Congenital stapes anomalies with normal eardrum

Abstract

Objectives: A non-progressive and conductive hearing loss with normal eardrum, but no history of trauma and infection, is highly suggestive of a congenital ossicular malformation. Among ossicular anomalies, stapes anomaly is the most common. The purpose of this study is to describe patterns of stapes anomaly and to analyze its surgical outcome with special reference to its patterns.

Methods: We conducted a retrospective case review. The subjects comprised 66 patients (76 ears) who were decisively confirmed by the exploratory tympanotomy as congenital stapes anomalies without any anomalies of the tympanic membrane and external auditory canal. The preoperative and postoperative audiological findings, temporal bone computed tomography scan, and operative findings were analyzed.

Results: There were 16 anomalous patterns of stapes among which footplate fixation was the most common anomaly. These 16 patterns were classified into 4 types according to the status of stapes footplate. Successful hearing gain was achieved in 51 out of 76 ears (67.1%) after surgical treatment.

Conclusion: Footplate fixation was usually bilateral, whereas stapes anomalies associated with other ossicular anomaly were usually unilateral. The success of the surgical treatment of stapes anomaly might depend on its developmental status of the footplate. Stapes anomalies were detected without any fixed patterns, therefore, it is quite possible to detect a large variety of patterns in future.

Keywords: Conductive hearing loss; Ossicular replacement; Stapes.

Fig. 1

Stapes without anterior crus. (A) Schematic presentation. (B) Operative finding shows no anterior crus of the stapes (arrow). c: chorda tympani.

Fig. 2

Stapes without anterior crus and incus long process. (A) Schematic presentation. (B) Removed incus shows no long process, and removed stapes shows no anterior crus.

Fig. 3

Stapes without anterior crus and incus long process with fibrous band. (A) Schematic presentation. (B) Operative finding shows a fibrous band (arrow) instead of the incus long process and the stapes lacking anterior crus (asterisk).

Fig. 4

Stapes without superstructure and incus long process. (A) Schematic presentation. (B) Operative finding shows no incus long process and no stapes superstructure. c: chorda tympani; f: footplate.

Fig. 5

Stapes footplate fixation. (A) Schematic presentation. (B) Operative finding shows half of the stapes footplate remaining (arrow) because of partial fixation of its footplate.

Fig. 6

Stapes footplate fixation without anterior crus. (A) Schematic presentation. (B) Removed stapes shows an underdeveloped anterior crus.

Fig. 7

Stapes footplate fixation without anterior crus and incus long process. (A) Schematic presentation. (B) Operative finding shows no incus long process and the stapes lacking anterior crus (arrow) without mobility of its footplate. c: chorda tympani; p: posterior crus.

Fig. 8

Stapes footplate fixation with obturator foramen obliteration. (A) Schematic presentation. (B) Removed stapes shows a non-perforated obturator foramen.

Fig. 9

Stapes footplate fixation without lenticular process: only fibrous band. (A) Schematic presentation. (B) Operative finding shows a fibrous band (arrow) instead of the lenticular process of the incus. c: chorda tympani.

Fig. 10

Stapes footplate fixation without stapes head. (A) Schematic presentation. (B) Operative finding shows only anterior (white arrow) and posterior crus (black arrow) without mobility of its footplate.

Fig. 11

Stapes footplate fixation with monopolar crus and without incus long process. (A) Schematic presentation. (B) Operative finding shows only one crus in the center of the footplate (arrow) and stapes-pyramidal fixation by a bony bar (asterisk).

Fig. 12

Underdeveloped stapes crura without oval window. (A) Schematic presentation. (B) Removed stapes shows underdeveloped crura.

Fig. 13

Anterior and posterior crura fusion without oval window. (A) Schematic presentation. (B) Removed stapes shows a crural fusion.

Fig. 14

No stapes and no oval window. (A) Schematic presentation. (B) Operative finding shows a long process of the incus (arrow) without the stapes, which is in contact with a downward facial nerve (asterisk) in the mesotympanum.

Fig. 15

No stapes and no oval window without incus long process. (A) Schematic presentation. (B) Operative finding shows shortening of the incus long process (arrow) without the stapes and downward displacement of the tympanic portion of the facial nerve with a bony bar (asterisk).

Fig. 16

No stapes and no oval window with incus long process fused to promontorium. (A) Schematic presentation. (B) Operative finding shows the long process of the incus fused to promontorium (asterisk) without the stapes and the oval window.

Fig. 17

Comparison of postoperative hearing results of congenital stapes anomaly according to status of stapes footplate (76 ears). Patients with mobile stapes or only stapes footplate fixation had significantly better hearing result than patients with stapes fixation associated with other ossicular anomaly or no stapes footplate. 1: Mobile stapes footplate with other anomaly; 2: Stapes footplate fixation only; 3: Stapes footplate fixation with other anomaly; 4: No stapes footplate with other anomaly; Good: postoperative air-bone gap <20 dB; Poor: postoperative air-bone gap ≥20 dB. Postoperative air-bone gap: postoperative air conduction-preoperative bone conduction.