Magnetic resonance imaging of C2 segmental type of vertebral artery.

Two cases with C2 segmental type of vertebral artery (VA) were reported. One case was a 64-year-old man, who was referred to our hospital suffering from vertigo, ataxia, and right facial palsy. Computed tomography (CT) scan showed multiple lacunae in the basal ganglia bilaterally. Another case was a 47-year-old man, complaining of left hemiparesthesia. A small high density area with a little enhancement was seen in the right parietal region in CT scan, and the lesion was diagnosed as cavernous angioma. Angiography of both cases depicted the vertebral artery not passing through the transverse foramen of the Atlas, but running medioposterior to it, and magnetic resonance imaging (MRI) and CT findings showed the vertebral artery running between the Atlas and Axis, and entering into the spinal canal. In our experience of 1669 sides in 1436 cases, such anomaly of the vertebral artery was found in ten cases including the two abovementioned. Six cases of such anomaly have previously been reported, but demonstration of the VA coursing between Atlas and Axis by MRI has not been published in the literature. During surgical therapy on the upper cervical spine, especially when using a posterior approach, or C1-C2 lateral puncture, the possibility of an anomalous vertebral artery, as in our cases, should be taken into consideration.