Measurements of the Position Relationship Between the Inferior Margin of the Oval Window and the Endosteum of Basal Cochlear Turn in Histologic and HRCT Study

Abstract

To identify the optimum and safe location histologically for drilling and fenestration on promontory inferior to the oval window in stapedectomy. The value of application of high-resolution computed tomography (HRCT) scanning and multiple-planar reconstruction (MPR) for this purpose is also assessed. By means of histologic sections and HRCT scanning and MPR for coronal image, measurements were conducted on 3 perpendicular planes in temporal bone sections through the anterior, posterior, and midpoint of the inferior margin of the oval window, respectively. The promontory bone inferior to the posterior portion of the oval window is thickest, which has an average thickness of about 1.1 mm. The endosteum of the basal turn here is deepest under the promontory, which has an average height of about 0.2 mm above the plane of footplate, whereas the distance between the inferior margin of the oval window and the endosteum here is no more than 0.3 mm. The coincidence rate of the measurements by HRCT and histology is up to 90.5%. Relatively safe location for bone of the promontory removal should be restricted in the posterior portion inferior to the oval window, and the burr should be lifted laterally while drilling. Preoperative HRCT scanning and MPR for coronal image would offer a valuable reference to estimate the safe area for bone of the promontory removal in stapedectomy.