Rotational changes in the morphology of the vertebral artery at a common site of artery dissection

Objective. Given that vertebral artery dissection and transient vertebrobas ilar insufficiency occurs commonly at the C1-C2 junction, the objective was to study, in vivo, the normal rotational anatomy at C1-C2 using magnetic r esonance angiography (MRA) with 3-dimensional (3D) reconstructions and to c orrelate these reconstructions with our experience of dissection location. Methods: 3D phase-contrast MRAs were obtained from the foramen magnum to C3 in 4 normal volunteers in neutral and rotated (45 degrees) positions. The magnitude images were used as source images for 3D reconstruction. The imag es from only 1 of the volunteers were completely motion free, and these wer e subjected to arterial length calculations using image analysis wire frame outline of the vessel. All angiograms of vertebral artery dissection obtai ned at our institution from 1993 to 1997 were also reviewed. Results: 3D re constructions document elongation (approximately 7% in quantitatively analy zed case) and slight narrowing of the artery contralateral to the direction of head rotation from C2 to the dural entry point. The artery turns most s harply and is subject to the anterior force of the rotating C1 vertebra as it exits the C1 foramen. Of 14 cases of vertebral artery dissection, 50% oc curred between the transverse foramen and the posterior lamina of C1. Concl usions: With head rotation, the contralateral vertebral artery undergoes th e greatest anatomical distortion as it exits the C1 transverse foramen. Thi s increased stress may account for the higher frequency of dissections at t his location.