# Comparative Anatomical and Morphometric Analysis of Eustachian Tube Across Species

## TL;DR

This study compares the structure of the Eustachian tube across species and finds significant differences, which could help understand middle ear diseases.

## Contribution

The study introduces a new anatomical approach and identifies NOX2's role in Eustachian tube inflammation.

## Key findings

- Rodents have shorter Eustachian tubes with cartilage and bubbles, while miniature pigs have longer, conical structures.
- NOX2 levels increased by 38.6% in inflamed mice, contributing to oxidative stress and inflammation.
- Inflammatory factors IL-1β and COX2 increased, causing mucosal thickening and cell infiltration in inflamed Eustachian tubes.

## Abstract

Background/Objectives: The Eustachian tube (ET) is a physiological channel connecting the middle ear with the external atmosphere. The ET plays a role in maintaining the pressure balance of the middle ear, protecting it from pathogen invasion, and cleaning secretions. Eustachian tube dysfunction (ETD) can lead to middle ear diseases in animals. The ET morphological structure are different across species. Therefore, we aim to compare the anatomical and morphological of ET across species. Methods: The combined skull base–nasal approach was used to anatomy ET. Hematoxylin-eosin, luxol fast blue myelin and immunohistochemical Staining were used to observe the morphology of ET. Results: There were significant differences in the size and structure of ET among species: the rodents ET (mouse: 1.152 ± 0.084 mm; rat: 3.738 ± 0.04355 mm) is characterized by cartilage and obvious bubbles; while the miniature pigs ET (32.34 ± 2.157 mm) has a chondroid conical structure similar to that of humans. ET inflammation model was built by intro-tympanic injection of lipopolysaccharide (LPS). NADPH oxidase 2 (NOX2) significantly increased by 38.6% in inflamed mice, causing ET oxidative stress. The expressions of inflammatory factors interleukin-1β (IL-1β) and cyclooxygenase-2 (COX2) increased by 28.4% and 30.8%, resulting in thickening of the ET mucosa and infiltration of inflammatory cells. Conclusions: The combined skull base–nasal approach was an effective method to anatomy ET across species. The morphology of ET varied across species and NOX2 might play an important role in ET inflammation.