Congenital bony fixation of the malleus

Bony fixation of the malleus seems to be one of the most controversial clinical entities among various congenital disorders of the auditory ossicles. According to various theories, it could be caused by trauma, chronic infection of the ear, otosclerosis or even development failures in the tympanic cavity itself. Histological analysis of 1,108 temporal bones showing a normal middle ear structure was performed. All bones were cut in serial sections of 20 microns. Audiograms and the data on ear trauma or chronic infection were analysed from case histories belonging to each bony specimen. Bony fixation of the malleus was found in 14 cases. It was almost always unilateral. The most frequent site of the fixation was the lateral epitympanal wall. The forms of fixation differed from a thin bony lamella to a solid bony bridge. The mallear ligaments were not involved in any case. No relationship to chronic ear infection, ear trauma or otosclerosis was found. Only a slight conductive hearing impairment up to 20 dB was recorded in 6 out of 14 cases. The most probable predisposing anatomical factors for the onset of the bony fixation of the malleus and the most recent preoperative diagnostic possibilities are discussed.