# Computerized Tomography Morphometric Assessment of the Internal Acoustic Meatus: Sex Differences, Orientation Angles, and Surgical Implications

## TL;DR

This study uses CT scans to analyze the internal acoustic meatus, finding that its size is similar across sexes and ages, but its orientation angles differ by sex, which could aid in surgery and forensics.

## Contribution

The study introduces the IAM orientation angle as a novel spatial parameter with potential clinical and forensic relevance.

## Key findings

- IAM size parameters show no significant sex- or age-related differences.
- Lateral angle and orientation angle differ significantly by sex, with females showing higher lateral angle values.
- IAM orientation on CT can support surgical planning and provide morphometric information in forensic contexts.

## Abstract

Objective: We aimed to evaluate the morphometric characteristics of the internal acoustic meatus (IAM) using high-resolution computed tomography (CT), with emphasis on sex- and age-related differences, with particular emphasis on the IAM orientation angle as a less-studied spatial parameter and its potential clinical and forensic relevance. Methods: Temporal bone CT scans of 162 patients (94 females, 68 males; age 1–77 years) were retrospectively analyzed. Measurements included the IAM inlet diameter, length, mid-diameter, lateral angle (LA), and orientation angle. Inter-observer agreement was assessed in 30 randomly selected cases. Morphometric parameters were compared by sex and age using t-tests and Mann–Whitney U tests. Results: Mean IAM lengths were 11.0 mm (right) and 11.1 mm (left), and the mean mid-diameter was 4.2 mm bilaterally. IAM lengths and diameters showed no significant sex- or age-related differences (p > 0.05). In contrast, LA and orientation angle differed significantly by sex (p < 0.05), with females showing higher LA values, which may influence posterior fossa surgical exposure. Conclusions: IAM size parameters are largely independent of sex and age, whereas lateral and orientation angles exhibit sex-related variation. Preoperative evaluation of IAM orientation on CT can support skull base surgical planning, and LA may provide supportive morphometric information in forensic contexts, although it should not be considered a standalone sex classification parameter.