Method to estimate the basal turn length in inner ear malformation types

Abstract

The mathematical equations to estimate cochlear duct length (CDL) using cochlear parameters such as basal turn diameter (A-value) and width (B-value) are currently applied for cochleae with two and a half turns of normal development. Most of the inner ear malformation (IEM) types have either less than two and a half cochlear turns or have a cystic apex, making the current available CDL equations unsuitable for cochleae with abnormal anatomies. Therefore, this study aimed to estimate the basal turn length (BTL) from the cochlear parameters of different anatomical types, including normal anatomy; enlarged vestibular aqueduct; incomplete partition types I, II, and III; and cochlear hypoplasia. The lateral wall was manually tracked for 360° of the angular depth, along with the A and B values in the oblique coronal view for all anatomical types. A strong positive linear correlation was observed between BTL and the A- (r2 = 0.74) and B-values (r2 = 0.84). The multiple linear regression model to predict the BTL from the A-and B-values resulted in the following equation (estimated BTL = [A × 1.04] + [B × 1.89] − 0.92). The manually measured and estimated BTL differed by 1.12%. The proposed equation could be beneficial in adequately selecting an electrode that covers the basal turn in deformed cochleae.

Applications of visualizing cochlear basal turn in cochlear implantation

“…Oblique coronal view of the cochlear basal turn is also important in visualizing the extent of ossification in the ST due to meningitis infection that enters the cochlea mainly through the cochlear aqueduct. Most of the congenital inner ear malformation types have some degrees of cystic portion of the cochlea which can be seen clearly from the oblique coronal view of the cochlear basal turn 10 . Identifying the cystic portion helps in choosing an optimal length electrode that would prevent placing the electrode into cystic apical portion.…”

“…Most of the congenital inner ear malformation types have some degrees of cystic portion of the cochlea which can be seen clearly from the oblique coronal view of the cochlear basal turn. 10 Identifying the cystic portion helps in choosing an optimal length electrode that would prevent placing the electrode into cystic apical portion. For achieving all the above‐mentioned goals demand for a method with which the optimal oblique coronal view of the cochlear basal turn could be visualized.…”