Correlation between the stereostructure of facial recess and the classification of round window membrane visibility

This study investigates the correlation between the dimensions of the facial recess (FR) and the selection of an electrode array insertion approach in cochlear implantation.

Prospective clinical study.

Single-center.

This study included 51 subjects (60 ears), comprising 30 pediatric and 30 adult ears, who underwent cochlear implantation. According to the St. Thoma's Hospital (STH) classification criteria, two parameters were measured: (1) the horizontal distance (d) from the anterior edge of the vertical segment of the facial nerve (FN) to the posterior edge of the chorda tympani nerve (CTN), measured at a point 5 mm inferior to the short process of the incus; and (2) the vertical height (h) from the center of the electrode array insertion hole to the anterior edge of the vertical segment of the FN.

No statistically significant differences in the d and h values were observed between the pediatric and adult cohorts (P > 0.05). Receiver operating characteristic (ROC) curve analysis indicated that a horizontal distance d of less than 1.95 mm between the anterior edge of the vertical segment of the FN and the posterior edge of the CTN predicted limited round window membrane (RWM) visibility, corresponding to Type IIA (50-100% exposure), Type IIB (0-50% exposure), or Type III (no exposure) classifications. In contrast, the vertical height h demonstrated no significant correlation with RWM visibility.

The horizontal distance of the facial recess is a determining factor for RWM exposure classification, whereas the vertical height is not. An exposure likelihood increases significantly when the horizontal distance exceeds 1.95 mm, thereby favoring electrode insertion via the round window approach.