High resolution computed tomography analysis of the temporal bone.

Detailed radiological assessment by high resolution computed tomography (HRCT) of temporal bone is demanded before any temporal bone or skull base surgery. The aim of this study was to measure the relations between the anatomical landmarks of the temporal bone and to assist the otolaryngologist in establishing accurate preoperative evaluation. We enrolled 43 patients who underwent temporal bone HRCT between February 2004 and May 2004. Contiguous axial and coronal images at 1.0 mm thickness were obtained. Some landmarks such as the superior and inferior lips of the internal acoustic canal (IAC), the malleoincus joint, and the posterior semicircular canal were labeled in the coronal and axial views. Then we measured the distance between them. Average IAC diameter in the coronal and axial views was 5.33 mm and 6.92 mm. Average IAC length in the coronal and axial views was 12.29 mm and 11.09 mm. The thickness of the retrolabyrinthine bone was 3.78 mm. The incidence of thinning bone overlying the superior semicircular canal was 2.3%. Our data could be applied to normal distribution because there were no statistical differences between the measurements of normal ears and diseased ears. Several specific measurements can be applied to the preoperative evaluation of vestibular schwannoma including the retrosigmoid approach, the translabyrinthine approach and the middle fossa approach.