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Two case presentations and surgical management of Bow Hunter's syndrome associated with bony abnormalities of the C7 vertebra

2011; Elsevier BV; Volume: 53; Issue: 5 Linguagem: Inglês

10.1016/j.jvs.2010.11.093

1097-6809

Victoria Lee, Thomas S. Riles, Jennifer Stableford, Ramón Berguer,

Neurosurgical Procedures and Complications

Bow Hunter's syndrome is a condition in which patients experience vertebrobasilar symptoms on head turn. It may be a consequence of intrinsic factors such as atherosclerosis, or it may be secondary to mechanical compression. Most commonly, this occurs at the level of C2 or above. We present two rare cases of Bow Hunter's syndrome secondary to mechanical compression at the level of C7. Discussed are the anatomic conditions leading to this syndrome in these two patients, the methodology for confirming the diagnosis, and the successful management by partial resection of the transverse processes compressing the vertebral arteries. Bow Hunter's syndrome is a condition in which patients experience vertebrobasilar symptoms on head turn. It may be a consequence of intrinsic factors such as atherosclerosis, or it may be secondary to mechanical compression. Most commonly, this occurs at the level of C2 or above. We present two rare cases of Bow Hunter's syndrome secondary to mechanical compression at the level of C7. Discussed are the anatomic conditions leading to this syndrome in these two patients, the methodology for confirming the diagnosis, and the successful management by partial resection of the transverse processes compressing the vertebral arteries. Vertebrobasilar ischemia is a condition manifested by a constellation of symptoms, one of the most common being dizziness, particularly in elderly patients.1Bulsara K.R. Velez D.A. Villavicencio A. Rotational vertebral artery insufficiency resulting from cervical spondylosis: case report and review of the literature.Sug Neurol. 2006; 65: 625-627PubMed Google Scholar, 2Horowitz M. Jovin T. Balzar J. Welch W. Kassam A. Bow Hunter's syndrome in the setting of contralateral vertebral artery stenosis: evaluation and treatment options.Spine. 2002; 27: E495-E498Crossref PubMed Scopus (27) Google Scholar, 3Bauer R.B. Mechanical compression of the vertebral arteries.in: Berguer R. Bauer R.B. Vertebrobasilar arterial occlusive disease: medical and surgical management. Raven Press, New York1984: 45-71Google Scholar, 4Kuether T.A. Nesbit G.M. Clark W.M. Barnwell S.L. Rotational vertebral artery occlusion: a mechanism of vertebrobasilar insufficiency.Neurosurgery. 1997; 41: 427-433Crossref PubMed Scopus (148) Google Scholar, 5Natello G.W. Carroll C.M. Katwal A.B. Rotational vertebrobasilar ischemia due to vertebral artery dynamic stenosis complicated by an ostial atherosclerotic stenosis.Vasc Med. 2009; 14: 265-269Crossref PubMed Scopus (13) Google Scholar Other common symptoms include nausea, dysarthria, dysphagia, transient blurring of vision in one or both eye fields, gait disturbance, headaches, and other sensorimotor findings such as tinnitus, hearing loss, syncope, or drop attacks.1Bulsara K.R. Velez D.A. Villavicencio A. Rotational vertebral artery insufficiency resulting from cervical spondylosis: case report and review of the literature.Sug Neurol. 2006; 65: 625-627PubMed Google Scholar, 3Bauer R.B. Mechanical compression of the vertebral arteries.in: Berguer R. Bauer R.B. Vertebrobasilar arterial occlusive disease: medical and surgical management. Raven Press, New York1984: 45-71Google Scholar, 4Kuether T.A. Nesbit G.M. Clark W.M. Barnwell S.L. Rotational vertebral artery occlusion: a mechanism of vertebrobasilar insufficiency.Neurosurgery. 1997; 41: 427-433Crossref PubMed Scopus (148) Google Scholar, 5Natello G.W. Carroll C.M. Katwal A.B. Rotational vertebrobasilar ischemia due to vertebral artery dynamic stenosis complicated by an ostial atherosclerotic stenosis.Vasc Med. 2009; 14: 265-269Crossref PubMed Scopus (13) Google Scholar, 6Vilela M.D. Goodkin R. Lundin D.A. Newell D.W. Rotational vertebrobasilar ischemia: hemodynamic assessment and surgical treatment.Neurosurgery. 2005; 56: 36-45PubMed Google Scholar, 7Nagashima C. Vertebral artery insufficiency and cervical spondylosis.in: Fein J.M. Flamm E.S. Cerebrovascular surgery. Springer-Verlag, New York1985: 529-555Crossref Google Scholar Bow Hunter's syndrome is an uncommon condition in which symptoms of vertebrobasilar ischemia occur secondary to occlusion of the dominant vertebral artery during head rotation.2Horowitz M. Jovin T. Balzar J. Welch W. Kassam A. Bow Hunter's syndrome in the setting of contralateral vertebral artery stenosis: evaluation and treatment options.Spine. 2002; 27: E495-E498Crossref PubMed Scopus (27) Google Scholar, 8Tsutsumi S. Ito M. Yasumoto Y. Simultaneous vertebral artery occlusion in the lower cervical spine manifesting as bow hunter's syndrome.Neurol Med Chir (Tokyo). 2008; 48: 90-94Crossref PubMed Scopus (23) Google Scholar, 9Matsuyama T. Morimoto T. Bow hunter's stroke caused by non-dominant vertebral artery occlusion: case report.Neurosurgery. 1997; 41: 1493-1495Crossref Scopus (49) Google Scholar The dominant vertebral artery is more commonly occluded at the higher cervical levels in this condition, whereas occlusion at the cervical levels below C2 is less frequently seen.8Tsutsumi S. Ito M. Yasumoto Y. Simultaneous vertebral artery occlusion in the lower cervical spine manifesting as bow hunter's syndrome.Neurol Med Chir (Tokyo). 2008; 48: 90-94Crossref PubMed Scopus (23) Google Scholar, 9Matsuyama T. Morimoto T. Bow hunter's stroke caused by non-dominant vertebral artery occlusion: case report.Neurosurgery. 1997; 41: 1493-1495Crossref Scopus (49) Google Scholar, 10Velat G.J. Reavey-Cantwell J.F. Ulm A.J. Lewis S.B. Intraoperative dynamic angiography to detect resolution of bow hunter's syndrome: technical case report.Surg Neurol. 2006; 66: 420-423Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar, 11Whitmore R.G. Simon S.L. Hurst R.W. Nisenbaum H.L. Kasner S.E. Zager E.L. Bow Hunter's syndrome caused by accessory cervical ossification: posterolateral decompression and use of intraoperative Doppler ultrasonography.Surg Neurol. 2007; 67: 169-171Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar The most common course for the vertebral artery as it takes off from the subclavian is a path between the anterior scalene and longus colli muscles, where it runs anterior to the transverse process of C7 until entering the transverse foramen of C6 (Fig 1).12Cloud G.C. Markus H.S. Diagnosis and management of vertebral artery stenosis.QJM. 2003; 96: 27-54Crossref PubMed Scopus (130) Google Scholar This pattern is seen in about 95% of the population, whereas entry of the vertebral artery into the transverse foramen of C7 is seen between 0.3% and 5.0% of the time.13Hong J.T. Park D.K. Lee M.J. Kim S.W. An H.S. Anatomical variations of the vertebral artery segment in the lower cervical spine: analysis by three-dimensional computed tomography angiography.Spine. 2008; 33: 2422-2426Crossref PubMed Scopus (76) Google Scholar, 14Bruneau M. Cornelius J.F. Marneffe V. Triffaux M. George B. Anatomical variations of the V2 segment of the vertebral artery.Neurosurgery. 2006; 59 (discussion ONS20-4): ONS20-ONS24Crossref PubMed Scopus (116) Google Scholar The transverse foramena gradually enlarge in diameter from C3 to C6: C3 being smaller than C4, C4 being smaller than C5, and C6 being the largest, while C7 is consistently the smallest. Owing to the low frequency in which C7 contains the vertebral artery—because its primary purpose is in serving as a passageway for the vertebral vein alone—this is usually of little clinical consequence.15Cagnie B. Barbaix E. Vinck E. D'Herde K. Cambier D. Extrinsic risk factors for compromised blood flow in the vertebral artery: anatomical observations of the transverse foramina from C3 to C7.Surg Radiol Anat. 2005; 27: 312-316Crossref PubMed Scopus (35) Google Scholar We describe two unusual cases of Bow Hunter's syndrome secondary to mechanical compression at the level of the C7 vertebrae. A 50-year-old man presented after a syncopal episode while backing up his car with his head turned to the right. His history was significant for a bicycle accident 20 years previously that resulted in neck pain, dizziness, and occasional syncopal events when turning his head to the left. Approximately 5 months before the date of referral, he experienced similar symptoms when turning his head to the right. He ultimately decided to seek medical attention after the syncopal episode while backing his car, resulting in an accident. The patient was originally evaluated at another hospital, where a conventional angiogram was performed, revealing moderate stenosis at the left vertebral artery takeoff. The severity of the stenosis was felt to be insufficient to fully explain his symptoms, and he was referred to our offices for further evaluation, which included a repeat angiogram and magnetic resonance angiography (MRA). The MRA demonstrated complete occlusion of his right vertebral artery at the base of the skull, most likely secondary to the trauma of the bicycle accident 20 years earlier. The left vertebral artery was noted to be patent, with a 50% narrowing at its origin from the subclavian and was the sole source of blood flow through the basilar system. An angiogram performed with the patient in the neutral position showed normal takeoff of all major vessels in the brachial cephalic vasculature. The left vertebral artery was noted to be dominant, with a 30% to 40% luminal diameter narrowing at its origin. The right vertebral artery was hypoplastic, tapering to an occlusion at the C1 level. The distal right vertebral artery above the occlusion was supplied by retrograde flow from the basilar artery. The posterior communicating arteries were small or nonexistent, resulting in an isolated posterior circulatory system. The patient's head was turned to the left, resulting in the patient complaining of dizziness and fear of losing consciousness. A repeat angiogram with the head turned left revealed a short segment near-occlusion of the left vertebral artery at the C7 level and delayed antegrade filling of the distal vertebral artery (Fig 2). A computed tomography (CT) scan of the cervical spine demonstrated the presence of a bony orifice for the left vertebral artery within the transverse process of C7 (Fig 3). This bony canal was believed to cause compression of the left vertebral artery on head turn, with occlusion of flow leading to vertebrobasilar insufficiency in a patient whose contralateral artery already lacked patency. Although it was believed that extreme head turn to the right could also cause the left vertebral artery to undergo compression (thus explaining the patient's newer-onset symptoms on right head turn), this was not observed during the test.Fig 3A computed tomography scan of the cervical spine at the level of C7 demonstrates the presence of an accessory bony canal (arrow) within the transverse foramen.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Given the debilitating nature of the patient's symptoms and the radiographic findings consistent with mechanical compression of the left vertebral artery on head turn, a surgical decompression of the left vertebral artery was performed, and the anterolateral portions of the left C6 and C7 vertebra were removed. The patient tolerated the procedure well, with an uneventful postoperative course, and was discharged on postoperative day 2. A follow-up CT angiography (CTA) 4 months after the procedure demonstrated no evidence of compression or stenosis of the left vertebral artery along its course. The patient reported complete resolution of his vertebral basilar symptoms. A 28-year-old woman presented with a 10-year history of episodes of dizziness, ataxia, and diminished vision occurring on rotation of her head to the right with slight hyperextension. These symptoms would resolve upon reestablishment of normal head position. She also complained of right arm numbness with adduction. Her symptoms were reproduced in the office with rotational changes in position of her head and neck. An angiogram revealed a symmetric vertebrobasilar system with entirely normal vertebral arteries while in neutral head position (Fig 4). However, when the patient's neck was turned to the right, there was evidence of compression to the point of cessation of flow in the right vertebral artery in front of the C7 transverse process (Fig 5). This compression was later noted on CT to be due to a hypertrophic transverse process of the C7 vertebrae (Fig 6). Simultaneously, compression of the contralateral vertebral artery at the C0-C1 interspace was also noted.Fig 5An angiogram of the right vertebral artery in right head turn position shows evidence of flow disruption at the level of C7.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Fig 6A preoperative computed tomography scan of the cervical spine demonstrates a right hypertrophic transverse process of C7 with the right vertebral artery present within the transverse foramen (arrow).View Large Image Figure ViewerDownload Hi-res image Download (PPT) The patient underwent right vertebral artery decompression with removal of the anterior tubercle, costotransverse bar, and posterior tubercle of C7, as well as removal of a large portion of the C6 transverse process. The patient's postoperative course was uncomplicated, and she was discharged on postoperative day 2. Upon follow-up, the patient reported complete resolution of symptoms (Fig 7). Vertebral artery compression is generally asymptomatic; however, if the contralateral vertebral artery is compromised by congenital hypoplasia, atresia, or acquired occlusion or stenosis, vertebrobasilar symptoms may manifest secondary to inadequate perfusion.2Horowitz M. Jovin T. Balzar J. Welch W. Kassam A. Bow Hunter's syndrome in the setting of contralateral vertebral artery stenosis: evaluation and treatment options.Spine. 2002; 27: E495-E498Crossref PubMed Scopus (27) Google Scholar, 3Bauer R.B. Mechanical compression of the vertebral arteries.in: Berguer R. Bauer R.B. Vertebrobasilar arterial occlusive disease: medical and surgical management. Raven Press, New York1984: 45-71Google Scholar, 6Vilela M.D. Goodkin R. Lundin D.A. Newell D.W. Rotational vertebrobasilar ischemia: hemodynamic assessment and surgical treatment.Neurosurgery. 2005; 56: 36-45PubMed Google Scholar, 15Cagnie B. Barbaix E. Vinck E. D'Herde K. Cambier D. Extrinsic risk factors for compromised blood flow in the vertebral artery: anatomical observations of the transverse foramina from C3 to C7.Surg Radiol Anat. 2005; 27: 312-316Crossref PubMed Scopus (35) Google Scholar The symptoms of vertebrobasilar ischemia include dizziness or vertigo, diplopia, nausea, dysarthria, dysphagia, or drop attacks and syncope.2Horowitz M. Jovin T. Balzar J. Welch W. Kassam A. Bow Hunter's syndrome in the setting of contralateral vertebral artery stenosis: evaluation and treatment options.Spine. 2002; 27: E495-E498Crossref PubMed Scopus (27) Google Scholar, 3Bauer R.B. Mechanical compression of the vertebral arteries.in: Berguer R. Bauer R.B. Vertebrobasilar arterial occlusive disease: medical and surgical management. Raven Press, New York1984: 45-71Google Scholar, 4Kuether T.A. Nesbit G.M. Clark W.M. Barnwell S.L. Rotational vertebral artery occlusion: a mechanism of vertebrobasilar insufficiency.Neurosurgery. 1997; 41: 427-433Crossref PubMed Scopus (148) Google Scholar, 7Nagashima C. Vertebral artery insufficiency and cervical spondylosis.in: Fein J.M. Flamm E.S. Cerebrovascular surgery. Springer-Verlag, New York1985: 529-555Crossref Google Scholar, 16Sturzenegger M. Newell D.W. Douville C. Byrd S. Schoonover K. Dynamic transcranial Doppler assessment of positional vertebrobasilar ischemia.Stroke. 1994; 25: 1776-1783Crossref PubMed Scopus (44) Google Scholar This neurologic dysfunction is secondary to ischemia of the brain stem, cerebellum, or occipital lobe, and the symptoms may occur as a single event or as repetitive or progressive events.2Horowitz M. Jovin T. Balzar J. Welch W. Kassam A. Bow Hunter's syndrome in the setting of contralateral vertebral artery stenosis: evaluation and treatment options.Spine. 2002; 27: E495-E498Crossref PubMed Scopus (27) Google Scholar Vertebrobasilar ischemia is generally caused by intrinsic factors, such as atherosclerosis, arterial dissection, or emboli, while extrinsic causes are less common.1Bulsara K.R. Velez D.A. Villavicencio A. Rotational vertebral artery insufficiency resulting from cervical spondylosis: case report and review of the literature.Sug Neurol. 2006; 65: 625-627PubMed Google Scholar, 8Tsutsumi S. Ito M. Yasumoto Y. Simultaneous vertebral artery occlusion in the lower cervical spine manifesting as bow hunter's syndrome.Neurol Med Chir (Tokyo). 2008; 48: 90-94Crossref PubMed Scopus (23) Google Scholar Extrinsic factors causing vertebral compression include osteophyte formation, cervical spondylosis, tendinous bands, or tumors—all of which can cause mechanical compression of the vertebral artery on head rotation—therefore contributing to the etiology of Bow Hunter's syndrome.1Bulsara K.R. Velez D.A. Villavicencio A. Rotational vertebral artery insufficiency resulting from cervical spondylosis: case report and review of the literature.Sug Neurol. 2006; 65: 625-627PubMed Google Scholar, 8Tsutsumi S. Ito M. Yasumoto Y. Simultaneous vertebral artery occlusion in the lower cervical spine manifesting as bow hunter's syndrome.Neurol Med Chir (Tokyo). 2008; 48: 90-94Crossref PubMed Scopus (23) Google Scholar, 10Velat G.J. Reavey-Cantwell J.F. Ulm A.J. Lewis S.B. Intraoperative dynamic angiography to detect resolution of bow hunter's syndrome: technical case report.Surg Neurol. 2006; 66: 420-423Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar, 17Ogino M. Kawamoto T. Asakuno K. Maeda Y. Kim P. Proper management of the rotational vertebral artery occlusion secondary to spondylosis.Clin Neurol Neurosurg. 2001; 103: 250-253Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar, 18Sheehan B.R. Meyer J. Vertebral artery compression in cervical spondylosis.Neurology. 1960; 10: 968Crossref Google Scholar Among the reports discussing mechanical compression of the vertebral artery by osteophytes with head rotation, the C5 and C6 vertebrae were most frequently involved.1Bulsara K.R. Velez D.A. Villavicencio A. Rotational vertebral artery insufficiency resulting from cervical spondylosis: case report and review of the literature.Sug Neurol. 2006; 65: 625-627PubMed Google Scholar, 3Bauer R.B. Mechanical compression of the vertebral arteries.in: Berguer R. Bauer R.B. Vertebrobasilar arterial occlusive disease: medical and surgical management. Raven Press, New York1984: 45-71Google Scholar, 6Vilela M.D. Goodkin R. Lundin D.A. Newell D.W. Rotational vertebrobasilar ischemia: hemodynamic assessment and surgical treatment.Neurosurgery. 2005; 56: 36-45PubMed Google Scholar, 7Nagashima C. Vertebral artery insufficiency and cervical spondylosis.in: Fein J.M. Flamm E.S. Cerebrovascular surgery. Springer-Verlag, New York1985: 529-555Crossref Google Scholar, 16Sturzenegger M. Newell D.W. Douville C. Byrd S. Schoonover K. Dynamic transcranial Doppler assessment of positional vertebrobasilar ischemia.Stroke. 1994; 25: 1776-1783Crossref PubMed Scopus (44) Google Scholar Typically, the uncinate process encroaches on the underlying transverse foramen from an anteromedial direction, forcing the vertebral artery into a posterolateral direction resulting in compression during head rotation.14Bruneau M. Cornelius J.F. Marneffe V. Triffaux M. George B. Anatomical variations of the V2 segment of the vertebral artery.Neurosurgery. 2006; 59 (discussion ONS20-4): ONS20-ONS24Crossref PubMed Scopus (116) Google Scholar Tsutsumi et al8Tsutsumi S. Ito M. Yasumoto Y. Simultaneous vertebral artery occlusion in the lower cervical spine manifesting as bow hunter's syndrome.Neurol Med Chir (Tokyo). 2008; 48: 90-94Crossref PubMed Scopus (23) Google Scholar reported a case in which the patient suffered from both an osseous protrusion into the C5 transverse foramen as well as hypertrophic filamentous tissue. We believe our case of vertebral artery compression within an accessory canal in the C7 transverse foramen is unique. Osteophytes were not the underlying source of obstruction to arterial flow in either patient, and to our knowledge, there have been no publications to date discussing Bow Hunter's syndrome as a result of vertebral artery compression at the level of C7. In both of the cases in this report, patient symptoms were well documented and reproducible in the office as well as during imaging studies. The imaging studies performed included conventional angiography, MRA, and CT, which were highly effective in demonstrating the underlying etiology of the patient's symptoms. Both patients also responded well to decompression procedures, with complete resolution of symptoms. On the basis of our experiences, we recommend that assessment for patients suffering from rotational vertebrobasilar symptoms include magnetic resonance imaging or CT as well as angiography in the neutral and symptomatic positions. In addition, although all vascular interventions carry a risk, the cases we have discussed here highlight the benefit of vertebral decompression procedures in well-selected patients. Postoperatively, patients can expect substantial symptomatic relief and improvement in quality of life.