聴力に異常のないアブミ骨筋腱欠損例

Congenital middle ear anomalies could involve the ossicles, middle ear cleft, and middle ear muscles and tendons. Among these, the absence of a stapedius tendon is a rare middle ear malformation. Herein, we present a case of absent stapedius tendon not associated with hearing impairment. A 24-year-old woman was referred to Kyoto University Hospital with left facial palsy after being prescribed systemic corticosteroid therapy. The hearing level in both ears was below the standard threshold, but the left stapedius muscle reflex was absent. Trans-mastoid decompression of the facial nerve canal was performed because of the low ENoG value. During the surgery, we found a defect in the left pyramidal eminence and an absent stapedius tendon. A review of the preoperative computed tomographic images also revealed a deficiency of the stapedius muscle. Although in most previously reported clinical cases, the absence of a stapedius tendon was accompanied by hearing loss, our patient had a normal hearing level. This case suggests that a defect of the stapedius tendon might not affect the hearing ability. Because subjects with normal hearing would have limited opportunities to have their stapedius tendon examined, the incidence of an absent stapedius tendon in the clinical setting is lower than that in cadaver studies.