[Two cases of unilateral lesion of the inferior colliculus presenting with temporally changing, distinctive tinnitus and hearing impairment].

We report two cases of unilateral lesion of the inferior colliculus presenting with distinctive tinnitus and hearing impairment. Case 1 was a 40-year-old woman under treatment for multiple sclerosis who developed sudden tinnitus in her bilateral ears, initially resembling a "propeller"-like sound, which evolved into high-pitched "hyun-hyun" tones and subsequently into sustained "hyuun-hyuun" tones. She also exhibited impaired perception of spoken language. Brain MRI revealed a new small lesion in the right inferior colliculus. Case 2 was a 49-year-old man who experienced sudden onset of tinnitus characterized by alternating cicada-like, bell-like, and electronic "pyuun-pyuun" sounds. MRI revealed a small hemorrhage in the right inferior colliculus. In both cases, the characteristics of tinnitus changed over time and was accompanied by impaired recognition of speech sounds. These findings suggest that unilateral inferior colliculus lesions, a relay nucleus of the auditory pathway, can cause temporally evolving tinnitus and selective hearing deficits, symptoms that have been rarely reported.