Bow-hunter’s syndrome caused by dynamic vertebral artery stenosis at the cranio-cervical junction—a management algorithm based on a systematic review and a clinical series
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- Cornelius, J.F., George, B., N’dri Oka, D. et al. Neurosurg Rev (2012) 35: 127. doi:10.1007/s10143-011-0343-4
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Bow hunter's syndrome (BHS) is defined as symptomatic, vertebro-basilar insufficiency caused by mechanical occlusion of the vertebral artery (VA) at the atlanto-axial level during head rotation. In the literature, about 40 cases have been reported. However, due to the rarity of this pathology, there are no guidelines for diagnosis and treatment. Conservative, surgical, and endovascular concepts have been proposed. In order to work out an algorithm, we performed a systematic review of the literature and a retrospective analysis of patients, which have been treated in our institutions over the last decade. The clinical series was comprised of five patients. The symptoms ranged from transient vertigo to posterior circulation stroke. Diagnosis was established by dynamic angiography. In all patients, the VA was decompressed; one patient required additional fusion. The clinical and radiological results were good, and the treatment-related morbidity was low. The literature review demonstrated that Bow hunter's syndrome is a rare pathology but associated with a pathognomonic and serious clinical presentation. The gold standard of diagnosis is dynamic angiography, and patients were well managed with tailored vertebral artery decompression. By this management, clinical and radiological results were excellent and the treatment-related morbidity was low.
KeywordsBow hunter's syndromeCranio-cervical junctionExtrinsic vertebral artery compressionVertebro-basilar insufficiencySurgeryTherapy
Bow hunter's syndrome (BHS) is defined as symptomatic, vertebro-basilar insufficiency caused by mechanical occlusion of the vertebral artery (VA) at the atlanto-axial level during head rotation. The term was coined by Sorensen in 1978 based on observations in a patient becoming symptomatic during archery . In this patient, the management was conservative . Meanwhile, about 40 similar cases have been reported in the literature . However, due to the rarity of this pathology, there are no guidelines for diagnosis and treatment. Conservative, as well as surgical and, more recently, endovascular concepts have been suggested.
In the present paper, we report our experience with the surgical management of five patients treated over more than one decade. Additionally, and based on a thorough review of the literature, we carefully suggest a management algorithm.
Material and methods
First, a retrospective analysis of patients with Bow hunter's syndrome who were treated over the last decade in two tertiary care centers with special interest in cerebro-vascular pathology was performed. The medical records and neuro-imaging data were analyzed. Second, an extensive review of the literature was conducted based on Medline. We searched for articles in English language but without time restriction and using the following key words: vertebral artery, compression, rotational/ positional occlusion, vertebro-basilar insufficiency, Bow hunter ('s) syndrome/ stroke.
Patient's characteristics, treatment, and outcome
Patient number, sex, age [years]
Past medical history
Time to diagnosis [months or years]
Outcome at last follow-up
Ataxia, vertigo, nausea, hemiparesis, gait disturbance, bilateral pyramidal tract signs, ↑ when head to the right
Bony malformation C1C2 with stenosis at left for. transv. of C2
Fibrous band C1C2
Bilateral VA loops at C4C5
Vertigo, nausea, nystagmus, torticollis (with head bended to the right and turned to the left), ↑ when head bended to the left
Bony malformation C0C1
Vascular decompression, posterior bilateral
Symptom free after 7
Bilateral bony compression of VA at sulcus of atlas
Neck pain and loss of consciousness during extreme head rotation (to either side)
Bilateral bony stenosis at for. transv. of C2
Vascular decompression, antero-lateral bilateral
Fibrous band on left
Right-sided VA duplication passing through two distinct foramina (aberrant course)
Vertigo, during rotation to the right and head extension, loss of consciousness during extreme movement
Fibrous band at sulcus of atlas
Vascular decompression, left antero-lateral
Car accident, chiropractic manoeuvre
Neck pain, visual impairment, dysphasia; dizziness, dysphagia, 6–8/month
Fibrous bands C1C2
Vascular decompression, left antero-lateral
Residual psychosomatic symptoms
Diagnosis was established in all patients by dynamic digital subtraction angiography (dDSA). This allowed assessment of the vertebral artery filling during defined head movements (rotation, flexion/ extension, and lateral bending). In all patients, an extrinsic VA compression could be documented for the head position, which induced the syncope. The compression site was always located at the atlanto-axial level. In all cases, the compressed VA was the dominant one, and head rotation towards the contra-lateral side provoked the occlusion. Furthermore, posterior communicating arteries were generally hypo- or aplastic providing no collateral flow from the anterior circulation. Four patients were operated on by an antero-lateral approach and decompression of the VA was realized; in one patient (#3), a bilateral approach was realized because of a complex combined vascular and bony malformation. One patient (#2) was decompressed via a posterior approach, and simultaneous occipito-cervical fusion (C0–C2) was performed because of a pre-existing instability. No serious complication was encountered. All patients improved clinically and became free of syncopes. Early control dDSA confirmed good permeability of the decompressed arteries even in extreme rotation.
Illustrative case (patient #5)
Etiology and pathophysiology
Based on the original description by Sorensen, Bow hunter's syndrome is defined as symptomatic vertebro-basilar insufficiency by mechanical occlusion of the vertebral artery at the atlanto-axial level during contra-lateral head rotation . A similar clinical presentation may occur in case of a subaxial stenosis of the vertebral artery with ipsilateral head rotation [2, 8, 12, 17, 28, 32, 42]. Because pathogenesis and treatment strategy differ between these two entities, the latter were not the focus of the present article. However, for clear distinction, we suggest to introduce the terms atlanto-axial BHS and subaxial BHS. Finally, a mixed type may be distinguished, consisting of a bilateral VA stenosis, one at C1/C2, and the other at the subaxial level as in one case reported by Kimura et al. .
Numerous etiologies have been reported for VA compression at the atlanto-axial level, such as bony and/or vascular malformation [3, 26, 34, 36, 40], constriction at the dural entry point , instability , trauma (e.g., sport, accident, chiro-practice) , degeneration (e.g., spondylosis) , and systemic diseases (e.g., M. Paget, rheumatoid arthritis) . In some cases, the etiology was supposed to be “idiopathic”; however, intra-operative exploration found “fibrous bands” constricting the VA [12, 19, 20, 26, 28, 30]. Those bands are thought to develop from fibrous transformation of small neck muscles or be part of thickened atlanto-axial membrane. Sometimes, they are the only pathological intra-operative findings such as in one patient of our series (patient #5).
Generally, VA compression due to congenital bony anomaly presents in the pediatric population. Other etiologies, which are acquired, may present later on.
The vascular pattern typically comprises a dominant VA which is compressed at the C1/C2 level by contra-lateral head rotation. Exceptionally, compression in a non-dominant VA ending as PICA has been reported . Typically, in all cases, there is no collateral flow through the anterior circulation.
Although clinical presentation of BHS is typical for vertebro-basilar insufficiency, the diagnosis may sometimes be delayed. The pathognomonic finding is that the symptoms occur during head rotation and extension and disappear when the head is turned back into neutral position.
Once BHS is clinically suspected, the mainstay of diagnosis is dDSA [3, 4, 26, 29]. A vertebral angiogram with the head turned into stress position (contra-lateral rotation and extension) will unequivocally prove the occlusion (Fig. 1b). A four-vessel cerebral angiography is important to assess anatomical variations, collateral flow, and eventually associated stenosis [13, 14, 23, 26]. This may be preceded by non-invasive examinations, such as magnetic resonance imaging (MRI) to document any ischemic event and computerized tomography (CT) and its variants (3D-CT and CT angiography). In our experience, CT angiography with reconstructions has given very precise information about compressing elements and the topographical relationships between artery and bone [31, 43, 44] (Fig. 1a). A dynamic cervical radiography may disclose any instability. Furthermore, pre-operative transcranial Doppler sonography (TCD) [24, 42] and electro-physiological examinations (brain stem auditory evoked response (BS-AER), motor-evoked potentials (MEP), somato-sensory-evoked potentials (SSEP)) may be valuable and serve as base-line for intra-operative monitoring .
Literature overview of surgically treated patients with atlanto-axial Bow hunter's syndrome
Number of patients
Yang et al. 
Hanakita et al. 
Vascular decompression, posterior
Shimizu et al. 
Vascular decompression, posterior
Vascular decompression, antero-lateral
9 vascular decompression, posterior, 9 C1/C2 fusion
Vascular decompression, anterior
Vascular decompression, posterior
Netuka et al. 
Vascular decompression, posterior
Cornelius [present article]
4 vascular decompression, antero-lateral 1 decompression, posterior + fusion
In our experience, only one patient (#2) was treated by a posterior approach. The VA was decompressed, and simultaneously, an occipito-cervical fusion was realized because the patient harbored a pre-existing instability. The posterior route, which was used in 50% of the surgically treated cases in the literature, achieved very good results except for a 33.3% failure rate after 2–3 months reported by Matsuyama et al. [30, 33, 37]. The authors hypothesized that adhesion of the VA with surrounding soft tissues might be responsible of those failures. However, it is important to note that a peri-vascular scarring phenomenon was not observed in any other reported case of decompression. Maybe other reasons such as antero-lateral bands unreachable from a posterior approach—such as discussed above—may better explain such failures. These facts underline the tremendous importance of intra-operative or early postoperative control of surgical efficacy.
A completely different concept from vascular decompression is to perform atlanto-axial fusion. The rationale is to prevent extreme head rotation and consequent compression of the vertebral artery [9, 10, 30, 45]. This was first described in a case of BHS due to an odontoid defect inducing instability . Later, Matsuyama et al.  fused another nine patients, even without instability because he had experienced failures after vascular decompression as discussed above. The fusion technique achieved excellent relief of the vascular compression syndrome; however, the restricted head mobility has been reported as bothersome and is therefore—according to our opinion— not the treatment of first choice.
Among others, we think that fusion should be reserved for cases, where atlanto-axial instability is the main factor of vertebral artery compression. Because of frequent VA anomalies in BHS patients, the perforation risk with screw techniques is expected to be higher in this population. Therefore, screw positioning as described by Harms and Melcher  seems safer than transarticular techniques. Alternatively, various screw-less techniques may be considered.
Independently of the surgical technique, the surgical efficacy has to be controlled by early dDSA (Fig. 1f). Some authors have reported the use of intra-operative Doppler sonography, angiography, or videoangiography with indo-cyanine green (ICG) as helpful [6, 41, 42]. In one patient, we used a transcranial Doppler in order to monitor the basilar artery flow throughout the operation. This allowed confirming the efficacy of the decompression of the VA during passive head rotation, intra-operatively.
In case of bilateral vertebral artery stenosis, one at C1/C2 and the other at a subaxial level on the contra-lateral side, stenting of the latter was suggested [23, 39]. However, in those reports, the conclusions were conflicting. Whereas Horrowitz stated that their experience with stenting in this location has not been favorable, Sugiu reported a good result at the 6-month follow-up [23, 39]. At present, no conclusion, especially concerning long-term follow-up, may be drawn due to lacking data. Theoretically, vascular damage at the nondecompressed atlanto-axial level may further progress and ultimately result in cerebro-vascular stroke.
In a considerable number of reported BHS cases, the treatment was conservative. This included avoidance of head rotation, cervical collars and/or anticoagulation therapy [18, 23, 38, 43]. As no systematic follow-up has been reported, the long-term outcome cannot be assessed. One drawback of these options is a limitation of patient's quality of life.
As we lack exact data about the natural history of Bow hunter's syndrome, treatment recommendations have to be careful. However, as there is a potential life-threatening risk of posterior circulation infarction, we would generally recommend active treatment. We consider surgery as the treatment of choice, because it is a causal treatment. If performed in a center with competence in vascular and complex spinal procedures, the surgical risks appear to be acceptable. However, conservative options may be considered as alternative, if the patient is inoperable (age, co-morbidities) or not willing to accept surgery.
The present analysis based on a clinical series and a systematic review of the literature demonstrated that Bow hunter's syndrome is a rare pathology but associated with a pathognomonic and serious clinical presentation. The gold standard of diagnosis is dynamic angiography, and patients were well managed with tailored vertebral artery decompression. By this management, clinical and radiological results were excellent and the treatment-related morbidity was low.
We would like to thank Lili Laleva for the art work and Tad Dobrowolski for linguistic help.