A Case of Congenital Malformation of the Middle Ear with Normal External Ear

A tendonous structure between an abbreviated incus long leg and the pyramidal eminence

Abstract

The patient, a 42-year-old male, who had had nonprogressing hearing impairment of the right ear for about 12 years. Middle ear malformation was diagnosed preoperatively. The pure tone audiogram showed an air-bone gap of 25-40dB. High resolution CT-scanning revealed an abnormal high density shadow at the site of the stapes. Impedance audiometry, the tympanogram was A-type and no stapedial reflex was elicited.
The operative findings were;
(1) The superstructure of the stapes was absent, and the long leg of the incus was abbreviated.
(2) The incudomallear joint was fused osseously.
(3) An abnormal bony mass replaced the stapes.
(4) The oval window was located slightly anteriorly.
(5) A tendonous structure bridged the abbreviated incus long leg and the pyramidal eminence.
The tendonous structure was the most characteristic feature of this case. It has been reported so far only by Isenberg et al. in 1980.
The tendonous structure was considered to be a stapedial tendon, and the reason that no stapedial reflex could be elicited was thought to be the malformation of the stapedial muscle and/or the osseous fusion of the incudomallear joint.