The Anatomic Study of Intracranial Structures Related to Clival Screw Placement

A clival plate and screw fitted to the craniovertebral junction (CVJ) were developed in our previous studies. However, the anatomy of intracranial structures related to clival screw placement has not been studied.

To measure the intracranial anatomic parameters delineating the basilar plexus and vertebrobasilar artery (VBA) course and to determine the relationship between brainstem and clivus for safer screw placement.

Morphometric analysis of the VBA was conducted on 95 patients (48 men, 47 women) by CT angiography (CTA) and of the basilar plexus and brainstem on 80 patients (44 men, 36 women) by magnetic resonance imaging (MRI) The narrowest distance between the VBA and the intracranial clivus and the distance between the VBA and the median line of the skull were measured on the axial plane at different parts. The relative positions of point I (intersection of vertebral artery and basilar artery) and the pharyngeal tubercle were analyzed. The distance between the clivus and the brainstem was measured at different levels.

As the VBA ascended the distances to the intracranial clivus and the midline decreased. In 83.3% cases, point I was above the pharyngeal tubercle, and in only 9.5% cases was it located on the vertical line drawn from pharyngeal tubercle. The smallest safe space between the intracranial clivus and the brainstem was 7.46 mm at the lower part.

Appropriate screw size at the lower clivus and the pharyngeal tubercle may help avoiding inadvertent injury to the brainstem and the VBA. Preoperative CTA and MRI of the CVJ are suggested to guide the surgeon in this regard.