Introduction: Cochlear hypoplasia is classified into 4 types. Although types I & II can be easily identified by visual inspection of CT, type II & IV can be easily mistaken as normal cochlear or IP II resulting in surgical difficulties postoperatively. So, we suggest simple indicators for cochlear hypoplasia based on the commonly prevailing axial & coronal CT scans.
Methods: We conducted a retrospective descriptive study on 65 Egyptian children aged 2-14 years old who were candidates for cochlear implantation and showing normal radiologic cochlear anatomy during the peroid 2019 to 2022 in Tanya university hospital. All had full insertion of flex 28 MED-EL electrodes intra-operatively. The preoperative CT scans were reviewed retrospectively to calculate the normative CT measurements of the basal turn length in the axial view, the cochlear height in axial & coronal views and the upper turns height (apical & middle) in the axial view. The mean of these calculations was used & SD was calculated. The cut-off value to suspect cochlear hypoplasia was defined as less than 2 SDs below the calculated mean.
Results: The calculated cutoff value of the axial basal turn length for CH was: 7,5 mm. The calculated cutoff value of the cochlear height in axial view for CH was: 3.1 mm. The calculated cutoff value of the cochlear height in the coronal views for CH was: 4.2 mm. The calculated cutoff value of the upper turns height for CH was: 2.1 mm
Conclusions: We suggest modifying Sennaroglu classification of cochlear hypoplasia by terming the most severe forms (CH I & CH II) as cochlear hypoplasia proper terming the least severe forms (CH III & CH IV) as stunted or miniature cochlea. Stunted cochlea (CH III & IV) may be overlooked by visual inspection alone and cochlear measurements are helpful to differentiate it from normal cochlea or IP II. CH IV is the most difficult to separate from IP II as basal turn length may be normal but upper turns & cochlear heights are diagnostic. In doubtful cases, 3D volume rendering or curved CT may be ordered. These objective CT measurements serves as a guide for electrode selection and planning the surgical approach.
