title: Anomalous vertebral artery in craniovertebral junction with occipitalization of the atlas.
abstract: STUDY DESIGN.: Observational study with 3-dimensional computed tomography angiography analysis. OBJECTIVE.: To examine the course of the vertebral artery (VA) at the craniovertebral junction (CVJ) in individuals with occipitalization of the atlas. SUMMARY OF BACKGROUND DATA.: The anatomy of the VA at the CVJ should be completely understood to decrease the risk of iatrogenic injury. Although quantitative anatomic studies have focused on the normal VA, the anomalous VA with occipitalization of the atlas has not been fully explored. METHODS.: A consecutive series of 36 cases with occipitalization of the atlas underwent 3-dimensional computed tomography angiography. Seventy-two vertebral arteries were analyzed. In this setting, the safety of placing lateral mass screws (LMS) was studied. RESULTS.: Four different pathways of the VA at the CVJ with occipitalization of the atlas were found. Type I, wherein the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is below the occipitalized C1 lateral mass (8.3% of 72 vertebral arteries); Type II, the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is on the posterior surface of the occipitalized C1 lateral mass, or makes a curve on it (25%); Type III, wherein the VA ascends externally laterally after leaving the axis transverse foramen, enters an osseous foramen created between the atlas and occipital bone, then into the cranium (61.1%); and Type IV, in which the VA is absent (5.6%). CONCLUSION.: Four types of VA with occipitalization of the atlas are confirmed. Type-I and type-IV VA have relatively low risks for C1 LMS perforation. Type-II and type-III anomalies will probably increase the risk of VA injury during C1 LMS placement. Definite caution should also be taken during the procedure on the contralateral side of a type-IV VA.
authors.affiliation: Departments of Orthopaedic, Peking University Third Hospital, Beijing, China.
authors.forename: Shenglin
authors.initials: S
authors.lastname: Wang
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
authors.forename: Ming
authors.initials: M
authors.lastname: Yan
authors.forename: Haitao
authors.initials: H
authors.lastname: Zhou
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001269:Atlanto-Occipital Joint / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D001270:Cervical Atlas / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008875:Middle Aged; D009777:Occipital Bone / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D011859:Radiography; D013123:Spinal Fusion / Q000379:methods; D014711:Vertebral Artery / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery