Round window reinforcement for superior semicircular canal dehiscence: A retrospective multi-center case series

Abstract

Purpose

To evaluate the outcome of round window (RW) tissue reinforcement in the management of superior semicircular canal dehiscence (SSCD).

Materials and methods

Twenty-two patients with confirmed diagnosis of SSCD by clinical presentation, imaging, and/or testing were included in the study. Six surgeons at four institutions conducted a multicenter chart review of patients treated for symptomatic superior canal dehiscence using RW tissue reinforcement or complete RW occlusion. A transcanal approach was used to reinforce the RW with various types of tissue. Patients completed a novel postoperative survey, grading preoperative and postoperative symptom severity.

Results

Analysis revealed statistically significant improvement in all symptoms with the exception of hearing loss in 19 patients who underwent RW reinforcement. In contrast, 2 of 3 participants who underwent the alternate treatment of RW niche occlusion experienced worsened symptoms requiring revision surgery.

Conclusion

RW tissue reinforcement may reduce the symptoms associated with SSCD. The reinforcement technique may benefit SSCD patients by reducing the “third window” effect created by a dehiscent semicircular canal. Given its low risks compared to middle cranial fossa or transmastoid canal occlusion, RW reinforcement may prove to be a suitable initial procedure for intractable SSCD. In contrast, complete RW occlusion is not advised.

Introduction

In 1911, Hennebert recognized that a sign of otosyphillis included dizziness and/or nystagmus provoked by pressure via pneumatic otoscopy (Hennebert’s sign). In 1929, Tullio described a related phenomena where sound provoked nystagmus and dizziness (Tullio’s phenomena). It became evident that such inner ear hypersensitivity was not specific to otosyphilis but could be associated with bone erosion of the semicircular canals, most commonly of the horizontal canal secondary to cholesteatoma. Cawthorne and others suggested as early as the 1940’s that the pathophysiologic mechanism was creation of a “third window” to the inner ear [1]. Symptoms included dizziness, tinnitus and hearing loss.

In the realm of inner ear hypersensitivity, Victor Goodhill in 1967 described perilymphatic fistulas (PLF) following total stapedectomy [2]. He and others went on to popularize controversial theories surrounding the causes of “spontaneous” PLFs and the potential benefits of patching the oval and round windows (OW, RW) with soft tissue. For the next two to three decades, ear surgeons perfomed tens of thousands of middle ear explorations searching for these fistulas but often with little evidence at the time of surgery of a definitive perilymphatic leak. Nonetheless, some of these patients who had “repair” of the OW and RWs noted unequivocal subjective improvement despite the absence of a visible leak.

In an attempt to preoperatively diagnose which patients might have a PLF, Hennebert’s sign was coopted to serve as a “fistula test”. In a positive test, pneumatic otoscopy pressure elicits objective eye movements (nystagmus or conjugate deviation) and/or a subjective sense of dizziness. Surgeons operated on many patients with vague atypical auditory and vestibular symptoms, but patients who had a “positive fistula test” appeared to have the highest chance of gaining subjective improvement despite no perilymphatic leak being found. Whether the benefit was due to a placebo effect or “microperilymph leaks” that could not be seen intraoperatively could not be determined.

Prominent voices began to decry the frequent repair of spontaneous PLFs despite the rare visualization of leaks including an article by Shea entitled “The myth of spontaneous perilymph fistula” [3]. The incidence of surgical explorations for PLFs subsequently diminished to a much lower frequency.

The correlation between these hypersensitivity phenomena and a dehiscent superior semicircular canal (SSC) was not noted until 1998 when Minor et al. described a series of patients with Tullio and Hennebert signs that also had an anatomical defect of the superior canal on high resolution computed tomography [4]. Thus, superior semicircular canal dehiscence (SSCD) syndrome was born. This newly recognized condition was characterized by sound or pressure-induced vestibular and/or auditory symptoms.

Symptomatic patients with SSCD often complain of vertigo resulting from loud sounds or visual bobbing (oscillopsia) in response to maneuvers that change middle ear or intracranial pressures [4]. Other presenting symptoms may include autophony (especially of one’s own voice), hyperacusis, chronic dizziness and/or imbalance, hearing loss (usually conductive), hearing distortion (often described as “tinny”), pulsatile tinnitus and aural fullness. Patients may also report the very strange phenomenon of hearing their own eye and neck movements, and even their own footsteps in the affected ear [5].

Surgical management of SSCD is reserved for patients in whom the symptoms are intrusive to daily living. These symptoms may vary from one individual to another. Some may complain bitterly about one isolated symptom such as pulsatile tinnitus while others may have the full constellation of auditory and vestibular symptoms mentioned above. Various options exist for either resurfacing or plugging the superior canal through either the middle cranial fossa or transmastoid approach.

In 1985, Jack Kartush, MD performed a study with Drs. J Kemink and M Graham on 60 cadaveric temporal bones to review middle cranial fossa anatomy focusing on the arcuate eminence and its use as a topographic landmark for middle cranial fossa surgery [6]. The publication noted that in 15% of temporal bone specimens, “there was no discernible arcuate eminence over the SSC. These specimens revealed variable depths of the SSC and degrees of temporal bone pneumatization”. In fact, SSCDs were noted in 2 of these specimens that had an absent arcuate eminence. Minor and colleagues [4], seeking a cause of an unusual constellation of otologic symptoms and vestibular signs, postulated that a dehiscent SSC could account for the symptoms. They identified the expected CT scan findings and reported the important connection between this anatomic abnormality and the constellation of symptoms that is now associated with SSCD syndrome.

Kartush, having incidentally noted the SSC dehiscences years ago, was prompted by Minor’s landmark publication to generate two hypotheses: 1) Some patients who underwent PLF “repair” in the past may have in fact had SSCD instead, and 2) Some of these patients may have benefitted from the “patching” not because a leak was being repaired but because a “third window” effect was being dampened — i.e. even though the SSCD was the abnormal window, symptoms might be reduced by altering the impedance of any of the three windows. Kartush described symptom improvement in 4 of 6 patients who underwent RW and OW reinforcement with temporalis fascia in a 2002 eMedicine® report [7].

In 2009, Silverstein published a case report of SSCD managed by complete occlusion of the RW niche using cartilage, bone wax and perichondrium [8]. The patient had complete relief of symptoms with no change in the conductive hearing loss. However, in two subsequent unreported patients, most of the symptoms became worse after complete RW niche occlusion and the patients required additional surgery to remove all of the tissue (Herbert Silverstein, MD, FACS, oral communication, 2012). Following revision surgery, the symptoms returned to preocclusion baseline. The data from these patients who underwent complete occlusion were not included in this study but the concept of reinforcing the RW rather than occluding the RW led Silverstein to more gently pack the RW niche.

Parnes and Poe, the other senior co-authors of this article, independently came to the same realization about the potential benefits of altering the compliance of the RW instead of the occluding the SSC and employed similar techniques to reinforce, but not occlude, the RW niche in SSCD syndrome. The following case series outlines the total collective experience of six surgeons in four centers using RW reinforcement to treat SSCD.