1

Introduction

Superior semicircular canal dehiscence (SSCD) may present with sound- or pressure-induced vertigo , vertigo with an associated conductive hearing loss , or a conductive hearing loss alone . A dehiscence of the bone overlying the superior semicircular canal is thought to be causative, acting as an effective “third window” into the inner ear.

Aspects of the hearing loss associated with SSCD can appear quite similar to those caused by otosclerosis or other ossicular disorders. However, given the fundamentally different mechanism involved in SSCD, the clinician must differentiate it from middle ear pathology to avoid ineffective and potentially injurious attempts at surgical correction. If the otologic surgeon is unaware of this possibility, a stapedotomy or stapedectomy may be attempted.

We report 3 cases of SSCD diagnosed only after failed surgical treatment of conductive hearing loss attributed to otosclerosis and discuss the hearing and vestibular outcomes of stapedotomy on SSCD patients.

1.1

Case 1

A 36-year-old white woman was referred by a community otologist for possible revision right stapedotomy. The patient had a 10-year history of tinnitus, eustachian tube dysfunction, and right-sided conductive hearing loss. She had undergone right tympanostomy tube placement 5 years previously and had a chronic perforation in the posterior inferior quadrant. She also related a history of mild disequilibrium with rapid head motion. She underwent an uncomplicated tympanoplasty and small fenestra stapedotomy with a Teflon wire piston for presumed otosclerosis. At surgery, the ossicular chain was noted to be stiff and the stapes footplate fixed. Postoperatively, the patient experienced decreased hearing and worsened episodic disequilibrium, particularly with straining, coughing, or change in altitude. Audiogram obtained after surgery showed a maximal conductive loss with an average air-bone gap of 40 dB and speech reception threshold (SRT) of 52 dB. Her word recognition score was 92% at 80 dB.

At our institution, examination of the right ear revealed a retracted tympanic membrane with an area of atelectasis onto the promontory. The wire of the prosthesis could be seen on the long process of the incus. Tuning fork examination (512 Hz) lateralized to the right ear, and bone conduction was greater than air conduction on that side. At presentation, the patient was 4 months pregnant; so diagnostic radiologic studies and possible further surgical management were deferred until after the delivery. Given her progressive vestibular complaints and persistent conductive hearing loss, the diagnosis of SSCD was considered. High-resolution computed tomography (HRCT) scan was obtained. Clear evidence of bilateral SSCD and a medially displaced prosthesis into the vestibule were noted ( Fig. 1 ). There were no otic capsule changes suggestive of otosclerosis. Audiogram now showed an average air-bone gap of 55 dB with SRT of 65 dB. Word recognition was 76% at 100 dB.

Reformatted high-resolution, noncontrast, coronal temporal bone CT scans of a patient who had undergone prior right stapedotomy for presumed otosclerosis (case 1). The study shows a dehiscent superior semicircular canal on the right (white arrow) and left (white arrowhead). The stapes prosthesis is shown within the vestibule on the right (black arrow). Normal left vestibule (black double arrow) is shown for comparison.

Because her troublesome vestibular symptoms were potentially the result of her prosthesis being medially displaced by a retracted tympanic membrane, the middle ear was surgically explored. The prosthesis was gently repositioned to an appropriate depth within the vestibule, a cartilage graft was used to reinforce the atelectatic tympanic membrane, and a tympanostomy tube was placed. Postoperative audiogram showed a moderate improvement in conductive hearing, with an average air-bone gap of 40 dB and SRT of 55 dB on the right. The patient’s vestibular symptoms were mildly improved as well, although she continued to be limited in her activities. Given this, she elected to undergo plugging of her superior canal via a middle fossa approach. The procedure confirmed the presence of a dehiscent superior canal. In early follow-up, her vestibular symptoms have improved, although she continues to limit her activity secondary to disequilibrium.

1.2

Case 2

A 56-year-old Indian man was referred by a community otologist for possible revision stapedotomy. The patient had a history of progressive left-sided mixed hearing loss and episodic disequilibrium. Preoperatively, the patient was noted to have an average air-bone gap of 40dB, an SRT of 60 dB, and 100% word recognition score at 80 dB. Acoustic reflexes were not tested. He had undergone an uncomplicated primary small fenestra stapedotomy with a Teflon wire prosthesis from which he developed a persistent tympanic membrane perforation. Postsurgical air-bone gap was unchanged at 40 dB with an SRT of 55 dB. The patient then underwent revision stapedotomy and tympanoplasty approximately 1 year later, performed by the same surgeon. At the time of the second procedure, the prosthesis was noted to be loose on the incus; and the mobility of the malleus was limited by several adhesions. The prosthesis was recrimped on the incus; and the adhesions were lysed with a CO ₂ laser, resulting in improved mobility of the malleus. Postoperative audiogram showed no improvement in hearing with a persistent air-bone gap of 40 dB and an SRT of 58 dB.

On presentation at our institution, physical examination revealed a well-healed left tympanic membrane. The patient related a history of disequilibrium and brief episodes of vertigo that predated his original surgery. The vertigo could be elicited by loud sounds and by the application of pressure to his left tragus. He also complained of distortion of sounds, describing a “vibration or echoing” on the affected side.

The diagnosis of SSCD was considered, and HRCT scan was obtained. This confirmed bilateral SSCD ( Fig. 2 ) with no radiologic evidence of otosclerosis. Because the patient’s disequilibrium is not disabling, he has opted for conservative management. He currently wears a hearing aid on the left with good result.

Direct coronal noncontrast temporal bone CT scan of a patient presenting with persistent conductive hearing loss following stapedectomy and revision (case 2). The study shows bilateral dehiscence of the semicircular canals (white arrows). Individual right and left images have been merged to create this figure.