Complete round window niche occlusion for superior semicircular canal dehiscence syndrome: a minimally invasive approach.
Superior semicircular canal dehiscence (SCD) syndrome is a recognized condition associated with varying degrees of vestibular and auditory dysfunction. The authors present a case study of disabling SCD syndrome in a 37-year-old man who was successfully treated with a complete round window niche occlusion via a transcanal approach. This case represents the first report of a transcanal complete round window niche occlusion for the treatment of SCD syndrome. A brief literature review and discussion of surgical techniques follow.
Superior semicircular canal dehiscence (SCD) syndrome is a recently recognized condition that is characterized by varying degrees of sound- or pressure-induced vestibular or auditory symptoms. (1-7) SCD syndrome may occur as a result of bony dehiscence in the area overlying the superior semicircular canal. Affected patients often complain of vertigo secondary to loud sounds (Tullio phenomenon) or a visual sensation of viewed objects bouncing up and down (oscillopsia) in response to movements or maneuvers that change middle ear or intracranial pressures. Among the presenting symptoms are chronic dizziness, imbalance, hearing loss, pulsatile tinnitus, and aural fullness. Patients often report that their voice sounds unusually loud or like an echo (autophony), or they may notice a hypersensitivity to sound (hyperacusis). They may even report that they hear their own eye movements or their own footsteps in the affected ear. A subset of patients present with primarily auditory symptoms that may be discovered only after unsuccessful stapes surgery for presumed otosclerosis. (1-12)
In this article, we describe a case of SCD syndrome that was effectively treated with a minimally invasive complete round window niche occlusion via a transcanal approach.
A 37-year-old man presented with complaints of intermittent episodes of vertigo and dizziness that led him to suddenly collapse without losing consciousness. The patient said he had experienced at least 10 such episodes during the preceding year. The frequency of these events had increased in recent months. The first episode had been preceded by a loud noise and was associated with stooping and straining; the subsequent episodes were preceded only by stooping and straining. He noted no change in hearing, aural pressure, or tinnitus associated with these episodes.
The patient reported an 8-year history of a sudden-onset, nonfluctuating, left-sided hearing loss that had remained unchanged and a 1-year history of a gradual-onset, nonfluctuating, bilateral tinnitus (greater on the left) and a constant left-sided aural fullness and autophony. He also described hypersensitivity to certain sounds, reporting that he could hear the sound of his own footsteps in his left ear while walking and the movement of bones when rotating his neck. He admitted to unprotected noise exposure, and he had no known family history of hearing loss.
Physical examination demonstrated a normal-appearing right ear with an intact tympanic membrane, a clear middle ear, and good tympanic membrane movement with pneumatic otoscopy. On the left, the external auditory canal was normal, the tympanic membrane was intact, and the middle ear was well aerated. However, pneumatic otoscopy of the left ear produced vertical/ torsional nystagmus and subiective vertigo. Tuningfork testing demonstrated a positive Rinne test (AC > BC) on the right and a negative Rinne test (BC > AC) on the left at 256 and 512 Hz. A vibrating 256-Hz tuning fork was heard in the left ear when it was placed on the left medial malleolus.
[FIGURE 1 OMITTED]
Audiometric testing demonstrated a left-sided low-frequency conductive/mixed hearing loss with subnormal bone conduction thresholds at 250 Hz (figure 1, A) and intact acoustic reflexes. Vestibular testing demonstrated an enhanced vestibular evoked myogenic potential (VEMP) with lower thresholds on the left side. High-resolution computed tomography (CT) of the temporal bone confirmed the bony dehiscence overlying the left superior semicircular canal (figure 2). After a review of the history, findings, and test results, a diagnosis of left SCD syndrome was made.
We reviewed the disease process, prognosis, and treatment options with the patient and informed him that his symptoms had been caused by a mobile third window in his inner ear. The treatment options included (1) a middle fossa craniotomy with resurfacing or closure of the superior canal dehiscence, (2) a transmastoid superior canal occlusion, (3) a transcanal occlusion of the round window niche, and (4) continued observation. We also discussed the risks, benefits, and alternatives to treatment, as well as the complications of round window niche occlusion, which include bleeding, infection, hearing loss, dizziness, worsening tinnitus, tympanic membrane perforation, and injury to the chorda tympani or facial nerve. The patient understood that his symptoms might remain or might even become worse following treatment, but he also understood that the procedure was minimally invasive and could be reversed if he was unhappy with the result. He elected to undergo round window niche occlusion.
[FIGURE 2 OMITTED]
The senior author (H.S.) performed a transcanal round window niche occlusion with general anesthesia. After vertical canal incisions were made at the 6 and 12 o'clock positions, a traditional stapes flap was elevated. The bony posterior canal was enlarged with high-speed drill curettage, which allowed for ample visualization of the ossicular chain, round window niche, chorda tympani, facial nerve, and hypotympanum (figure 3,A). The bone overlying the round window niche was removed with a diamond drill for further exposure of the round window membrane (figure 3, B). A small piece of tragal cartilage and perichondrium was harvested through an incision on the medial aspect of the tragus. Perichondrium was removed, and a 2-mm biopsy punch was used to create a circular piece of cartilage. The cartilage was cut to approximately 1 mm thickness.
[FIGURE 3 OMITTED]
The round window niche was then occluded in three layers. The previously harvested tragal cartilage disc was trimmed to fit and then placed against the round window membrane (figure 4, A). Palpation of the incus revealed slight movement of the cartilage within the round window niche. Bone wax was gently placed over the cartilage and round window niche (figure 4, B), and care was taken not to invaginate the round window membrane. After the round window niche was sealed, palpation of the incus revealed no movement of the bone wax. A layer of perichondrium was then placed over the bone wax and promontory to provide further reinforcement of the complete round window occlusion (figure 4, C). The tympanomeatal flap was then reapproximated along the posterior canal wall, and the external canal was packed in the usual fashion.
Packing was removed after 1 week, and the patient was evaluated again at 2, 6, and 10 weeks postoperatively. At the 1-week evaluation, he said his dizziness, autophony, and hyperacusis had completely resolved, he had experienced no recurrent vertigo, and his left-sided aural fullness had abated significantly. However, he did note a slight decrease in hearing and a slight increase in tinnitus in his left ear.
At 6 and 10 weeks postoperatively, the patient remained vertigo-free and without dizziness/imbalance or collapse on straining or loud-noise exposure. Examination of the left ear revealed an intact tympanic membrane and aerated middle ear space. Pneumatic otoscopyofthe left ear failed to elicit symptoms of vertigo or nystagmus. A vibrating 256-Hz tuning fork placed on the medial malleolus was no longer heard in the left ear. The left-sided aural fullness, autophony, and tinnitus remained completely resolved, and his hearing had returned to preoperative levels. The patient could no longer hear his footsteps during walking, nor could he hear bony movement with head rotation. Subjectively, the patient's symptoms were completely resolved, and he was very pleased with the results of the procedure.
Postoperative audiometry at the 6-week follow-up demonstrated intact auditory reflexes bilaterally and resolution of the subnormal bone conduction in the left ear at 250 Hz (figure 1, B). Findings on VEMP testing remained abnormal, with a lower threshold and enhanced amplitude in the left ear.
Much has been written about SCD syndrome since Minor et al first described the vestibular symptoms associated with this condition in 1998. (1) Patients with this syndrome experience various vestibular and/or auditory manifestations. Diagnosis relies on the history, physical examination findings, and testing. Typical symptoms include sound- or pressure-induced vertigo, disequilibrium, oscillopsia, autophony, aural fullness, and hearing loss. Examination and testing may reveal sound- or pressure-induced torsional/vertical nystagmus in the plane of the affected superior canal, hyperacusis to bone-conducted sound, a conductive hearing loss with intact acoustic reflexes, and an enhanced VEMP (lower thresholds) in the affected ear. Bony dehiscence overlying the superior semicircular canal on the symptomatic side is evident on high-resolution CT of the temporal bones. A vibrating tuning fork may be heard in the affected ear when it is placed on the ipsilateral medial or lateral malleolus. (5,7,12)
Some patients complain primarily of auditory symptoms and report no specific vestibular symptoms. These patients have occasionally been identified after unsuccessful stapes surgery for correction of presumed otosclerosis. Various authors have attributed some of these failures to an inner ear conductive hearing loss. It is believed that this conductive hearing loss occurs secondary to the presence of a mobile third window in the inner ear; a third mobile window may lessen air-conduction thresholds and increase bone-conduction thresholds less than 0 dB HL in the lower frequencies. (7,9,12-22) Evaluations in an animal model have supported this proposed mechanism. (23-25) Patients with SCD syndrome may be distinguished from patients with otosclerosis and ossicular fixation by the presence of an intact acoustic reflex and an enhanced VEMP. (12)
[FIGURE 4 OMITTED]
Recent research has led to an improved understanding of the mechanism underlying SCD syndrome. Temporal bone studies suggest that the bone overlying the superior semicircular canal may be dehiscent in as much as 0.7% of the population and less than 1 mm thick in another 1.3% of individuals. (3) Dehiscence of bone overlying the membranous superior semicircular canal may lead to a mobile pathologic third window within the inner ear. (11,15) Sound or positive pressure arriving via the external ear or middle ear may result in movement of the round and oval windows. This may lead to endolymph movement within the inner ear directed toward the site of dehiscence overlying the superior canal. (1,4,5,10) The resultant endolymphatic movement leads to deflection of the superior canal cupula away from the utricle (ampullofugal flow). This leads to an increase in the firing rate (stimulatory) of the afferent neurons that innervate the ampulla of the superior canal. Eye movements and nystagmus occur in the plane of the superior canal according to the Ewald laws. A vertical-torsional nystagmus is noted in the plane of the superior canal. Fast-phase vertical nystagmus is directed down, and torsional nystagmus of the superior pole of the eye is directed toward the affected ear. Negative pressure changes at the site of the round and oval window or increases in intracranial pressure may also result in movement or pressure changes within the inner ear. These pressure changes transmitted through the site of superior canal dehiscence toward the round and oval window result in eye movements occurring in the opposite direction. (1,4,5,10) Eye movements may not correspond to the affected canal in cases of bony dehiscence of more than 5 mm or in cases of hypofunction of the superior canal. (4,10)
An awareness of SCD syndrome is crucial in the consideration of appropriate differential diagnoses. Other disorders that may mimic SCD syndrome include a patulous eustachian tube (pET), temporomandibular joint syndrome, serous otitis media, eustachian tube dysfunction, perilymphatic fistula, benign paroxysmal positional vertigo, Meniere disease, and allergic disease. (8,12) Patients with these disorders may present with a variety of overlapping signs and symptoms similar to SCD syndrome. A thorough evaluation will help distinguish SCD syndrome from other processes.
The symptoms of pET may closely mimic SCD syndrome. Lying down in both conditions may relieve patients' symptoms. (12) While autophony, aural fullness, and a conductive hearing loss may be present in both conditions, a low-frequency conductive hearing loss with subnormal bone conduction, intact acoustic reflexes, and an enhanced VEMP on the affected side should heighten the suspicion of SCD syndrome. High-resolution CT of the temporal bone will help confirm dehiscence overlying the superior semicircular canal in the affected patient.
Treatment options vary depending on symptom severity. Continued observation, avoidance of provocative stimuli, and supportive measures such as vestibular rehabilitation or vestibular suppressants have been suggested for patients with minimal or minor symptoms. Surgical treatment is reserved for patients with disabling sound- or pressure-induced vertigo, imbalance, or oscillopsia. Standard surgical options include (1) middle fossa craniotomy for superior canal occlusion or resurfacing and (2) transmastoid superior semicircular canal occlusion. (2,5,6,8,10,12,16,17,26) In both cases, the superior semicircular canal is addressed through occlusion or resurfacing techniques. This effectively eliminates a pathologic third mobile inner ear window at the site of the superior semicircular canal. Short- and long-term results vary depending on the approach and procedure.
Various risks and complications have been reported with both major surgical approaches. Besides the inherent risks of a middle fossa craniotomy and temporal lobe retraction, reports suggest that middle fossa repair of superior canal dehiscence may result in sensorineural hearing loss in cases of revision surgery and in patients who have undergone previous stapes surgery. (21) Canal occlusion--via either atransmastoid approach or middle fossa approach--does carry a small but real risk of resultant global vestibular hypofunction in addition to a risk of sensorineural hearing loss. (27) As a result of these possible complications, surgical correction is often used only in patients with severe or disabling symptoms. In an attempt to avoid these risks, both D.S. Poe, MD (written communication; February 2009) and J.M. Kartush, MD (oral communication; February 2009) have suggested fascia reinforcement of the round and oval windows in a procedure similar to perilymphatic fistula repair. This maydampen the hypercompliance of the round and oval windows and decrease the sensitivity of the inner ear to sudden fluctuations in sound or pressure. (26)
The senior author has advocated complete round window niche occlusion in an effort to eliminate the effects of a pathologic third mobile inner ear window.
Over the course of 4 years, a technique was developed for occlusion of one of the three mobile inner ear windows at the site of the round window rather than the superior semicircular canal. The intent was to develop a minimally invasive alternative to more-invasive surgical procedures. This technique was developed as the result of a desire to devise a readily reversible procedure that poses little or no risk to the patient's hearing.
Complete round window niche occlusion may be performed via a transcanal approach--similar to a stapedectomy--thus avoiding a middle fossa craniotomy or transmastoid approach. If the procedure is unsuccessful, it can be easily reversed; the fascia, cartilage, and bone wax occlusion of the round window niche can be removed with little risk of damage to the inner ear. More-invasive techniques might then be reserved for patients in whom the minimally invasive round window niche occlusion fails. Offering round window niche occlusion prior to resurfacing or superior canal occlusion through a middle fossa craniotomy or transmastoid approach might allow for treatment of patients who have previously declined or may not be candidates for major surgical procedures.
Complete round window niche occlusion differs from other previously proposed minimally invasive procedures. As opposed to decreasing oval and round window compliance with fascia, complete round window niche occlusion with cartilage, bone wax, and perichondrium directly eliminates the mobility of the round window. Elimination of the third-window effect occurs, thus reestablishing a two-window system between the oval window and the site of canal dehiscence. This occlusion results in resolution or improvement of symptoms associated with SCD syndrome.
In conclusion, the authors of this report achieved dramatic results by performing a complete multilayered closure of the round window niche in a patient with disabling SCD syndrome. This readily reversible, minimally invasive approach may offer an alternative to more-invasive surgical procedures. Based on our review of the literature, it appears that ours is the first reported case of a minimally invasive complete round window closure for the treatment of symptoms associated with SCD syndrome. Our preliminary results are encouraging, and further evaluation of the outcomes of this technique is in progress.
Note: Since the completion of this case report, the senior author has treated a second patient with SCD syndrome and similar symptoms by performing a complete closure of the round window niche in a similar fashion. Unfortunately, the patient's symptoms became worse, and a transmastoid superior canal occlusion was performed. Results are not yet known.
The authors thank Julie Daugherty, MS, ARNP, for her contributions to the preparation of this manuscript.
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Herbert Silverstein, MD, FACS; Mark J. Van Ess, DO
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Silverstein, Herbert; Van Ess, Mark J.|
|Publication:||Ear, Nose and Throat Journal|
|Article Type:||Case study|
|Date:||Aug 1, 2009|
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