Although the incidence of tegmen tympani dehiscence is relatively high, diagnosis can be difficult if there are no clinical clues or a high degree of suspicion. We describe the case of a 79-year-old male patient with progressive left-sided hearing impairment and ear ringing for 1 year who was eventually diagnosed with middle ear meningocele. Audiometry showed conductive hearing loss with an air-bone gap of 20 dB. This was caused by impaired mobility of the ossicular chain due to meningocele herniation from the dehiscence of the tegmen tympani. In the absence of typical symptoms, such as cerebrospinal fluid middle ear effusion and otorrhoea, diagnosis of tegmen tympani dehiscence may be challenging. Consequently, tegmen tympani dehiscence should be included in the differential diagnosis of conductive hearing loss, which may be the only or early clinical manifestation of tegmen tympani dehiscence. High clinical suspicion and fully assessment are necessary to prevent misdiagnosis and further serious complications. KEY WORDS: Tegmen tympani, dehiscence, meningocele, conductive hearing loss INTRODUCTIONThe tegmen tympani is a thin bony plate that separates the cranial and tympanic cavities. Dehiscence of the tegmen tympani may be accompanied by herniation of the meninges or brain (meningocele or meningoencephalocele). The findings from an autopsy study suggest that 15% to 34% of specimens contain a single defect in the tegmen of the temporal bone

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