2.2 Study design and participants
We reviewed retrospectively medical records of all patients treated as SSNHL initially and diagnosed as AN finally after undergoing MRI, who were admitted to our hospital between 2008 and 2021. These patients met the clinical diagnostic criteria for SSNHL, which is defined as sensorineural hearing loss of 20 dB or more over at least 2 contiguous frequencies that develops within 3 days [1]. Data collection included patient demographics, associated complaints (mostly tinnitus and vertigo), results of pure-tone audiometry (PTA), ABR and MRI examination. Exclusion criteria included known previous or progressive hearing loss, AN has been diagnosed before SSNHL occurred and another inner-ear disease. Patients who did not undergo MRI examination were also excluded.