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Year : 2022  |  Volume : 28  |  Issue : 2  |  Page : 163-166

Absent Stapedius Muscle and other Rare Congenital Ossicular Anomalies: A Case Series

1 Department of ENT and Head and Neck Surgery, 158 Base Hospital, Siliguri, West Bengal, India
2 Department of ENT and Head and Neck Surgery , Army Hospital Research and Referral, New Delhi, India

Date of Submission23-May-2021
Date of Acceptance01-Oct-2021
Date of Web Publication21-Sep-2022

Correspondence Address:
Dr. Madhukar Upadhyay
158 Base Hospital, Siliguri - 734 014, West Bengal
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/indianjotol.indianjotol_71_21

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Conductive hearing loss due to ossicular anomalies is generally associated with external auditory canal dysplasia. Congenital ossicular anomalies in isolation are rare and often have a delayed diagnosis, particularly if unilateral. In such cases, the predominant symptom is conductive hearing loss and otosclerosis is usually the major differential diagnosis. We present a series of three cases of congenital ossicular chain anomaly. These patients were initially diagnosed as a case of otosclerosis. However, the diagnosis was revised based on intraoperative findings and managed accordingly.

Keywords: Conductive hearing loss, congenital ossicular anomalies, Cremer classification, ossiculoplasty, otosclerosis

How to cite this article:
Upadhyay M, Goyal S. Absent Stapedius Muscle and other Rare Congenital Ossicular Anomalies: A Case Series. Indian J Otol 2022;28:163-6

How to cite this URL:
Upadhyay M, Goyal S. Absent Stapedius Muscle and other Rare Congenital Ossicular Anomalies: A Case Series. Indian J Otol [serial online] 2022 [cited 2022 Nov 27];28:163-6. Available from: https://www.indianjotol.org/text.asp?2022/28/2/163/356457

  Introduction Top

Congenital deformities of the ossicular chain in isolation are a rare entity and even the most busy otology clinics have very limited clinical experience of the same.[1],[2],[3],[4],[5],[6] They generally occur in association with an external ear deformity or as a feature of more general condition or a syndrome like  Treacher Collins syndrome More Details.[3]

The most common presentation is a young individual with nonprogressive conductive hearing loss without any history of middle ear infection in the childhood.[1] Clinical examination reveals a normal appearance of intact tympanic membrane. Pure-tone audiometry findings are consistent with conductive or mixed hearing loss. Although impedance audiometry may be sometimes useful in the assessment of some of these conditions like congenital stapes footplate fixation where there is a type As curve, usually it is not contributory.[1] All these findings generally make the otologist to consider otosclerosis or ossicular discontinuity as major differential diagnosis. Since congenital anomaly of the ossicles is difficult to diagnose, a high index of suspicion is required in a young patient who presents with nonprogressive conductive hearing loss and an intact tympanic membrane. Further course in the management involves imaging in the form of a high-resolution computerized tomography (HRCT) of temporal bone mainly to assess the ossicular status and look for any inner ear deformity. It is also useful to rule out any middle ear pathology, congenital cholesteatoma or on rare occasions any vascular lesion as a cause of hearing loss.[1] Even with the aid of imaging, it is sometimes difficult to assess the exact nature of the disease, thereby warranting an exploratory tympanotomy. In cases where otosclerosis is established as the major differential diagnosis, the surgeon may plan for stapedotomy but during the course of surgery, the intraoperative findings may be in concurrence with various types of ossicular anomalies as popularly described by Teunissen and Cremer.[7] Hence, a thorough knowledge of the congenital ossicular anomalies and its management is must before exploring the middle ear. The aim of this case series is to enhance our knowledge about congenital ossicular anomalies as evident by the dearth of literature on the same.

Case 1

The first case is of a 22-year-old male with no known comorbidities who presented to the OPD with a history of hearing loss in left ear for the past 10 years. There was no history of obvious trauma, fever, exposure to loud noise, and ototoxic drugs and no history of any previous ear surgery. There was no history of any other ENT complaint.

On examination, there was no deformity of pinna or external auditory canal, and both the tympanic membranes were intact and mobile on seigelisation. Tuning fork tests showed conductive hearing loss in left ear. Rest of ENT examination was normal. In view of conductive hearing loss with intact tympanic membrane, we had differential diagnoses of otosclerosis and ossicular discontinuity. HRCT of the temporal bones revealed normal ossicular status, no evidence of any middle ear pathology, and normal anatomical landmarks [Figure 1]. The stapes footplate thickness was not commented upon.
Figure 1: HRCT Temporal bones

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Pure-tone audiogram (PTA) of four tone pure-tone average of 0.5 KHz, 1 KHz, 2 KHz, and 3 KHz revealed an air-bone gap (ABGap) of 28 dBHL in the left ear and normal hearing threshold in the right ear. Tympanometry showed a bilateral type “A” curve. Ipsilateral acoustic reflex was present on the right side while absent on the left side.

The patient underwent exploratory tympanotomy under local anesthesia through permeatal approach. The HRCT findings were corroborated with microscopic visualization of the middle ear. On cursory examination, middle ear mucosa was healthy with apparently normal looking ossicular chain. The round window reflex was absent both on tapping the malleus and incus. A closer view at the ossicles revealed multiple abnormalities of ossicles. The stapes superstructure was deformed. At the site of anterior crus, only a bony stud was present and there was no post crus giving an appearance of monopodial footplate. The facial nerve canal was found to be dehiscent although there was no overhanging facial nerve. The incus was found to be deformed and was removed. The body and short process of incus were hypoplastic and lenticular process was not present [Figure 2]. When stapes footplate was tapped, contrary to what was expected, it was found to be mobile and the round window reflex was elicited.
Figure 2: Deformed and hypoplastic incus

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Keeping in view the intraoperative finding of M + I-SS- with a mobile footplate, a decision to reconstruct the ossicular chain with long columella was made. The patient was managed with type 3b Tos tympanoplasty using total ossicular replacement prosthesis (TORP) between stapes footplate and tympanic membrane supported by tragal cartilage. The final diagnosis was revised to congenital ossicular anomaly with mobile stapes footplate (Cremer III).

Postoperatively period was uneventful. PTA done postoperatively at 12 weeks revealed closure of the AB gap. Subjectively also patient experienced improvement in hearing in the left ear.

Case 2

A 38-year-old female with no known comorbidities presented with hearing loss left ear for 9 years. There was no history of obvious trauma, fever, exposure to loud noise, and ototoxic drugs. There was no history of any other otolaryngologic complaint. The patient underwent myringotomy and grommet insertion in 2008 which was removed in 2011. The surgical documents for the above procedure were not available with the patient.

Otoscopic examination revealed intact and mobile tympanic membrane on both sides. PTA showed a conductive hearing loss on the left side with an air-bone gap of 49 dBHL and normal hearing thresholds on the right side. Tympanometry revealed bilateral type “As” curve. HRCT temporal bone did not reveal any obvious ossicular anomaly, however, the stapes footplate was thickened on the left side. The patient was diagnosed as otosclerosis and underwent exploratory tympanotomy under local anesthesia. Microscopic visualization of the ossicles revealed complete absence of stapes superstructure with a thickened stapes footplate and absent round window reflex. Furthermore, there was no differentiation between the annular ligament and the stapes footplate. CO2 laser (20 W, 0.7-mm spot size) assisted small fenestra stapedotomy with prosthesis (0.6-mm diameter × 4.5-mm length) insertion was done. Based on the intraoperative finding of absent superstructure and fixed stapes footplate, the diagnosis was revised to congenital stapes footplate fixation. Postoperatively, there was complete closure of the AB gap with subjective improvement in hearing.

Case 3

A 32-year-old male patient presented with complaints of bilateral hearing loss for 11 years. Otoscopic examination revealed bilateral intact tympanic membrane with tympanosclerotic patch on the right tympanic membrane. PTA revealed conductive hearing loss bilateral with air-bone gap of 20 dBHL and 30 dBHL in the right and left ear, respectively. The patient was planned for stapedotomy left ear. On microscopic examination of the middle ear, it was found that ossicles were normal in appearance with absent round window reflex, however, the stapedius muscle and tendon were absent. The stapes footplate was thickened and there was a lack of differentiation between the annular ligament and the stapes footplate. CO2 laser-assisted small fenestra stapedotomy and piston insertion was done.

  Discussion Top

The incidence of congenital anomalies of the ear is extremely rare with an incidence of < 1 per 15000 births.[1] Many authors tried to classify the congenital anomalies based on mostly case series, however, the most accepted classification is the one proposed by Teunissen and Cremer in 1991.[7] Minor congenital anomalies of the ear have been classified into four classes in this classification as mentioned under:

  1. Class I: Congenital stapes ankylosis without other deformities in the middle ear
  2. Class II: Stapes ankylosis associated with other congenital ossicular chain anomalies
  3. Class III: Congenital anomaly of the ossicular chain, but with mobile footplate
  4. Class IV: Congenital aplasia or severe dysplasia of the round window.

The above classification is based on the intraoperative findings and does not aid in preoperative diagnosis of the anomaly. The diagnosis is therefore difficult preoperatively and the surgeon has to consider differential diagnoses like otosclerosis and ossicular discontinuity as has been reported in our series. Among our three reported cases, our first case was a Cremer III and second was Cremer I. However, our third reported case could not be classified as per the present Cremer classification.

Among the four classes of congenital ossicular anomalies, congenital stapes footplate fixation with associated ossicular anomalies is the most common (38% in 144 cases).[7] The key to diagnosis of congenital stapes footplate fixation is nonprogressive conductive hearing loss with normal otoscopic findings.[8] Both our cases of congenital stapes footplate fixation had nonprogressive CHL in sync with the available literature. In the second case, the hearing loss was noticed only for the past 9 years which may be put as an argument against the congenital nature of the disease. It is noteworthy to mention that the patient's other ear had absolutely normal hearing thresholds which explains the delay in noticing her symptoms. The infectious or inflammatory origin of the ossicular problems in our case series can be safely excluded based on the findings of absence of otorrhea, persistent nonprogressive hearing loss, normal otoscopic findings, and normal HRCT temporal bone findings. In case of otosclerosis, the patient has slowly progressive conductive or mixed hearing loss with essentially normal otoscopic findings. On surgical exploration in cases of congenital stapes footplate fixation, the vascularity over the footplate is not found to be increased. The margins of the footplate and annular ligament are difficult to visualize since the footplate blends into the bone of the surrounding capsule.[8] The otosclerotic footplate has increased vascularity usually in the anterior area. The margins of the footplate and annular ligament are difficult to visualize anteriorly, however, they can be readily visualized posteriorly. The central footplate area is often thin with bluish discoloration. In the second and third cases we were surprised by the presence of stapes footplate fixation with complete lack of differentiation between footplate and annular ligament which made us to change our diagnosis to congenital stapes fixation.

The second case in our case series had the typical appearance of a congenitally fixed stapes footplate accompanied by rather unusual finding of complete absence of stapes superstructure. Similarly, the third case had the finding of stapes fixation with unusual finding of absent stapedius muscle and tendon. These findings are remarkable in the current scenario as even the Tos modification[9] of Teunissen and Cremer[7] classification does not describe these findings of absent stapes superstructure and absent stapedius muscle tendon.[9] From an embryological and developmental perspective, the stapes superstructure develops from the second pharyngeal arch cartilage and the stapedius muscle develops from the second pharyngeal arch mesoderm. Hence, both can be malformed in second arch anomalies or in combination with the first arch anomaly and present as isolated ossicular anomalies. Literature review shows that there are less than ten reported cases of absent stapedius muscle.[10] We suggest the inclusion of our reported finding in the existing classification of Cremer and Teunissen. We also recommend to include nonosseous middle ear ossicular anomalies like the absent stapedius muscle.

The treatment options in case of congenital ossicular anomalies range from hearing aids to surgical correction of the anomaly.[6] Cases suitable for hearing aid benefit from externally worn hearing aid, however, in the presence of chronic otitis media or external auditory canal anomaly, bone-anchored hearing aids is the alternative option. In our reported case series, all the cases were managed surgically. One of the patients was managed with TORP while the other 2 cases were managed with LASER-assisted stapedotomy and piston insertion.

  Conclusion Top

The present case series highlights the fact that owing to the rarity of congenital ossicular anomalies, surgeon exploring the middle ear for conductive hearing loss may be caught unawares leading to inadequate management. Therefore, a thorough and a comprehensive knowledge of existing anomalies will keep the surgeon better prepared to manage them. Although there is an existing classification for congenital ossicular anomalies, there is still scope of expansion to include newly reported anomalies.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Raveh E, Hu W, Papsin BC, Forte V. Congenital conductive hearing loss. J Laryngol Otol 2002;116:92-6.  Back to cited text no. 1
Swartz JD, Faerber EN. Congenital malformations of the external and middle ear: High-resolution CT findings of surgical import. AJR Am J Roentgenol 1985;144:501-6.  Back to cited text no. 2
Cousins VC, Milton CM. Congenital ossicular abnormalities: A review of 68 cases. Am J Otol 1988;9:76-80.  Back to cited text no. 3
Funasaka S. Congenital ossicular anomalies without malformations of the external ear. Arch Otorhinolaryngol 1979;224:231-40.  Back to cited text no. 4
Teunissen B, Cremers CW. Surgery for congenital stapes ankylosis with an associated congenital ossicular chain anomaly. Int J Pediatr Otorhinolaryngol 1991;21:217-26.  Back to cited text no. 5
Henner R, Buckingham RA. The recognition and surgical treatment of congenital ossicular defects. Laryngoscope 1956;66:526-39.  Back to cited text no. 6
Teunissen EB, Cremers WR. Classification of congenital middle ear anomalies. Report on 144 ears. Ann Otol Rhinol Laryngol 1993;102:606-12.  Back to cited text no. 7
House HP, House WF, Hildyard VH. Congenital stapes footplate fixation; a preliminary report of twenty-three operated cases. Laryngoscope 1958;68:1389-402.  Back to cited text no. 8
Tos M. Surgical solutions for conductive hearing loss. Vol. 4. Thieme; 2000.  Back to cited text no. 9
Wright JL, Etholm B. Anomalies of the middle-ear muscles. J Laryngol Otol 1973;87:281-8.  Back to cited text no. 10


  [Figure 1], [Figure 2]


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