Rotational vertebral artery occlusion ("bow hunter syndrome").

PURPOSE: To review the literature, analyze and discuss diagnostic and treatment options for the Bowhunter Syndrome. A clinical case of idiopathic rotatory C1-C2 subluxation causing dynamic vertebral artery occlusion is presented. METHODS: Literature review between 1960 and 2019, discussion of diagnostic methods and treatment options. Description of diagnostic and treatment methods in the aforementioned case. RESULTS: We present a patient with dynamic left vertebral artery occlusion associated with idiopathic rotatory C1-C2 subluxation. A dynamic Angio-CT showed rotatory C1-C2 subluxation with significant flow reduction at the left vertebral artery at the exit of the C2 transverse foramen until the V3 segment when the head rotated towards the right. Due to clinical and radiological worsening in the following months, posterior C1-C2 arthrodesis was performed, with the disappearance of the symptoms. There are 193 cases reported with dynamic vertebral artery occlusion, but in only two, the etiology was primary rotational atlantoaxial instability. The most prevalent etiology was degenerative. CONCLUSION: Rotatory vertebral artery occlusion is a rare condition presented mostly in adults, aged 50-70 years. Vertebrobasilar insufficiency is triggered by the rotation of the head to the contralateral side of the dominant vertebral artery. Dynamic subtraction angiography is considered the diagnostic gold-standard method, but dynamic Angio-CT scan, Angio-MRI, or Doppler ultrasonography are less invasive options. The treatment options are conservative or surgical. Endovascular surgery is another option in specific cases.

Harms C1-C2 instrumentation technique: anatomo-surgical guide.

STUDY DESIGN: Anatomic study. OBJECTIVE: To measure C1 and C2 critical areas related to the screws trajectory, according to Harms technique, in Latin specimens. To investigate vertebral's artery course in cadavers. SUMMARY OF BACKGROUND DATA: To our knowledge there are no studies addressing vertebral surface measurements for screw placement, according to Harms C1-C2 instrumentation technique, nor cadaveric measurements of the trajectory of the vertebral artery in Latin specimens. METHODS: C1 and C2 specimens were measured. C1 measurements: height, width, anteroposterior diameter (intraosseus screw length) and convergence in the axial plane of the lateral mass; length from the posterior border of the posterior C1 arch to the anterior cortex of the articular mass (total screw length). C2 measurements: width, height, convergence and sagittal inclination of the pars interarticularis. Direction of the trajectory of the vertebral artery in the suboccipital region in fresh cadavers. RESULTS: C1: left mass width 14.20 mm, right: 14.32 mm; left intraosseus screw length: 17.17 mm, right 16.9 mm; left total length of the screw: 27.14 mm, right: 26.72 mm; left mass height: 10.22 mm, right: 10.29 mm. Right mass convergence: 24.68°, left: 22.44°. C2: width: left 8.75 mm, right: 8.53 mm; height: left 10 mm, right 9.81 mm; convergence: left 42.15°, right: 38.98°; sagittal inclination: left 35.50°, right 33.07°. Vertebral artery's medial border is between 13 and 22 mm from the middle line of C1 posterior arch. CONCLUSION: Convergence and inclination of the pars are slightly greater than the suggested by Harms. Individual and/or racial variations must be considered. There is enough space for safe placement of a 3.5 mm screw in the lateral masses of C1 and through the pars of C2. Dissecting the superior face of the posterior arch of C1 laterally more than 10 mm from the posterior tubercule could injure the vertebral artery.