The Normal Adult Human Internal Auditory Canal: A Volumetric Multidetector Computed Tomography Study

Objective: The purpose of this study was to demonstrate that volumetric analysis of multidetector computed tomography (CT) images can be used to calculate the volume of the adult human internal auditory canal (IAC) reproducibly, and to describe the range of normal IAC volumes in the adult population with subgroup analysis of sex, age, and laterality. Background: Previous studies of the IAC have typically used measurements in two dimensions or by using casts of cadavers to measure IAC volumes. This study is the first to report the normal ranges of IAC volumes measured by CT. Methods: Two hundred eighty-one CT scans were assessed. Of the CT scans that met the inclusion criteria, a software package was used to manually contour the IACs in each subject to calculate the volumes in cubic millimeters. Subgroup analysis of laterality, sex, and age was evaluated. Interobserver agreement was calculated for the first 59 patients (118 canals). Results: Two hundred fifty-nine scans (518 canals) met the inclusion criteria. The volumes ranged from 74 to 502 mm3, with no statistically significant difference between left and right (p value = 0.69). In males, the range of volumes measured 74 to 502 mm3 while in females it ranged from 78 to 416 mm3. Males had larger IAC volumes than females (Wilcoxon rank-sum test: S = 14,845.0, p value = 0.01 on the right, and S = 14,646, p value = 0.004 on the left). No correlation was found with age (Spearman: −0.10, p value = 0.09 on the right and −0.04, p value = 0.50 on the left). Excellent interobserver agreement was found. Conclusion: IAC volumes of normal adult subjects, measured by CT, were larger in males and not significantly different with respect to age or laterality.

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