A vertebral artery without atlantic and intradural sections: a case report and a review of the literature.

Summary This report covers a case in which the right vertebral artery (VA) did not participate in the formation of the basilar artery. The artery had an external diameter of about 1 mm. It ran trough the transverse foramina of C6 through C2, then turned backward and entered the spinal canal and the dural envelope between the posterior arch of C1 and the lamina of C2 as a medullary artery to end in the spinal arteries. The basilar artery was a continuation of the left VA only. Only very few cases of non-union of the VA with the basilar artery have been previously described. Cases with extreme reduction of one of the VAs are not exceptional. This variant is clinically important. On arteriography, this extremely rare condition could easily be misdiagnosed as an obstruction. In view of manipulative therapy and in the detection of vertebrobasilar insufficiency, one has to bear in mind that cases of non-union may influence the interpretation of these tests.