Correlation of cochlear nerve diameter with auditory outcome of cochlear implant surgery



Case Type

Clinical Cases


Dr Madhuri Ghate, Dr Rashmi Kotkar, Dr Sagar Maheshwari & Dr Vigyat Kamal
Krsna Diagnostics PVT LTD; Pawana Nagar Housing Society 411033 Chinchwad, India;


2 months, male


Area of InterestNeuroradiology brain ; Imaging Technique MR
Procedure Education ; Special Focus Seizure disorders ;


To study the anatomy of Internal auditory canal. To assess the diameter of cochlear nerve (CN) in Internal auditory canal (IAC)using heavily weighted T2WI in Oblique parasagittal plane and bony cochlear nerve canal diameter using HRCT temporal bone in patients undergoing cochlear implant (CI) surgery. To assess correlation of diameter of CN with auditory outcome in post-cochlear implant surgery.


Cochlear implant is main treatment of patients with congenital bilateral sensorineural hearing loss. Implant electrode in the device stimulates CN which the sends impulse to the auditory brainstem and is interpreted as sound. Important prerequisite for CI surgery is intact CN. Imaging with HRCT and High-resolution MR helps in assessing the congenital abnormalities associated with the inner ear and CN. It can also help in surgical planning for CI wrt choosing the side of the ear for CI and preoperative counseling of the patients.


Study was performed on 28 patients between age group of 6 months to 3 years who were diagnosed of having bilateral sensorineural hearing loss using HRCT and MRI temporal bone on 128 slice CT scanner and 3T MRI. HRCT scan was acquired using 0.625 mm axial and coronal sections. For CN evaluation, MRI protocol was tailored with oblique parasagittal 3D FIESTA sequences. Long diameter of CN was measured at fundus of IAC using electronic calipers. 3 patients having congenital cochlea abnormalities were excluded from study. Remaining 25 patients were divided into those with CN diameter > 0.5 mm and those with < 0.5 mm.CN was considered deficient when it was smaller than facial nerve and was considered absent when it was not visualized in IAC. Size of bony CN canal was measured on HRCT temporal bone on axial sections. All patients underwent CI before age of 2 years. Preoperative and 2 years postoperative assessment of auditory performance was performed using CAP (categories of auditory performance) score.


We found that the preoperative CN diameter of > 0.5 mm has a positive correlation with good CI outcome (CAP score 3 and more) (p-value < 0.05). In all the patients with CN diameter of < 0.5 mm; diameter of bony CN canal was < 2 mm.


Preoperative assessment of CN diameter can help in predicting auditory outcome in CI patients. It can also help in surgical planning such as the preference of ear for implantation and preoperative counseling.
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