The internal auditory canal (IAC), which is a nerve canal surrounded by bone, rises anterolaterally from the CPA to reach the peripheral cochleovestibular organs. It contains several crucial structures such as cranial nerves V to VIII, and arteries such as superior cerebellar artery (SCA) and anterior inferior cerebellar artery (AICA). The cerebellopontine angle (CPA) is triangular-shaped space filled with cerebrospinal fluid, and is located at the junction of the pons and cerebellum. In contrast, comparisons of hearing improvement based on Chavda type classification showed a statistical difference, with a higher proportion of Chavda type 1 showing improvements in hearing (AICA outside IAC). Anatomical variances of the AICA loop position did not affect the incidence of ISSNHL or co-morbid symptoms including tinnitus and vertigo. At two frequencies, 1 and 4 kHz, there were differences in Chavda types between hearing improvement and no improvement ( p < 0.05). There were differences in quantitative hearing improvement between AICA types, although without statistic significance ( p = 0.09–0.13). Patients who had combined symptoms such as tinnitus and vertigo did not show a different AICA distribution compared with patients who did not. There was no difference in AICA types between ears with and without ISSNHL. We compared the affected and unaffected ears, and investigated whether there were any differences in hearing recovery and symptoms between the two classification types. Pure tone threshold at four different frequencies (0.5, 1, 4, and 8 kHz), at two different time points (at initial presentation and three months after treatment), were analyzed. Two established classification methods designed by Cahvada and Gorrie et al. We retrospectively reviewed patient data from January 2015 to March 2018.

We adopted two methods to classify the anatomic position of the AICA, then analyzed whether these classifications affected the clinical features and prognosis of ISSNHL. As such, the position of the AICA within the CPA and IAC may be related to the clinical development of ISSNHL. A possible etiology of idiopathic sudden sensorineural hearing loss (ISSNHL) is ischemia of the labyrinthine artery, which is a branch of the AICA. The anatomical shape and location of the AICA is variable within the CPA and internal auditory canal (IAC). It contains cranial nerves and the anterior inferior cerebellar artery (AICA). The cerebellopontine angle (CPA) is a triangular-shaped space that lies at the junction of the pons and cerebellum.

Internal auditory canal mri anatomy