition in which head rotation or extension temporarily compresses the vertebral artery (VA), reducing blood flow to the posterior circulation. Here, a 66-year-old male developed BHS when left neck rotation caused VA compression due to a congenital os odontoideum.

Case Description

A 66-year-old male presented with loss of consciousness following hyperextension/left neck rotation. Imaging revealed a chronic odontoid fracture (Anderson Type II or here likely congenital os odontoideum) with tortuosity of the right VA in the V3 segment. Notably, a posteriorly dislocated odontoid fragment caused occlusion of the dominant right VA at the ponticulus posticus, thus causing BHS. Following C1–C2 fusion, the patient’s symptoms resolved.

An

A66-year-old male who sustained cervical hyperextension/left rotation at the C1–C2 level developed occlusion of the right VA and BHS due to an os odontoideum.

INTRODUCTION

Bow Hunter’s stroke (BHS) is a rare osteogenic vascular occlusive disorder caused by vertebral artery (VA) compression during head rotation. Here, a 66-year-old male developed BHS when he developed dominant right VA occlusion due to an os odontoideum (OS).

ILLUSTRATIVE CASE

A 66-year-old male presented with transient loss of consciousness following cervical hyperextension/left neck rotation; he was neurologically intact. Diffusion-weighted magnetic resonance (MR) imaging revealed no acute cranial ischemic changes. However, the cervical MR T2 study revealed a high-intensity intramedullary spinal cord lesion at the C1/C2 level with a significant reduction of the atlantoaxial dislocation (AAD) attributed to a likely odontoid fracture/os odontoideum, while the MR angiography showed no VA compromise on either side [Figures 1a and b]. Notably, the lateral X-ray and three-dimensional-computed tomography studies revealed posterior dislocation of a chronic odontoid fracture (i.e., likely os odontoideum) [Figures 1c and d] with intrusion on the ponticulus posticus [Figure 1e]. Due to recurrent vascular compromise in a cervical collar, the patient required a C1/C2 posterior fusion; he remains asymptomatic 1 year later [Figures 2a and b].

Figure 1:

(a) Sagittal T2-weighted magnetic resonance images of the cervical spine showing atlantoaxial dislocation and intramedullary high-signal changes. (b) Magnetic resonance angiography revealed no vertebral artery obstruction, stenosis, or dissection. (c) A preoperative lateral cervical radiograph and (d) cervical computed tomography showed an os odontoideum with incomplete odontoid process formation. (e) Three-dimensional computed tomography indicated posterior dislocation with a chronic odontoid fracture (circle) and ponticulus posticus formation (arrow).

Figure 2:

(a) Lateral radiograph and (b) three-dimensional computed tomography after posterior atlantoaxial fixation using the notch method.

DISCUSSION

BHS is a rare vascular occlusive disorder caused by VA compression during head hyperextension/rotation.[5] In this case, BHS resulted from AAD caused by post-traumatic OS (i.e., the odontoid process separated secondary to a type II fracture or, in this case, a likely os odontoideum).[11] In a review of 279 OS cases, 84.9% exhibited pyramidal signs, with 40.1% having a history of trauma. Of 260 surgically treated OS cases, only 3.8% (10/260) involved patients over 40 years old, with most cases occurring between the ages of 10 and 20 years.[3] To date, 18 cases of BHS caused by os odontoideum (including the present case) have been reported.[1,6,2,8-11] However, in cases of BHS with post-traumatic os odontoideum, older patients are more commonly affected, and transient ischemic attacks such as syncope are more frequently observed [Table 1].[1,6,9]

Table 1:

Report of the BHS with post-traumatic os odontoideum

Surgical options for BHS include (1) decompression through lateral mass opening of the atlas or axis to relieve mechanical compression on the VA,[4] (2) posterior atlantoaxial fixation,[5] and (3) endovascular treatments, such as stent placement or parent artery occlusion, may be used in certain cases to address vascular insufficiency.[7] In the present case, the odontoid process was posteriorly dislocated, and hyperextension/leftward head rotation compressed the dominant right VA at the ponticulus posticus, leading to BHS. Therefore, posterior atlantoaxial fixation was warranted to stabilize the atlantoaxial joint.

CONCLUSION

A 66-year-old male who sustained cervical hyperextension/left rotation at the C1–C2 level developed occlusion of the right VA and BHS due to an os odontoideum.

Ethical approval

The Institutional Review Board approval is not required.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

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