89. 3D evaluation and classification of the anatomy variations of vertebral artery at the craniovertebral junction

Abstract

BACKGROUND CONTEXT Patients with basilar invagination (BI) and atlas occipitalization usually present abnormal anatomy of the vertebral arteries (VAs) at the craniovertebral junction (CVJ). PURPOSE To describe and further classify different types of VA variations at the CVJ with 3D visualization technology. STUDY DESIGN/SETTING To display the 3D structures of the VA and bone with different colors to summarize different types of VA variations. PATIENT SAMPLE A total of 120 patients with BI and atlas occipitalization who had undergone 3D-CTA were retrospectively studied. OUTCOME MEASURES Abnormal anatomy of the VA at the CVJ was categorized and related anatomic parameters were measured. METHODS Imaging data were processed via the separating, fusing, opacifying and false coloring-volume rendering (SFOF-VR) technique. RESULTS Seven different types were classified. Type I, the VA enters the cranium after leaving the VA groove on the posterior arch of atlas (26.7% of 240 sides). Type II, the VA enters an extraosseous canal created in the assimilated atlas lateral mass-occipital condyle complex before reaching the cranium (53.3%). Type III, the VA course above the axis facet or curves below the atlas lateral mass then enters the cranium (11.7%). Type IV, the VA enters the spinal canal under the axis lamina (1.3%). Type V, high-riding VA (31.3%). Type VI, fenestrated VA (2.9%). Type VII, absent VA (4.2%). Distance from the canal of Type II VA to the posterior facet surface of atlas lateral mass(5.51±2.17mm) means a 3.5 mm screw can be safely inserted usually. Shorter distance from the midline (13.50±4.35) illustrates potential Type III VA injury during exposure. Decreased height and width of axis isthmus in Type V indicate increased VA injury risks. CONCLUSIONS The courses of VA variations in patients with BI and atlas occipitalization were described and classified into seven different types utilizing the SFOF-VR technique, which is highly recommended as a convenient and concise method for the preoperative evaluation. This new classification system and related anatomical parameters allow for improved understanding of the 3D relationship between the course of VA variations and CVJ anatomy, which is important for minimizing the risk of intraoperative VA injury in patients with congenital anomalies at the CVJ. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.