Cochlear Rotation and its Relevance to Cochlear Implantation

• Published in: Cochlear implants international 2010-09, Vol.11 (sup2), p.57-63
• Main Authors: Lloyd, Simon KW, Kasbekar, Anand V, Kenway, Bruno, Prevost, Toby, Hockman, Maurice, Beale, Timothy, Graham, John
• Format: Article
• Language: English
• Subjects: ANATOMY; COCHLEA; COCHLEAR IMPLANT; TEMPORAL BONE
• ISSN: 1467-0100; 1754-7628
• DOI: 10.1179/146701010X12726366067815

Objectives: To investigate changes in cochlear orientation with age and discuss the implications of any change with respect to cochlear implantation. Study Design: Cross-sectional study of computerized tomography scans of the temporal bones in patients with no congenital abnormalities. Patients: 159 patients were included in the study making a total of 318 ears. The age range was nine months to eighty five years. Intervention: Axial compututed tomography scans showing the basal turn of the cochlea were identified. The angle of the basal turn of the cochlea was measured by drawing a line through the long axis of the basal turn and measuring its angle with a line drawn through the midsagittal plane. The patients were grouped according to age and a one way analysis of variance was used to identify any statistically significant change in basal turn angulation. Inter- and intra-observer errors were calculated and presented as repeatability co-efficients. The basal turn angles of 3 difficult cases of cochlear implantation were related to the findings. Results: The mean basal turn angle was 54.6° (range 46.8-63.8°; SD 3.5°). There was a statistically significant reduction in the angulation of the basal turn with increasing age (F = 10.1; p = 0.002). The majority of the change occurs between the ages of eleven and fifteen. The inter-observer reliability co-efficient was 4.8. The intra-observer reliability co-efficient was 2.0. The 3 difficult cases all had basal turn angles that were at the upper limit of the normal range. Conclusions: There is a statistically significant reduction in basal turn angulation relative to the midsagittal plane with increasing age. However, care should be taken in interpreting these results in light of the inherent error in the measuring technique although the intra-observer repeatability coefficient was only 2.0. The more obtuse angulation of the basal turn in children may have implications for cochlear implantation.