# Tomographic comparison of the cochlea, oval window, round window and facial nerve between adults and children and their influence on cochlear implant surgery

## TL;DR

This study compares the anatomy of the cochlea and facial nerve in children and adults to explain why cochlear implant surgery is more challenging in children.

## Contribution

The study introduces two tomographic measurements to predict round window visibility during cochlear implant surgery.

## Key findings

- The RWM-FN-CP angle is more acute in children compared to adults.
- The RWM-CP vertical distance is smaller in children than in adults.
- These anatomical differences explain the lower visibility of the round window in children during surgery.

## Abstract

•Cochlear implant surgery via round window ensures less trauma.•Understanding morphology and anatomical relationships of the round window is important.•Angle between Round Window Membrane (RWM) and the Facial Nerve (FN) with the Coronal Plane (CP).•Vertical distance between Round Window Membrane (RWM) and the Facial Nerve (RWM-FN).•RWM-FN-CP angle is more acute, and the vertical distance (RWM-FN) is smaller in children.

Cochlear implant surgery via round window ensures less trauma.

Understanding morphology and anatomical relationships of the round window is important.

Angle between Round Window Membrane (RWM) and the Facial Nerve (FN) with the Coronal Plane (CP).

Vertical distance between Round Window Membrane (RWM) and the Facial Nerve (RWM-FN).

RWM-FN-CP angle is more acute, and the vertical distance (RWM-FN) is smaller in children.

Is to compare two tomographic measurements that can be used to predict the visibility of the round window: the angle formed by the junction of the line that goes from the round window Membrane Center Point (MJR) to the Facial Nerve surface (FN) with the Coronal Plane (CP) traced over this surface (RWM-FN-CP Angle) and the vertical distance between the midpoint of the RWM and this Coronal Plane (RWM-CP Vertical Distance); in adults and children, in order to verify if there are significant differences between the groups, which would justify the greater surgical difficulty caused by the lower visibility of the RW in children.

In this retrospective study, the RWM-FN-CP angle and the RWM-CP vertical distance were measured in Computerized Tomography Scans (CT) of patients who underwent CI surgeries.

32 individuals who underwent CT in the period 2015–2018, 16 adults aged 27–73 years, and 16 children, with a mean age of 3.4 (±2.7) years were evaluated. The mean of the RWM-FN-CP angle in children was significantly lower, than the mean in adults. The mean RWM-CP vertical distance in children was significantly lower than the mean in adults (p = 0.0001).

In children, the RWM-FN-CP angle is more acute, and the measured MJR-PC vertical distance is smaller when compared to adults. The anatomical differences observed in the tomographies justify the lower visibility of the RW during the surgical act of cochlear implantation in children.

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