From Profiles to Structure in Cochlear Nerve: A Clinical Study of Auditory Neuropathy

Abstract

Objectives: To investigate the clinical and audiological features in auditory neuropathy (AN) patients with different image performance of cochlear nerve (CN) on MRI.

Methods: AN patients were selected from the Multicenter Study on Clinical Diagnosis and Intervention of AN (2003-2023). Subjects were divided into four groups by CN size on MRI: bilateral AN with CN normalization (BAN^cnn), bilateral CN deficiency (BAN^cnd), unilateral AN with CND (UAN^cnd), and CN normalization (UAN^cnn) groups. Clinical and audiological features were analyzed, alongside differential analysis using the Internal auditory meatus (IAM) grading system.

Results: Totally 132 cases were included. The rate of CND was 35.6% (47/132), with 32.7% (36/110) and 50.0% (11/22) in bilateral and unilateral AN patients. The proportion of IAM I to IV grades increased progressively. Clinical and audiological characteristics differed between bilateral and unilateral AN patients. For bilateral AN patients, the age of onset and diagnosis of BAN^cnd were older, which were 11.8 ± 7.2 years and 19.5 ± 11.1 years, respectively, compared to patients in BAN^cnn group. UAN^cnd patients exhibited more severe hearing loss at all frequencies compared to UAN^cnn. Prognostic analysis indicated that AN patients with CND had no lower intervention rates.

Conclusion: The detection rate of CND was 35.6%, predominantly in unilateral AN patients and IAM IV was the most common type. Some clinical and audiological indicators were associated with imaging features of CN but varied between bilateral and unilateral AN. Variation in image performance may not be related to prognosis in AN patients.

Keywords: audiology; auditory neuropathy; cochlear nerve deficiency.

FIGURE 1

Flowchart of screening. (AN: auditory neuropathy, CND: Cochlear nerve deficiency, CNN: Cochlear nerve normalization, BAN^cnn: Bilateral AN patients with CNN; BAN^cnd: bilateral AN patients with bilateral CND; UAN^cnn: unilateral AN patients with CNN; UAN^cnd: unilateral AN patients with CND; IAM: internal auditory meatus nerve grading system; IAM 0–V grades were respectively used to represent no nerves, one nerve, two nerves, three nerves (grades 0–III, CN aplasia), four nerves (grade IV, CN hypoplasia), or normal CN (grade V).).

FIGURE 2

Percentage and images of each IAM grade. (A) The proportion of each IAM grade in patients with bilateral AN; (B) The proportion of each IAM grade in patients with unilateral AN; (C) The internal auditory canal on the axial plane (make a marker at the level of the lateral third in the IAC). (n represent the number of ears; % represent the proportion of each IAM; IAM: Internal auditory meatus nerve grading system; IAM 0‐V grades were respectively used to represent no nerves, one nerve, two nerves, three nerves (grades 0‐III, CN aplasia), four nerves (grade IV, CN hypoplasia), or normal CN (grade V); Others represent CN hypoplasia and absent other nerves.).

FIGURE 3

Audiological characteristics for unilateral AN patients. (A) Pure tone and behavioral audiometry in two groups; (B) ASSR (auditory steady‐state response) in two groups; (C) The proportion of patients with different degrees of hearing loss in two groups; (D) Pure tone and behavioral audiometry in IAM1‐V groups; (E) ASSR in IAM III‐V groups; (F) The proportion of patients with different degrees of hearing loss in IAM I‐V grades. (UAN^cnn: unilateral AN patients with CN normalization; UAN^cnd: Unilateral AN patients with CND; different patterns of connecting lines represent IAM I‐V grades in the line chart; Different colors represent different degree of hearing loss in the column stacking diagram; % represent the proportion of different degree of hearing loss; * represent p < 0.05; n represent the number of ears).