Utility of three-dimensional computed tomographic angiography for assessment of relationships between the vertebrobasilar system and the cranial base.

Abstract

The optimal surgical exposure for basilar tip aneurysms is dictated by the relationship of the basilar bifurcation to the cranial base. This study was designed to evaluate three-dimensional computed tomographic angiography as a means of obtaining detailed anatomic information on the basilar artery and the surrounding cranial base in individual patients before surgery. We studied 30 patients using three-dimensional computed tomographic angiographic reconstructions from 1-mm computed tomographic slices. Detailed anatomic measurements were performed to define the relationship between the basilar artery and the cranial base. Particular attention was paid to the height of the dorsum sellae and its relationship to the basilar bifurcation. The heights of the basilar apex and the vertebrobasilar junction, relative to the cranial base, were extremely variable. Considerable asymmetries in the heights of the left and right posterior clinoid processes were identified; in one case, this difference was more than 1 cm (mean difference in height, 0.9 mm; range, 0-10.3 mm). The heights of the posterior clinoid processes above the sellar floor ranged from 5.8 to 14.1 mm (mean height, 9.5 mm). We were able to determine the feasibility of the pterional/orbitozygomatic, middle fossa/ anterior petrosal, and presigmoid retrolabyrinthine approaches to an individual basilar bifurcation. We also estimated the amount of bone removal required and determined the operative distances via those approaches. Three-dimensional computed tomographic angiography is a useful tool for assessing critical anatomic relationships and represents an adjunct to conventional angiography in the planning of individualized, precisely tailored, cranial base approaches to the vertebrobasilar system.