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.

A retrospective study of congenital osseous anomalies at the craniocervical junction treated by occipitocervical plate-rod systems

“…Various congenital osseous anomalies at the craniocervical junction have been reported [11][12][13][14][15][16][17][18][19][20][21]. In the current study, the congenital lesions include os odontoideum, occipitalization of the atlas, congenital C2-3 fusion, congenital atlantoaxial subluxation, congenital basilar invagination and combined anomalies.…”

“…First, the method cannot be used to treat the dystopic os odontoideum, or os odontoideum associated with other abnormalities affecting the occipitoatlantal articulation because of the possible associated occipitoatlantal instability. Second, the conjunction of occipitalization of the atlas increases the risks for the insertion of lateral mass screws into the atlas due to high incidence of anomalous vertebral artery at the craniocervical junction [21]. Third, the method is contraindicated in os odontoideum associated with a massive defect of the lateral masses of the atlas [25].…”

Clinical and Anatomical Features as well as Pathological Conditions of Surgically Treated Adult Patients with Occipitalization of the Atlas

“…Embryologically, the VA is formed from the longitudinal anastomosis of the intersegmental arteries, which does not occur before the resegmentation stage of the CVJ. 22 Wang et al 13 described four types of anomalous VA in their 36 patients with occipitalization of the atlas. Although their classification is also applicable to our patients, they did not mention the existence of hypoplastic VAs and V2 segment anomalies such as a hypoplastic transverse foramen.…”

Operative nuances to safeguard anomalous vertebral artery without compromising the surgery for congenital atlantoaxial dislocation: untying a tough knot between vessel and bone

“…8,9 However, little is mentioned about the operative techniques to prevent injury to such vessels. In fact, the steps described are those of tamponade with screw tightening once the injury has occurred.…”