Timothy C. Hain, MD • Page last modified: November 2, 2021
Basically, one can either avoid things that make you dizzy or cause hearing related symptoms, or you can get an operation. The conservative approach (watch/wait) is outlined here. The surgical approaches are outlined next.
As an overview, the main route of surgery for SCD is "middle fossa". This means that the skull is opened up, the brain is retracted, repair (e.g. roofing or capping) and/or plugging is done of the defect in the bone that defines SCD, and the skull is closed again. A fairly major process that requires retracting the brain. . The other main route for SCD surgery is "transmastoid". This means that the surgeon approaches the dehiscence from the side rather than from the top. This is a more challenging for the surgeon but less invasive.
The "cutting edge" (pun intended) for SCD surgery are attempts to use less invasive procedures, such as endoscopy, possibly through the mastoid sinus. Again as a general rule, approaches that are less invasive are also less successful, as one cannot visualize the defect as well. Nevertheless, we expect that eventually this approach will become dominant, as surgical expertise and technology improves.
Zhang et al (2021) published an analysis how patients were chosen for surgery "a single tertiary care outpatient clinic", probably Johns Hopkins given that two of the three authors on this paper are from JH. They reported that low frequency conductive hearing loss and increased oVEMP amplitude "are the strongest predictive factors for making a diagnosis of SCDS and for choosing surgical repair." So in other words, if you go to Johns Hopkins, this seems to be how thye make their decision to operate. Note that we are NOT comparing two objective things here like "oVEMP amplitude", and CT scan results, but rather we are comparing many factors (at least 7), to a judgement of the cllinicians involved to operate. As an aside, we do strongly support the idea that increased oVEMP amplitude (we would say at least 20), is a good reason to look extra hard for SCD.
Vlastaros et al reviewed studies of SCD treatment (2009). The treatment of a dehiscence generally involves either closing the dehiscence (resurfacing, roofing or capping) or plugging of the canal. This is appropriate, for example, in superior canal dehiscence. Results are claimed to be good (Mikulec et al, 2005), although in a condition like this without clear cut objective endpoints, it might be difficult to be sure. Plugging of the canal is the direct approach with respect to dizziness. It eliminates the stimulation of the superior canal by pressure, and also eliminates the normal function of the superior canal on one side.
Middle fossa (top down) vs. Transmastoid (from the side)
Plugging can be done through the mastoid (side) or the middle fossa (top). As the dehiscence may include the entire top of the superior canal, one would wonder how the surgeon can always successfully plug the canal through the transmastoid route. Putting in a plug and then cementing it over makes a little more sense. Still not everyone's dehiscence is the same.
While better exposure is attained through the middle fossa, it is riskier overall as it involves entering the cranial vault, retracting the temporal lobe and lifting up the dura. Middle fossa procedures are far more expensive as well. Van Hasendonck et al (2015) reported excellent results with transmastoid plugging (2015). For dehiscences that are large, it would seem a little difficult to cap them using a side opening such as is the case with the transmastoid approach.
Capping refers to closing of the opening made for the plugging with cement, or closing of the dehiscence with cement. This procedure is intermediate in effectiveness compared to plugging (Vlastarkos et al, 2009). Plugging and capping would seem even more logical than plugging alone, although somewhat riskier.
The repair of the dehiscence using a bone or fibrous tissue graft (roofing, resurfacing) has risk as well-- sometimes dura is stuck to the membranes of the inner ear and an attempted repair results in deafness instead. Roofing or perhaps plugging and capping, however, would seem to be the logical approach to the hyperacusis of SCD, as one would think that the third window would remain open otherwise. "Boxcar" plugging -- putting a plug on both sides -- would seem to be a reasonable fix for hyperacusis. The outcome of using cartilage to "roof" SCD was reported by Afif et al (2019) in 10 patients, and the results were not encouraging. They wrote:
"However, four of 12 ears (33%) had a second (revision) surgery before achieving these results. Postoperatively, hearing through air and bone conduction tended to decrease at frequencies greater than 2500 Hz. The chance of avoiding a re-operation at 36 months (and up to 120 months) was estimated to be 57.1% (95% confidence interval [confidence interval]: 100%, 32.6%). The most common surgical complication was intraoperative cerebrospinal fluid (CSF) leak, encountered exclusively during dural elevation, seen in four of 12 ears (33%)."
In other words "redos" occured about 1/3 of the time, and spinal fluid leaks, also about 1/3 of the time. This may be related to the tegmen dehiscence commonly seen in patients with SCD (see elsewhere on this page).
Roofing (resurfacing) can also lead to recurrent symptoms due to shifting or resorption of the bone. For all of these these reasons, at this writing (2016), "plugging" with "capping" is favored (Vlastarkos et al, 2009). The best approach is usually the middle fossa. This is an evolving situation as of 2021 and we hope that better approaches are developed than just middle fossa.
We will discuss these one by one.
Lack of improvement:
Of course one expects to be better, and there are certainly some patients who feel no different, or perhaps even worse. Not much is written about this. We have several patients in our files who had "successful" SCD surgery, with no change in their symptoms. The operation was a success.... The main possibilities here are wrong diagnosis (something else than SCD is causing dizziness) or inadaquete surgery.
Loss of superior canal function
In the plugging type of surgery, there is some loss of function in the superior canal. This takes some time to adjust to. Patients who undergo surgery are unsteady for roughly 6 weeks after the repair (Janky et al, 2012). One would expect that younger individuals would do better. The loss of function in the superior canal is also expected to be accompanied by loss of fluid on T2 MRI in the superior canal, and a change in the VHIT test done for the superior canal. The latter is somewhat difficult to do. MRI of the superior canal is not difficult, but it is also common for radiology departments to omit the high-resolution T2 protocol, as it is out of their routine.
The surgeons here are explicitly working close to the dura, which is the membrane that holds spinal fluid (CSF) out of other places, such as the mastoid sinus. Afif et al (2019) reported about 1/3 of 10 cases developed a CSF leak. We don't think CSF leak is that common, but still it is to be considered.
We have never encountered a patient with complete deafness after SCD surgery, but we have heard of at least one case. There are several potential mechanisms. During any approach, separating the dura overlying the superior canal may be a problem, and one might open up the labyrinthine membranes should the dura be closely adherent. Additionally, when plugging the canal, one might cause a labyrinthitis and hearing loss. Just drilling around the inner ear can damage hearing.
Loss of all labyrinthine function
We have encountered a few patients who have had plugging done by very experienced surgeons, in which it appeared that a lot more damage was done than intended. It may be that plugging can sometimes lead to occlusion (clogging up) of more canals than anticipated. We have also encountered this situation in a patient who did not have plugging, but just roofing. We speculate that this surgery can occasionally provoke an immune response similar to a vestibular version of Cogan's with filling of the labyrinth with fibrous tissue. Fortunately this is rare.
Failure after a few years
We have also encountered patients where roofing failed after a year or two -- this seems to be common for roofing procedures where soft tissue is used for the repair rather than bone cement. . This leads us to continue to be conservative regarding recommendations for surgical intervention.
Round window plugging is a newly proposed surgery for SCD. The basic idea is that pressure changes in the inner ear can cause fluid shifts only if there there is a place for the fluid to go. There normally is a pressure relief part of the inner ear -- called the round window. When the stapes moves inward, the round window moves outward. When there is abnormal pressure presented to the opening in SCD, presumably the round window also moves back and forth and facilitates fluid movement. This is all quite logical. Several otolaryngologists have suggested that closing the round window, might be a successful treatment of SCD. The advantage of this method is that it is much less invasive than either the plugging or resurfacing approaches.
Recently, Silverstein and Van Ess reported a single case in which this approach was successful (Silverstein and Van Ess, 2009). The operative approach was do to a very thorough closure of the round window, using 3 layers. This is essentially what is done in perilymph fistula surgery, but using a more vigorous approach. It is too soon to know whether this method will be adopted. One wonders whether or not it might be reasonable to use an even more aggressive approach and "cement" the round window shut.
Biophysical modeling of SCD suggests that RW plugging should be ineffective.
We don't recommend round window plugging procedures.
We think it is not wise to seek SCD treatments that are "minimally invasive". Here we are explicitly talking about endoscopic approaches to SCD, usually guided with a navigation system. You want your surgeon to see what they are doing. Just because it can be done with an endoscope does not mean that it is as good as the standard approach. Whatever procedure you choose should have some good evidence behind it.
This is not an absolute rule. Small and easily accessible dehiscences might be reasonable for an endoscopic system (with navigation). Big dehiscences are less likely to be suitable for a minimally invasive approach.
New conditions can sometimes elicit entrepreneurial activity in surgeons. There currently is an oversupply of otologic surgeons in the United States. In the past, a somewhat similar condition to SCD (perilymph fistula), was associated with an immense surge in surgical operations, many later determined to be inappropriate. SCD, being a condition that can have slippery diagnostic criteria, could go this way. For example, is disturbing to see articles about SCD with obvious errors in their title such as this one from usnews.com: "https://health.usnews.com/health-news/patient-advice/articles/2015/09/30/a-new-treatment-for-super-semicircular-canal-dehiscence". "Super semicircular canal Dehiscence" ?
Safety tips prior to planning SCD surgery:
- Before you proceed surgical treatment for SCD, be sure you get an opinion from a physician expert who is not an ear surgeon, at another institution.
- There is no hurry to treat SCD with surgery. It is not life-threatening. Take your time and find a trustworthy and experienced surgeon. If someone wants to operate next week, take a deep breath, say you will think about it, and check with another expert (best at a different institution). There are many choices of otologic surgeons in the US.
- You should pick otologic surgeons who are experienced, mature, trustworthy, and well trained.
- By mature, we mean someone who has been in practice for between 10-30 years. Otologic surgery requires good hands, good eyes, and a good brain.
- By experienced, we would define this as > 100 SCD cases.
- Trustworthy is a more complex thing, but they should be well enough established that they do not need to recruit surgery patients through the internet.
- By well trained we mean that they did their otology training at a reputable place. In the US, this usually means one of the bigger ENT programs in the country. Be sure that they actually are otologists (i.e. ear doctors) as well.
- Popular does not necessarily mean reasonable. Having a good bedside manner is not necessarily the same as having good surgical skill.
While the diagnosis of SCD has become much easier in recent years, treatment has lagged behind. More work is needed to work out the best approach for treatment.