Location of the AICA influences the severity but not occurrence of ISSNHL: A reappraisal using high-resolution 3 T MRI

OBJECTIVE: To investigate the potential influence of anatomical variation in the anterior inferior cerebellar artery (AICA) on the occurrence and severity of idiopathic sudden sensorineural hearing loss (ISSNHL). METHODS: Ninety ISSNHL patients were enrolled. The anatomical location of the AICA was exhibited using high-resolution magnetic resonance imaging (MRI), and the various AICA types classified by previously reported Chavda and Gorrie methods were analyzed. The severity of hearing loss in the ipsilateral ear among different AICA types was compared. RESULTS: Approximately 85.6% of subjects had unilateral ISSNHL (uISSNHL), and the others had bilateral ISSNHL (bISSNHL). In the uISSNHL group, the ratios of different AICA types were similar between the ipsilateral and contralateral ears. The ratios of the different AICA types in the bISSNHL group were similar to those in the uISSNHL group. In the uISSNHL group, pure tone audiometry (PTA) thresholds at 2 kHz, 4 kHz and 8 kHz of patients with Chavda type II AICA were higher than those of patients with Chavda type I and type III, with a significant difference at 4 kHz between type I and type II. There was a tendency of the PTA threshold in patients with Chavda type II or Gorrie type C to gradually increase from low to high frequency zones. CONCLUSION: When the AICA enters the IAC (Chavda type II) or crosses between the 7th and 8th cranial nerves (Gorrie type C), the severity and frequency of hearing impairment in ISSNHL but not the occurrence of ISSNHL will be affected.