Isolated unilateral congenital oval window atresia presenting as persistent conductive hearing loss: Diagnostic imaging

A 10-year-old girl with craniofacial malformation (cleft lip palate) and recurrent serous otitis media presented with persistent right hearing loss after multiple tympanostomy tube insertions. Otoscopy revealed aerated well-positioned long-term tubes. Audiologic evaluation was consistent with moderately-severe conductive hearing loss on the right ear with normal thresholds on the left.

Unenhanced high-resolution CT scan of the temporal bone revealed a bony place obliterating the oval window niche on the left, evident on both coronal and axial bone images, blocking the regular communication between the vestibule and the middle ear space and thus confirming the diagnosis of congenital oval window atresia (Fig. 1a). Right oval window was adequately fenestrated with in situ stapes footplate (Fig. 1b). Although we couldn’t exclude left facial nerve canal dehiscence on its horizontal tympanic segment in some coronal cuts, it didn’t show an inferior aberrant location that is frequently associated with oval window atresia. External auditory canal was patent, middle ear and mastoid cleft were aerated, the ossicles were normal and there was regular positioning of the incudomalleolar and incudostapedial articulations on both sides (Fig. 2a, b and 3a, b). Bilateral well-positioned and aerated Goode tympanostomy tubes were noted (Figure 4a, b). The remaining inner ear structures appeared normal.

Oval window atresia is an extremely rare congenital condition and its exact incidence is unknown. [1] It is characterised by the absence of an oval window in the presence of a bony plate superimposed between the vestibule and the middle ear cleft (Cremers class IVa anomaly). [2] It occurs bilaterally in 40% of patients. [3] Two embryologic theories have been suggested: failure of primitive stapes to fuse with the primitive vestibule and inferior displacement of the developing facial nerve, both precluding normal oval window development. [4]

Patients are typically children presenting with non-progressive moderately-severe conductive hearing loss since birth (air-bone-gap>40dB). [1] Clinical information provided by the otolaryngologist, namely the characteristics of the hearing loss and otoscopic findings, can help the radiologist. Timely diagnosis of oval window atresia helps surgeons predict hearing outcomes for children under speech and language development and guide its management.

CT scan is the best imaging technique to evaluate patients with suspected oval window atresia, aiding in both diagnosis and surgical planning. The usual rectangular shape of the oval window niche is obliterated with either a thick bone plate or concentric narrowing along the medial tympanic wall. There is an intimate relationship between the development of the oval window and that of the stapes footplate, horizontal segment of the facial nerve canal and vestibular portion of the otic capsule. In this perspective, associated classic imaging features include stapes absence or malformations (failure to identify both crura on axial CT images or stapes displacement from the oval window niche) and, less frequently, incus malformations. An abnormal more inferior course of the horizontal portion of the facial nerve, running over the oval window, commonly associated with dehiscence of its bony canal, is also frequently present. [1-4]

Treatment options include conventional or bone-anchored hearing aids placement and, in selected cases, surgical correction. Operative techniques including vestibulotomy or oval window drilling with prosthesis placement are demanding and risky as there are few landmarks for the vestibule and the displaced exposed facial nerve is at risk for injury. [5]

Take Home Message: Children presenting with maximal conductive hearing loss in the absence of other external and middle ear conditions or persistent irrespective of adequate acquired middle ear conditions treatment (e.g. tympanostomy tube insertion for recurrent otitis media with effusion), should be evaluated with a CT scan to exclude congenital malformations such as oval window atresia, mainly if other risk factors are present, such as craniofacial abnormalities.

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