[Inverted axis scans in the study of the lumbo-sacral passage with computed tomography]

In the CT study of the lumbosacral spine, the disk spaces must be scanned along a plane which parallels the relative intervertebral disk perfectly. However, the lumbosacral space often happens to be too oblique--i.e., over the possible inclination of the gantry (usually: +/- 25 degrees). Thus, the somatic planes of the spine overlap. Therefore, in a series of 1,800 patients, the lumbosacral space was studied with the gantry inclined in the opposite direction to that in conventional scans, with the maximum angle allowed by our unit (-25 degrees). The incidence of negative findings for disk conditions was 7% (versus 13.5% with conventional CT). In both the negative and the positive cases, inversion CT scans were diagnostic in 594 patients (468 with disk herniation)--i.e., in 33% of cases.