Absent stapedius muscle and its tendon concomitant with otosclerosis: a case report on embryology, imaging, and treatment.

This study aimed to discuss the clinical implications associated with the absence of the stapedius muscle and concomitant otosclerosis. The causes of mixed hearing loss are presented based on its embryonic development, audiological tests, and high-resolution computed tomography (CT) imaging. This case describes a 35-year-old female patient diagnosed due to bilateral conductive hearing loss. The patient complained of a significant deterioration of hearing and speech understanding lasting for several months. Preoperative audiometric work-up revealed air-bone gap with the presence of Carhart's notch characteristic for otosclerosis. In CT scans otospongiotic focus was confirmed and the absence of stapedius muscle, its tendon, and pyramidal eminence was discovered. The patient underwent stapedotomy with good hearing result after healing. Understanding the stapedius muscle's development process is essential to comprehend the reason for its failure - the absence of the stapedius muscle results in exposure to acoustic trauma. Patients may experience hypersensitivity to sound, although it was not discovered in the described patient. High-resolution CT is a handy tool for analyzing congenital malformations of the middle ear. The absence of the stapedius muscle may also be indicated by other anatomical variations of the middle ear detected with high-resolution computed tomography images. The absence of the stapedius muscle may coexist with otosclerosis. Detailed in-depth analysis of high-resolution computed tomography images is the only tool to assess for stapes muscle defects without surgical intervention.