Case study Anatomical variations of vertebral artery and C2 isthmus in atlanto-axial fusion: Consecutive surgical 100 cases Bong Ju Moon a , Kyung Ho Choi b , Dong Ah Shin b , Seong Yi b , Keung Nyun Kim b , Do Heum Yoon b , Yoon Ha b,⇑ a Department of Neurosurgery, Chonnam National University Hospital and Medical School, Republic Gwangju, Republic of Korea b Department of Neurosurgery, Spine and Spinal Cord Research Institute, Yonsei University College of Medicine, Severance Hospital, Republic Seoul, Republic of Korea article info Article history: Received 5 March 2018 Accepted 23 April 2018 Available online xxxx Keywords: Vertebral artery Anomaly High riding Rheumatoid arthritis Atlantoaxial instability Fusion Fixation abstract VA anomalies in extra- and intraosseous regions of the craniovertebral junction (CVJ) is considered very carefully during the posterior screw fixation for the atlantoaxial instability (AAI). This study aims to compare the incidence and variations of VA anomalies, isthmus and pedicle size of C2 in 100 patients with AAI due to congenital skeletal anomaly (CSA) and acquired disease by using three-dimensional CT angiograms (3D CTA) before surgery. The CSA group contained 48 patients and the acquired disease group consisted of 52. In the CSA group, Os odontoideum was the major cause with 43 patients. The causes of acquired disease were RA in 16 patients and OA in 36 patients. Five patients had the anomalous VA in only CSA group; fenestration 2 patients and persistent first intersegmental (PFIS) artery 3 patients. Between CSA and acquired disease groups, no significant differences were found in the isthmus height, internal height, and pedicle width of C2 except the right internal height that is bigger in CSA group. The high-riding VA (isthmus height <4 mm or internal height <2 mm) had no significant difference between CSA group (27.1%) and acquired disease group (34.6%). However, in acquired disease group, patients with rheumatoid arthritis had smaller left internal height (4.21 ± 1.63 vs. 5.51 ± 1.83 mm) and pedicle width (4.11 ± 1.05 vs. 5.05 ± 1.66 mm) of C2 than those of patients with degenerative osteoarthri- tis. Therefore, in the case of atlantoaxial fusion, we should contemplate VA anomaly and the high-riding VA, especially in patients with CSA and RA. Ó 2018 Elsevier Ltd. All rights reserved. 1. Introduction Revelations in surgical technique at the craniovertebral junction (CVJ) with posterior screw fixation [1] has made it the treatment of choice for atlantoaxial instability (AAI) as opposed to standard wiring methods due to rigid mechanical fixation and subsequent higher fusion rates [2–10]. This transarticular screw (TAS) and C1 lateral mass (LM) and C2 pedicle screw (PS) fixation technique have been widely used for AAI as a result of congenital skeletal anomalies (CSA), inflammatory disorders, degenerative changes and trauma, which have led to lower complication rates [7,8,11–13]. Widespread acceptance of this technique showed the possibility of complications when penetrating the C2 isthmus [14–17]. This ultimately led to a study of 1318 patients, where a risk of potential injury to the vertebral artery (VA) was found to be 4.1%, resulting in catastrophic neurological sequelae [18]. Turning a blind eye to these facts and figures may prove disastrous as the course of the vertebral artery in and around C2 varies in disease free populations [14,19,20], those with CSA [14,21,22] and in patients with acquired disease [23,24] at the CVJ. This led to the development of the pedicle screw technique, which was thought to carry less of a risk, however studies show same rates [25]. Previous studies have shown VA anomalies in the extra- and intraosseous regions of C2 closely relating to CSA [21], possibly from embryological origins [22,26–29]. Not only does this study support Yamazaki’s findings via our CSA group, but it also aims to look at the high riding vertebral artery (an intraosseous anom- aly) in those with acquired disease due to inflammatory and degenerative changes which only a few clinical analyses have done [8,23,30]. Although conventional angiography is the imaging gold stan- dard, its invasiveness and potential risks are disadvantages. On top of this, even though this modality is useful for identifying VA https://doi.org/10.1016/j.jocn.2018.04.058 0967-5868/Ó 2018 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Neurosurgery, Spine and Spinal Cord Research Institute, Yonsei University College of Medicine, Severance Hospital, 50 Yonsei-ro Seodaemun-gu, Seoul 03722, Republic of Korea. E-mail address: hayoon@yuhs.ac (Y. Ha). Journal of Clinical Neuroscience xxx (2018) xxx–xxx Contents lists available at ScienceDirect Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn Please cite this article in press as: Moon BJ et al. Anatomical variations of vertebral artery and C2 isthmus in atlanto-axial fusion: Consecutive surgical 100 cases. J Clin Neurosci (2018), https://doi.org/10.1016/j.jocn.2018.04.058