title: Magnetic resonance angiographic analysis of atlanto-axial rotation: anatomic bases of compression of the vertebral arteries.
abstract: The aim of this study was to identify the functional anatomic factors involved in the maintenance or disturbance of flow in the vertebral aa. during atlanto-axial rotation. Fourteen healthy volunteers were studied by magnetic resonance angiography (MRA) by a three-dimensional sequence in phase contrast centered on the vertebral aa. at the level of the cranio-cervical junction before and after left rotation of the head. A decrease in the signal intensity of the arterial flow was sought for. The results were compared to the posterolateral development of the loop of the vertebral a. in its atlanto-axial segment in neutral position, and to the measurement of the angular opening between the atlas and axis in dynamic position. Seven subjects also had a three-dimensional CT study (3D CT) of the bony relations of C1 and C2 after rotation. In 4 subjects a disturbance of flow in the right vertebral a. was observed in the transverse foramen of C2. This occurred when two factors were combined: an under-developed atlanto-axial arterial loop and a C1-C2 angle exceeding 35 degrees in maximal rotation. In the other subjects a well-developed arterial loop and/or a C1-C2 angle of less than 35 degrees in maximal rotation were factors preserving the arterial flow. The risk factor associated with the C1-C2 angle seemed correlated in 3D CT with loss of the usual asymmetric character of rotation. A clinical application is reported with a case combining chronic rotational dysfunction of the cranio-cervical junction as shown by 3D CT and complete compression of the vertebral a. in MRA, confirmed by conventional angiography. A knowledge of this physiopathologic mechanism allows clinical detection and evaluation of the risk of any effect of pathology of the cranio-cervical junction on the vertebral a.
authors.affiliation: Institut d'Anatomie Clinique, UFR de Bobigny, Université de Paris Nord, France.
authors.forename: J L
authors.initials: JL
authors.lastname: Dumas
authors.forename: J
authors.initials: J
authors.lastname: Salama
authors.forename: P
authors.initials: P
authors.lastname: Dreyfus
authors.forename: P
authors.initials: P
authors.lastname: Thoreux
authors.forename: D
authors.initials: D
authors.lastname: Goldlust
authors.forename: J P
authors.initials: JP
authors.lastname: Chevrel
mesh_terms: D000293:Adolescent; D000328:Adult; D001268:Atlanto-Axial Joint / Q000502:physiology*; D005260:Female; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D012399:Rotation; D014711:Vertebral Artery / Q000033:anatomy & histology*