In Reply: Three-Dimensional Evaluation and Classification of the Anatomy Variations of Vertebral Artery at the Craniovertebral Junction in 120 Patients of Basilar Invagination and Atlas Occipitalization.

Abstract

To the Editor: We appreciate the comments of Sardhara et al1 regarding our paper entitled “Three-Dimensional Evaluation and Classification of the Anatomy Variations of Vertebral Artery at the Craniovertebral Junction in 120 Patients of Basilar Invagination and Atlas Occipitalization” published in Operative Neurosurgery.2 We regretted not citing the research by Sardhara et al3 in our paper, as there were so many papers concerning the vertebral artery (VA) variations at the craniovertebral junction (CVJ). We could not cite all the information in the literatures. In your study, the anatomical parameters between VA variations and bony deformity were measured and a total score for risk stratification of VA injury during surgery was calculated.3 Your paper had given many useful and beneficial clinical experiences. However, the preventive strategies of different type of VA injury and clinical value of anatomical parameters were majorly discussed in our paper.2 There might be some misunderstanding of the comments of Sardhara et al.1 In our study,2 the traditional three-dimensional (3D) computed tomography angiography (CTA) was used just as most of the literature reported. The limitation of the traditional 3D reconstruction software is that the circumambient osseous of VA cannot be transparent and the special course of VA variations in the osseous deformities cannot be clearly recognized. In our study, the separating, fusing, opacifying and false-coloring-volume rendering technique was used to process the traditional 3D-CTA image. Based on our experiences, it only takes another 5 to 10 min to realize the differentiation of anatomical structures with a different opacity value. Therefore, we concluded that such technique is a convenient and concise method for preoperative evaluation of safety screw placement and for identifying the risk of VA injury in congenital anomalies at the CVJ. In our center, we have treated CVJ anomalies since the 1980s and have accumulated experience of over 3000 cases. We started the VA research very early. As early as 2005, we had reported a kind of VA entering subarachnoid space at the C2 to C3 intervertebral level,4 which is consistent with the abnormal VA as a C3 segmental artery mentioned in the author's letter. With the number of cases increased over the years, we did further study with the biggest cohort. Although the abovementioned kind of VA variations is rare, we found it in 3 patients in our study. The result we reported was still earlier than those reported by Moon et al.5 Patients with basilar invagination and atlas occipitalization usually present abnormal anatomy of the VAs at the CVJ. In managing such complex diseases, spine surgeons are greatly challenged with issues regarding how to intraoperatively address the VA. Failure to recognize them may lead to catastrophic complications. In fact, multiple modalities have been routinely used to detect the aberrant VA, like the 3D imaging reconstruction technique, mixed reality technique and 3D printed technique. With the assist of these techniques, the risks of VA injury would be reduced and the optimal surgical results would be achieved for patients. Funding This study did not receive any funding or financial support. Disclosures The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.