Use of reconstructed, non-orthogonal plane, high-resolution computed tomography of the temporal bone in the planning of temporal bone surgery

Objectives: To demonstrate the utility of high-resolution computed tomography (HRCT) reconstructed in nonorthogonal planes in the planning of temporal bone surgery. Study Design: Qualitative and quantitative comparison of in vivo anatomic measurements between orthogonal and non-orthogonal plane reformatted HRCT of the temporal bone. Methods: HRCT data of 10 normal temporal bones were reconstructed two-dimensionally in two non-orthogonal planes. Parallel to the plane defined by the superior semicircular canal (defined as transverse) as well as perpendicular to the plane defined by the superior semicircular canal (defined as longitudinal). This was done using commercially available software. Sixteen surgically important relationships between neural, vascular and/or bony structures were measured and analyzed. Results: Quantitatively, wide variations were obtained in the measurements obtained from images of both non-orthogonal planar orientations. These variations were not age or sex dependent. Qualitatively, the images obtained highlight the anatomy of the temporal bone and skull base as it will be encountered during otologic surgery, since the surgical visual axis is along the long axis of the temporal bone. Conclusions: The reformatted images in non-orthogonal planes were superior to the axial and coronal series because they condensed critical relationships into a single perspective which promoted an intuitive understanding of the surgical approach. These reconstructed images show wide differences in quantitative measurements between surgically relevant landmarks. The protocol can be easily implemented in the clinical setting and is a potentially valuable educational tool. We recommend that nonorthogonal reconstructed images be routinely included with orthogonal temporal bone HRCT scans.