Abstract
Background
The concept that the morphological and the spatial orientation of the labyrinth does not change postnatally is undergoing a worldwide discussion by cochlear implant surgeons. The main objective of this study was to examine the basal turn angulation of the cochlea relative to the midsagittal line to find a possible relationship with the difficulty in implanting the normal cochlea.
Participants and methods
A retroprospective descriptive study was conducted on two equal groups, each consisting of six cochlear implantees. All patients of both groups were having bilateral profound sensorineural hearing loss with normal patent cochlea. The basal turn angle (BTA) of the cochlea relative to the midsagittal plane was measured using the preoperative axial view of the computed tomography (CT) imaging.
Results
A retrospective study was performed on the first group of six cochlea implantees without difficult cochleostomy as noted in the operative notes and correlated with the postoperative BTAs (range = 55-60 degrees) measured later, using patients' preoperative CT images, which were within the normal range. A blind prospective study was performed on the second group of six patients undergoing cochlear implantation in which difficult cochleostomy was faced intraoperatively in one patient (number 2), whose preoperatively measured BTA was 65 degrees (i.e. more obtuse than the normal range), predicting a rotated cochlea with difficult cochleostomy, which was actually faced intraoperatively. BTAs of other five implantees in this group (55, 62, 50, 56, and 57 degrees, respectively) were within the same range as our first group, predicting no difficulty, and this was also found intraoperatively.
Conclusion
Our results were comparable to those of the three pediatric cochlear implantees reported with difficult cochleostomy in whom the BTAs were more obtuse than normal, indicating a rotated cochlea. The possibility of a rotated cochlea should be borne in mind when difficult cochleostomy is encountered. Measuring the BTA of the cochlea relative to the midsagittal plane in all preoperative CT scans is advised to identify cases in which the basal turn of the cochlea may have an unusual orientation. Scala vestibuli insertion or a combined approach technique in case of encountered difficult cochleostomy is highly recommended.