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Superior Canal Dehiscence Syndrome (SCDS)

A diagnosis of superior canal dehiscence syndrome (SCDS) may raise many questions. Review the questions and answers below to learn more about the conditions, testing, diagnosis, treatment and recovery. 

Causes of SCDS

I have been told my brain pulsates against the bone and this is what has caused bilateral gaps in the bone. Will this get progressively worse?

We have to first admit that we do not know for sure what causes SCDS. My own research suggests that this is a congenital problem – when one is born with thin or missing bone over the superior canal (SC) because this is the last part of the inner ear bone to develop in the fetus and infant. Perhaps there is a premature arrest in the development of that bone. This bone defect alone is not enough; something else has to happen to stretch the dura to allow pressure to actually be transmitted between the brain cavity and inner ear. That might be a head injury or a sudden intracranial pressure change due to heavy lifting, a violent cough or a sneeze. Or it might just be the slow pulsation of the brain and cerebrospinal fluid over time. If you have had a cholesteatoma that raises all kind of issues, and I can only say that you need to be seeing a neuro-otologist who is well versed in all of them to sort this out.

Have there been any hereditary studies linking SCDS to other head and neck illnesses with a patient having multiple diagnoses or members in one family having multiple head and neck illnesses?

We have not seen much familial tendency to SCDS. Anything that causes trauma to the skull could start the pressure transmission if thin or missing bone was already present over the SC.

Are there any links between SCDS and Myalgic Encephalopathy (Chronic Fatigue Syndrome)?

We have not seen any direct relationship between SCDS and autoimmune disorders affecting the joints. However, it is not uncommon for patients with SCDS to complain of neck stiffness or pain. One interesting thing is that the vestibular system also partly controls the tone of the neck muscles. It is obvious in a few cases (about 10%) in which patients will have involuntary rapid head movements in response to loud sounds. However, most patients do not get this. Still we suspect that there are some corrupted vestibular signals affecting of the tone of the neck muscles in many patients. A number of patients have reported that their neck feels better after they recover from their SCDS surgery.

Do you find any connection with SCDS and osteoporosis and osteopenia?

We have not seen a connection, but this has been suggested by other researchers. I will mention that the vast majority of our patients do not have osteoporosis.

Symptoms

Brain Fog: Can you discuss “brain fog” as it relates to SCDS?

Patients often report cognitive deficits with SCDS. We can only assume that this is because the "bandwidth" of the patient's cognition is being taken up with just trying to stay balanced or make sense of the distorted hearing. My colleague, Dr. Yuri Agrawal, is doing some fascinating research on the relationship between vestibular disorders and impairment on performing visuo-spatial tasks. This suggests that the brain needs accurate vestibular information to create a map of the physical world in which to function. Anything that hinders that automatic mapping is going to weigh down the cognitive processes in the brain that have to work more consciously to correct the map of the world.

Head Pressure: Do you know what causes the head pressure (not the ear pressure per say but generalized head pressure) in those with SCDS?

I have to say this continues to baffle me. The classic teaching is that the inner ear has no pain fibers and can only produce a sensation of ear pressure in addition to, of course, hearing changes, tinnitus or vertigo. However, it is possible that ear pressure is just not well localized in some people. Another possibility is that the head pressure reflects the stretching of the dura into the superior canal dehiscence or through a defect in the neighboring tegmen bone. Finally, SCD seems to be a pretty good trigger for migraines, and I would consider an atypical migraine presentation to explain this.

Head Pain and Tegmen Defects: I have been diagnosed with SCDS, but also experience stabbing pains in my head when I cough, sneeze, or clear my throat, bend over.

In general, SCDS should not cause pain. When patients complain of pain, I usually look for another explanation. That does not mean you cannot also have SCDS! One possibility is that there is also a defect in the tegmen, the bone separating the brain cavity from the middle ear and mastoid. If the dura, the lining of the brain, herniates through this and gets stretched with these activities (because they increase intracranial pressure), that could cause brief pain.

Head Pain and Tegmen Defects: Is there some way of seeing testing for Tegmen?

Tegmen defects should also show up on CT, but the same caveat applies that CT can make bone appear to be absent there just as it can over the SC.

In general, SCDS should not cause pain. When patients complain of pain, I usually look for another explanation. That does not mean you cannot also have SCDS! One possibility is that there is also a defect in the tegmen, the bone separating the brain cavity from the middle ear and mastoid. If the dura, the lining of the brain, herniates through this and gets stretched with these activities (because they increase intracranial pressure), that could cause brief pain.

Migraines: I have been diagnosed with SCD but also suffer from migraines it. What is the long-term prognosis if I choose NOT to have MF surgery?

Sadly, your story is not uncommon! I will say in general to keep in mind that SCD is a mechanical problem - a hole in the inner ear that permits abnormal transmission of pressure between the inner ear and brain cavity. Once that starts, it is not likely to get better on its own. One's ability to tolerate it may change over time, however. I will also say that we often see SCDS symptoms trigger migraine symptoms. This gets tricky because migraine and SCDS symptoms can overlap - vertigo, sound sensitivity, ear fullness, nausea, etc. Here is where it is very important to be working with an experienced neuro-otologist who can sort out the symptoms - what is due to SCDS and what might not be. I have had several cases in which treating migraine symptoms first gave the patient enough relief to avoid surgery. Finally, I warn all of my patients with both SCDS and migraine that operating on the dura through the MF approach will probably trigger more migraines if they are not under optimal control to start.

Migraines: I was diagnosed with a dehiscence with migraines by my doctor. My symptoms of autophony and hyperacusis hearing loss stopped after 3 months of constant intolerable pain. Will it come back? I only have migraines now.

Your story illustrates a very important point: Migraine can itself cause many of the same symptoms as SCDS and frequently overlaps with SCDS. If the symptoms spontaneously stopped, it is more likely that migraine was the main source. You will want to talk to your physician about prevention strategies.

Diagnosis

What are the main tests/scans you use in order to judge whether a person is a good candidate for surgery?

First, I want to say that just as important as any tests/scans are the history and examination. I can often diagnose SCDS without any tests or scans, just by hearing the story and examining for nystagmus (rhythmic eye movements) in response to sound or pressure changes. If I see something that could only be explained by excitation of one of the superior canals, I already know what my tests will show! However, most cases are not so clear-cut, and I depend on the following:

1. A Good Audiogram. Now you might think that all audiograms are the same - after all, there is a national standard for doing audiograms. However, there is an unusual feature of SCDS: conductive hyperacusis. This is an ability to hear bone conducted sound not only better than air conducted sound but also better than most people ever could. This results in thresholds for hearing bone conduction that are actually below 0. Some audiometers are only calibrated to measure bone conduction hearing down to 0 decimals. If the audiologist is following protocol, they will not attempt to measure bone conduction below zero. If this is not taken into account; the audiogram could completely miss the presence of negative bone conduction, a key finding for diagnosing SCDS!

2. Tuning Fork Testing. Although some would consider this to just be confirmatory for the audiogram, I think it is very important in demonstrating which ear has conductive hyperacusis or, if both ears have it, which one is worse.

3. VEMPs (Vestibular Evoked Myogenic Potentials). These are tiny responses of various muscles when the inner ear balance organs are stimulated by sound or vibration. The classic VEMP is the cervical VEMP - a reflex measured from the sternocleidomastoid muscle in the neck in response to click sounds in the same ear. VEMPs can also be stimulated with tone burst sounds, and even with taps on the forehead. Our research has shown that the ocular VEMP in response to sound allowed us to best separate ears without SCD from those with the disorder. Unfortunately, it can sometimes be a challenge finding a place that does VEMP testing well. Part of the problem is that equipment manufacturers have been slow to seek FDA approval for their existing evoked potential systems to measure something new. (If the FDA finds something amiss in the application, they could pull an otherwise profitable system off the market, so why take the risk.) Those of us who do the testing have worked out our own systems and standards, but they vary a little bit from one place to another.

4. Examination for Nystagmus. In my practice, I do this with my own eyes, but one could record the eye movements with videonystagmography (VNG) to see if the eye movements in response to loud sounds or pressure changes in the ear canal or head cause the eye movements we expect from exciting the superior canal.

5. Electrocochleography (ECoG). We tend to use this mostly in the operating room for monitoring hearing function, but it’s certainly a reasonable test to do before surgery if you are in a place that does it a lot and does it well.

6. CT Scan. There is a lot that goes into making a good CT and also into making a misleading CT – one that can suggest a dehiscence when there is not one there. There is no perfect CT, and one should never make the diagnosis of SCDS based on the CT alone. That is why all of these other tests are listed.

Importance of VEMPS (Vestibular Evoked Myogenic Potentials)

Can you speak to the importance of VEMPs for diagnosis of SCDS? I have read that scans should not be used alone. Unfortunately, VEMPS may not be an option for some patients (prior neck surgeries, etc).

I would be happy to address the need for VEMPs in diagnosis of SCDS. However, please refer to the Diagnosis section to learn about all the testing that is needed. Basically, it comes down to this: CT scans will show absent or thin bone over the SC in about 1% of the population. Now nowhere near that many people have SCDS. For a dehiscence to produce the syndrome there has to be actual pressure transmission between the inner ear and brain cavities. All of these tests measure some version of that; they are the proof that an SCD is not just an incidental anatomic finding. Incidentally, neck (cervical) VEMPs are not the only option: Our research has shown that the ocular VEMP in response to sound allowed us to best separate ears without SCD from those with the disorder.

I have been wondering, what is the decibel threshold for a normal VEMP?

VEMP - vestibular evoked myogenic potential – testing is an important part of the workup of SCD. While there are changes in cervical VEMP thresholds depending on age, and other factors, we usually consider a threshold around 100dB to be "normal". A typical patient with SCD will have a lower threshold, such as 70dB. However, we have done some research showing that ocular VEMPs are more accurate than the cervical VEMPs in the diagnosis of SCD.

Procedures

Middle Fossa (MF) vs. Transmastoid (TM) Procedures: Could you explain why you prefer the Middle Fossa Craniotomy surgery for SCD repair and why you prefer the specific technique that you use rather than less invasive approaches?

I prefer the middle cranial fossa approach for several reasons. First, you can see the dehiscence directly with the middle cranial fossa approach. With the transmastoid approach, you cannot see the dehiscence. You have to assume that you are operating on either side of it when you drill open the semicircular canal and plug it. Which brings up a second problem that you have to drill on the canal and potentially to apply suction to the perilymph. I think that this is a real risk for causing more damage to the inner ear. Finally, with the transmastoid approach, you are forced to place the plug closer to the ampulla, which is the sensory epithelium of the semicircular canal. I feel that the closer you get to this structure, the more likely you are to cause damage to the neurons or hair cells in it. This damage would result in greater loss of function and plugging alone. For these reasons, I prefer the middle cranial fossa approach.

That being said, I do use the transmastoid approach as well, and there are good reasons to use it in some cases.

Transmastoid (TM) Cartilage Cap: Do you feel the Transmastoid Cartilage Cap is ever successful? What material do you use via Mid Fossa Repair? What is the deciding factor?

Please read my response to Round Window Reinforcement and Occlusion and I hope you will understand the essential importance of getting a watertight closure of the dehiscence. I am skeptical that resurfacing alone can do this in most cases, so I combine plugging (using one's own fascia, bone dust and bone chips) with resurfacing using bone cement. The bone cements are not perfect - they can crack, release from the skull base, be reabsorbed - and we don't know if they are toxic to the inner ear if left in contact with perilymph for years and years. Therefore, I prefer plugging plus resurfacing as a "belt and suspenders" approach.

Round Window Reinforcement (RWR): Please provide your thoughts on why round window reinforcement (niche) and round window occlusion do not really address resolving symptoms for SCD.

Normally the inner ear has only two "windows" - i.e. routes for sound energy to enter and exit. At the oval window, sound pressure comes in (and out) because the stapes moves in (and out) like a piston. This can only make fluid move in the inner ear if there is another mobile window. That is normally the round window, located at the bottom of the cochlea. This arrangement dictates that essentially all of the inner ear perilymph fluid movement caused by sound goes down the channels of the cochlea and out the round window. The waves of fluid movement in the cochlea are what move the basilar membrane and stimulate the cochlear hair cells; this is how we hear. If there is an additional opening somewhere in the inner ear, then we have a “third mobile window.” This is essentially a leak, and it allows fluid to move in the balance part of the inner ear (the labyrinth) in response to movement of the stapes caused by sound or pressure changes. This causes two problems: (1) the fluid movement that should be happening only in the cochlea in response to external sounds is reduced, and you have a hearing loss for air-conducted sound; (2) the fluid in the balance organs, which should only move in response to head movement, is inappropriately moving when the head is still. Results: hearing loss/distortion and vertigo.

ANY treatment for SCDS has to successfully address the inescapable physics of this situation. Plugging or watertight resurfacing the dehiscent SC restores the normal high impedance (opposition to flow) of the SC to this fluid flow, (i.e. it closes the leak). So what does ‘reinforcement’ of the round window (RW) do? To my understanding, it should increase the impedance of the RW and shunt even more of the fluid flow into the superior canal – exactly what we do not want!

So how did this procedure of RW reinforcement ever get started? As best I can tell, it was observed that for years before we knew about SCDS, patients were getting RW reinforcement for presumed perilymphatic fistulas. We later learned that some of these patients actually had SCDS, yet some of them seem to have improved with the RW procedures (this was suggested to me by Dr. Dennis Poe, whom I respect greatly). It is possible, however, that these patients also had reinforcement grafts placed around the oval window (stapes), causing enough of a conductive block between the eardrum and inner ear to blunt any vertigo from loud sounds. At any rate, the suggestion of RW reinforcement was taken up by some excellent colleagues looking for less invasive procedures to offer patients with SCDS. I am yet to be convinced by the limited data on this procedure. I have not done it because (a) it does not make sense to me, (b) I’m not so sure it is reversible, and (c) direct surgical repair of SCD has worked so well for so many.

I am not saying that I condemn RW reinforcement; future studies may prove me totally wrong on this. I should again point out that inner ear fluid dynamics are complex - they depend on the frequency or pitch of the incoming sound, and what may be true at one frequency of sound may not be true at others. The present assumptions on both sides of this argument about what RW reinforcement actually does are pretty inadequate, in my opinion. Dr. Heidi Nakajima, a colleague at the Massachusetts Eye and Ear Infirmary, is just starting to look at this and give us real data. I hope we know more in a couple of years.

Round Window Reinforcement (RWR): Have you reversed many Round Window Occlusion procedures? What is the rate of success to gain back the hearing loss caused by this procedure? Can the reversal be done at the same time as Middle Fossa?

I have not done RW reinforcement, nor have I attempted to reverse it. Depending on how it was done, trying to reverse it could tear the RW membrane and lead to severe hearing loss. The best person to remove the window reinforcement is the surgeon who put it there because they know in detail the materials and the situation at the time of the surgery.

Treatment for Hyperacusis Bone Cement Reabsorption: I am worried about residual hyperacusis after my next Middle Fossa not being resolved. Do you recommend white noise hearing aids if vertigo is resolved, but hyperacusis and low tone hearing loss remains? Can the body absorb bone cement?

There are a number of treatments for tinnitus/hyperacusis, and they have to be tailored to the patient. This might include white noise, environmental masking, Audionotch therapy or other selectively filtered music listening, medications, etc. Sometimes the best treatment for tinnitus is a hearing aid for the remaining hearing loss. Can bone cement be re-absorbed? I can only assume that it can, and that is why I generally try to use both plugging and resurfacing to avoid recurrence.

When is it Time to have Surgery?

Is there an age limit that you will not operate?

No! We do not believe in an absolute age limit. We do certainly, in every case, take medical history into account when considering someone’s ability to undergo general anesthesia.

How do you define “debilitating symptoms”? When would you recommend managing symptoms versus surgery?

Just as beauty is in the eye of the beholder, debilitation is in the eye (or maybe the ear!) of the sufferer. Some patients with vertigo in response to loud sounds can avoid these sounds – maybe they have a quiet job and no young children. However, others simply cannot and find that they are avoiding situations to the detriment of their career growth, family life, etc. We are noting that the constant symptoms of SCDS, like autophony and pulsatile tinnitus, are often the things that most debilitate patients and motivate them to choose surgery. Every patient is unique, and you have to have a good discussion with your neurootologist to decide if surgery is right for you at this time.

Alternatives to Surgery

I have recently been diagnosed with SCDS and am trying to find something other than surgery to help alleviate symptoms. Is any research being done to find a way to trick the body into recognizing SCDS as an injury so that the body may heal itself like it would a broken bone?

Occasionally a ventilating tube in the eardrum can help, but usually it only helps patients who note that ambient pressure changes are the major trigger for their symptoms.

As to self-repair, I am a big fan of that in general, but you should know that the inner ear bone is one of the only bones in the body that will not grow or repair itself after birth. There is a good reason for that – growth of that bone can fix the stapes in place and cause hearing loss; we call that disease otosclerosis. Therefore, I am not too encouraged that any treatment will get bone to grow over a superior canal dehiscence.

Why Do Most People Choose to Have Surgery?

Do you recommend surgery for people who are not experiencing significant dizziness or vertigo, and, while impacted by the disorder, are not disabled? In addition, in your experience, what percentage of patients who did not have much dizziness or vertigo prior to surgery have ongoing struggles with it post-op?

While I cannot get into specifics about individual cases, I would tell you that there are many patients who elect to have surgery because of autophony and pulsatile tinnitus. These do tend to improve with surgical repair. Surgery certainly causes some dizziness, but usually in a very specific fashion in terms of eye slippage during head movement in the plane of the superior canal. With physical therapy, this is greatly improved. The vast majority of patients do well after surgery in terms of dizziness and vertigo, including those who did not have pre-operatively.

Post-Operative Recovery and Care

How are patients followed after surgery and how you stay involved in helping them navigate through any post op issues? How is this best done with patients who live far away?

We tell patients to take six weeks off work. They need to not lift or strain or do anything that can increase intracranial pressure during that time. However, they can typically drive after about two weeks and can start doing aerobic activities in a matter of about three weeks. We usually see patients back at six weeks after surgery, but if they live a long distance away, we may agree to see them at three months if all is going well at six weeks. It is usually fine to fly one week after surgery and again by six weeks. We ask patients who do not live locally to plan to stay in Baltimore for a week after surgery. We see them one week after the procedure and remove the staples and sutures.

Post-Surgery Symptoms

Symptoms: What should people expect to experience after SCDS surgery? Can you talk about post-operative onset of autophony symptoms?

Almost all ear surgery results in fluid/swelling/blood within the middle ear cavity. This causes several symptoms, many of which can be quite similar to SCD symptoms, like hearing loss, fullness in the ear, autophony, and hearing bodily sounds. We normally expect this fluid to resolve in 8 weeks, but that is an average, and some patients can take up to 3-4 months to fully recover. After that time point, if they are still experiencing symptoms, then they should follow up with their surgeon.

Symptoms: Approximately, what is the window of healing from a transmastoid (TM) surgery? Is it normal to show progress and then have reoccurring symptoms such as a packed ear (fullness), dizziness, being off balance reappear off and on 6-7 months later? What tests are needed to see if a surgery has been successful and how often should patients be retested?

For either transmastoid or middle fossa (MF) approach to repair SCD, I tell patients to expect a recovery period of about 6 weeks. For the MF approach, the initial postoperative recovery is a little more involved because of the added recovery from a craniotomy in addition to the inner ear work. However, the tail end of the recovery is similar for both and really reflective of the work needed to get the brain to compensate for the decrease in balance function in the operated ear. During the recovery, there is often ear fullness immediately after surgery due to fluid and/or blood clot in the middle ear. Because of this, patients can still have pulsatile tinnitus, conductive hearing loss, autophony, and all of the other maddening auditory symptoms of SCDS, and I find myself having to be very reassuring at this point. This usually clears in a few weeks, sometimes suddenly and with a dramatic decrease in pressure and improvement in hearing. For whatever reason, a number of patients report that autophony can come back temporarily for a few months after surgery. This may reflect some degree of reabsorption of calcium from the bone dust/bone chips used in plugging or in bone cement used in resurfacing. But the formation of the final scar tissue may be the last step that resolves this symptom, and it may lag behind the calcium reabsorption. This is completely speculative, I have to admit, but a return in autophony is not unusual and should not be interpreted as a catastrophe. (Easy for me to say, I know!) I usually wait at least 6 months after surgery before doing investigations to see if something might have really “failed.”

Post-Surgery Pulsatile Tinnitus: I had transmastoid surgery and would like to know if the post-operative pulsatile tinnitus and very loud ringing tinnitus which are really troubling me at eight weeks after surgery are likely to clear up or if you have found this is a consequence of surgery that I may be stuck with?

As always with residual symptoms after surgery, I would advise that you discuss this with your surgeon. I will say that autophony and pulsatile tinnitus often continue for a number of weeks after surgery (either MF or TM approach) due to fluid collecting in the middle ear. This can still get better! However, please talk to your surgeon.

Post-Surgery Autophony: If your SCDS has been successfully plugged but you still suffer from autophony, what other causes are possible?

In these cases, we first look at the integrity of the repair with a good exam, repeat imaging, VEMP testing, and audiogram. In addition, we consider other possible causes like patulous Eustachian tube (see response to Patchalous Eustation Tube and SCDS).

Post-Surgery Face and Head Pain: I had Middle Fossa to repair a left SDCS. The plate and side of my head is still bothering me and most troubling is the nerve pain in behind my eye and down into my jaw. When will these symptoms subside?

You should definitely discuss these things with your surgeon. It is not uncommon in a few months after middle fossa craniotomy to have jaw pain and/or stiffness because that is when scar tissue can build up in the healing temporalis muscle. You may need stretching exercises for the jaw, physical therapy, or to see an oral surgeon for evaluation.

Post-Surgery Vertigo: I had a Middle Fossa craniotomy on my left side and had no issues for about a year after surgery. But now I have vertigo issues daily yet all of my SCDS tests have come back good. I still do vestibular therapy. I am bilateral but have none of the other symptoms. Can you recommend any other fixes for vertigo?

Sorry to hear this. Vertigo in general is very common – about 7% of the population will get vertigo at some point from some cause or other. It is usually not SCDS, so do not assume that any recurrent vertigo = SCDS. It is important to get a good evaluation for other potential causes.

Post-Surgical Vestibular Therapy and VOR (Vestibular Ocular Reflex): Can you share your thoughts on the importance of vestibular rehabilitation after surgery?

Vestibular physical therapy is a key part of the treatment of SCDS, as this can alleviate oscillopsia after plugging surgery. Vestibular PT will consist of gaze stabilization exercises and may include gait and postural exercises. The goal is to actually get your brain to experience the deficit caused by plugging the dehiscence (which is not a complete deficit – read more). The brain will only make changes to fix an error in the vestibular reflexes if it is forced to experience the error. Therefore, yes, vestibular PT is somewhat like any exercise – no pain, no gain. However, a properly supervised regimen of vestibular PT by a qualified therapist should not make you feel so bad that you do not want to continue. In the end, it is what will probably get you better the fastest. To find a therapist, I recommend >a href="http://www.vestibular.org/">www.vestibular.org, the website of the Vestibular Disorders Association. Look for the section called, “Find a Vestibular Specialist.”

Playing Wind Instruments Post Surgery: I have had two mid fossa surgeries and a round window reinforcement on right side as well. As a professional wind instrument musician, I have not been able to play for the past two years due to my symptoms prior to the surgeries and now after. Will I ever resume playing my instrument?

Vestibular physical therapy is a key part of the treatment of SCDS, as this can alleviate oscillopsia after plugging surgery. Vestibular PT will consist of gaze stabilization exercises and may include gait and postural exercises. The goal is to actually get your brain to experience the deficit caused by plugging the dehiscence (which is not a complete deficit – read more). The brain will only make changes to fix an error in the vestibular reflexes if it is forced to experience the error. Therefore, yes, vestibular PT is somewhat like any exercise – no pain, no gain. However, a properly supervised regimen of vestibular PT by a qualified therapist should not make you feel so bad that you do not want to continue. In the end, it is what will probably get you better the fastest. To find a therapist, I recommend >a href="http://www.vestibular.org/">www.vestibular.org, the website of the Vestibular Disorders Association. Look for the section called, “Find a Vestibular Specialist."

Long-Term Results from SCDS Surgery: I have SCDS that doesn’t impact my quality of life too heavily, and am otherwise healthy. I’m hesitant to have Middle Fossa Craniotomy surgery to correct my dehiscence if it will not last. What resources can you share or point me to that reveal the results of patients long term? The fear of complications or a failed surgery keeps me from "choosing" to go ahead with a MFC.

First, I have to say again that we cannot give specific recommendations in this forum. I would refer you to your neuro-otologist to know when it is safe for you to go back to these activities. In general, we have seen a few wind-instrument players with SCDS. We are not sure if years of blowing these instruments make it more likely that you would have symptoms - perhaps by increasing intracranial pressure and stretching the dura over the dehiscences - or if just being exposed to the pressure changes and sound gives you more opportunities to experience SCDS symptoms than if you did something else for a living. At any rate, in my practice I would evaluate VEMPS and the audiogram after surgery, and would consider repeat imaging, before making a decision on this question.

Other Surgery Questions

What do you do with the patients that do not get better after surgery and vestibular rehab?

In general, after 6 months for recovery and vestibular PT, I would repeat the investigations (refer to Diagnosis). I have also found a very specific MRI protocol to be helpful in assessing the integrity of the SC plug (if that was done). It is important to investigate whether vestibular function beyond that of the SC has been affected (with VEMPs, ENG or VNG, vHIT testing, exam). Finally, it is good to set aside all assumptions and go back to the initial symptoms - was it really SCDS in the first place? Or vestibular migraine, Meniere's disease, BPPV, chronic subjective dizziness, or something else?

Once you have surgery, is it possible for more holes to open up and you have to redo the surgery?

Let me make some general comments about bilateral SCDS. About 30 to 40% of patients with SCDS have a CT scan showing evidence of dehiscence on both sides. It is very important to understand that just missing bone over the superior canal does not guarantee that one will have symptoms from it. There has to be transmission of pressure between the inner ear and brain cavity to actually have the syndrome. Obviously, there has to be a hole in the bone for this to even be possible. However, there also has to be sufficient elasticity of the dura, the lining the brain. I think that many patients with dehiscence in the bone over the superior canal still do not have the syndrome because the dura is not that pliable. I cannot emphasize enough that one should never have a surgical procedure just because the CT scan shows evidence of superior canal dehiscence or thinning. Other data need to also fit: the history, the audiogram, the vestibular testing (VEMPs especially) and findings from the physical exam. Our experience is that most patients who truly have bilateral SCDS actually have more symptoms from one ear and only need to have surgery on that ear to get relief of their symptoms. How do we determine which ear? -- again, we look at all of the data, and it's really critical that you have someone evaluating you who understands all of these tests and how to properly examine you for nystagmus and other exam findings of SCDS. I have had several cases in which an understanding of 3-dimensional eye movements and their relationship to the geometry of the semicircular canals was critical to determining the correct ear for surgery. For patients who have had surgery on one side and are symptom free or minimally symptomatic on the other side, I presently recommend annual follow-up testing with audiogram and VEMPs to see if things are evolving on the other side. In general, we do not frequently see this unless there is some kind of trauma to make the dura-dehiscence interface more pliable.

Can you explain why you think the RWR surgical approach could cause more SCDS symptoms by forcing the sound through the 3rd window? Would this be true as well with a PLF (Perilymph Fistula) repair? Could it cause increased auditory symptoms like a RWR?

Thanks for the question. It depends on what the surgeon does in the PLF repair. If the work is only on the oval window, then it probably will not shunt more energy to the dehiscence. However, if the round window is patched in such a way as to increase its impedance (how much it resists movement), then it could shunt more fluid movement to the dehiscence and that would be bad. I should point out that inner ear fluid dynamics are complex and they depend on the frequency or pitch of the incoming sound. The present assumptions about what these procedures do to either of the natural windows are pretty inadequate, in my opinion. Dr. Heidi Nakajima, a colleague at the Massachusetts Eye and Ear Infirmary, is just starting to look at this and give us real data. I hope we know more in a couple of years.

If one has only auditory symptoms and has middle fossa repair of SCDS what are the chances of having vestibular problems postoperative?

I am glad you asked this question because we often have to council patients who have mostly auditory symptoms about what to expect after plugging the superior canal. I apologize for getting technical in what follows, but I think it is important to first point out that plugging a semicircular canal does NOT completely eliminate its function; I think there is a lot of misunderstanding out there about that. In fact, plugging a canal actually decreases its function about 30 - 50% in the research that we have done. This has also been confirmed experimentally in work done by the independent labs of Richard Rabbitt and Sergei Yakushin and colleagues. What does this mean in practical terms?

The semi-circular canals are rotation sensors. The superior semicircular canal senses the rotation of the head downward and rolling toward the same side at the same time. For the left superior canal (SC) - imagine a bar going through your right eye socket and coming out behind your left ear, and imagine rolling your head downward around that bar. That is the motion that the left SC senses. In fact, the right posterior canal also can sense this movement. However, for very rapid downward head movements around this bar, the brain depends primarily on the left SC for the information needed to drive the reflex movement of the eyes called the vestibulo-ocular reflex (VOR). It is this reflex that stabilizes our vision when we make this head movement. So plugging the canal reduces your ability to sense that head movement and to stabilize your vision. Vestibular physical therapy can get your brain to use the information from other sensory systems, from the right posterior canal and even the residual signal from the plugged left SC to eliminate almost any sense of instability in your vision, posture or walking from the partial loss of SC function caused by plugging. This takes about 6 weeks of consistent vestibular physical therapy, but most patients really do not notice a deficit when they are done. However, we will always be able to see a deficit in the plugged SC when we test it very carefully in isolation with our rapid head movement tests.

For the patient with terrible imbalance caused by the constant pulsation of the brain and cerebrospinal fluid against the superior canal fluids in SCD, the effect of the plug is often a huge improvement in their overall sense of balance. However, for the patient with NO balance symptoms to start with, this makes for a more difficult decision – are the symptoms of autophony, pulsatile tinnitus, conductive hyperacusis, distorted hearing bad enough to warrant a surgery that will give them something they do not already have? That choice requires careful, honest discussion between the surgeon and the patient. The answer is usually 'yes,' but sometimes a patient needs time to reach that decision. You should never feel rushed in this; it takes some people years to reach that point.

Relationship between SCDS and Intracanial Hypertension: Can you provide your views on whether SCD causes intracranial hypertension (IH)? Can you explain the difference between having IH, and the temporary issue of increasing intracranial pressure when straining, and how Cerebrospinal Fluid (CSF) leaks are different to IH.

There is considerable confusion right now about this issue. So I appreciate the chance to summarize what we know and what is speculation. First, some basics: our brain and spinal cord are constantly floating in cerebrospinal fluid (CSF), a clear fluid that is made by the choroid plexus in the brain and re-absorbed by little tufts of capillaries in the arachnoid granulations, cauliflower-like tufts around the venous sinuses in the dura, the lining of the brain. But the container of this fluid – the skull and spinal column, lined by the dura – is normally fairly rigid. So if CSF builds up, the pressure in the container (the intracranial pressure or ICP) can go up. A number of things can go wrong to cause ICP to be too high: The production of CSF can be too high. The venous sinuses carrying blood out of the brain can become narrowed or clot off due to trauma or clotting abnormalities. Sleep apnea at night can cause the arteries in the brain to dilate to try and get more oxygen to it, only to cause the pressure to go up. If we gain too much weight, the pressure of our abdomen when we lay down causes venous blood to back up more in the brain. The problem with elevated ICP – intracranial hypertension (ICH) – is that it tends to magnify itself: when the ICP goes up, the venous sinuses running along the inside of the skull are pressed upon and further narrowed. Even less blood flows out at a time, driving the pressure up further. This can cause headaches, head pressure, and ultimately damage the optic nerve and vision. It is common for ICH to also cause turbulence in the venous sinuses near the inner ear, leading to pulsatile tinnitus. Sometimes this is the only indication that the patient has that something is wrong!

The membranes of the inner ear, like the brain, also float it a clear fluid (perilymph), and its pressure needs to be carefully regulated too. The perilymph communicates with the CSF via the cochlear aqueduct, a very tiny channel from the bone of the inner ear near the round window to the intracranial space. That channel does not normally allow for much flow because it is so long and narrow. This prevents us all from hearing every pulsation of our brain – well, those of us who do not have SCDS, at least. Interestingly, it seems that only about a third of adults have a cochlear aqueduct that is even open all the way according to a study by Drs. Gopen, Rosowski and Merchant. So, unless there is another communication that opens up between the brain cavity and the inner ear, the inner ear is generally well protected from sudden changes in ICP. Other potential routes of communication between the brain cavity and inner ear include incomplete closure of the end of the internal auditory canal where the nerve fibers come out to the cochlea, an enlarged vestibular aqueduct (a congenital abnormality), and – yes, SCD.

So that brings us to the question: What is the relationship of SCDS to ICH? The one thing I would say is a solid connection is that SCDS can mimic ICH because pulsatile tinnitus can occur in either disorder. But as to the proposition that ICH causes SCDS – that elevated pressure in the brain cavity actually erodes bone over the superior canal – I think there is presently little evidence for this. A recent paper out of the groups at Cincinnati and Yale (Schutt et al Otol Neurotol. 2015 Mar; 36(3):551-4) noted that body mass index was higher and risk of obstructive sleep apnea was higher in patients with SCD than in control patients. They concluded that SCD could be caused by increased ICP eroding the bone between the brain cavity and inner ear. However, they readily admitted that their study had limitations, not the least of which is that they did not actually measure ICP. To that, I would add that they also only based the conclusion that their patients had SCD on the CT scan alone; their methods do not say anything about VEMPs, audiograms, examination or any of the other critical tests that we want to see before concluding that someone has actual SCD syndrome. In fact, they reported a very high rate of finding SCD on their CTs (6 out of 100 adults), which is much higher than the incidence of SCDS in the population.

Please do not misunderstand – I respect these colleagues highly and think that they have put an important and worthy concept in the literature for us all to consider. My concern is that patients or other colleagues would read this and conclude that the story is complete, that all SCD is caused by elevated ICP, and that patients have to address two problems. The authors do not say this, and they acknowledge that more work needs to be done. It may turn out that increased ICP does not cause SCD. Rather, SCD could be associated with elevated body mass simply because SCDS makes any exercise feel bad, (many of you know that!), and that you are simply likely to gain weight over time if you have SCDS.

In my own experience, true ICH is very rare in SCDS. If a patient has vision changes, morning headaches, pulsatile tinnitus that changes with compressing the jugular vein, and especially if they have sleep apnea or are obese, I would investigate separately for ICH. Our own investigations suggest that SCD could be a congenital defect in the bone. Most SCD occurs at the top of the canal, which we found is the last spot in the temporal bone to develop during the fetal and infant period. A premature arrest in the development of that bone could explain an absent or thin layer of bone over the SC. On top of that, you have the dura, which is relatively stiff and resistant to transmitting pressure. If the opening in the bone is still sealed off by healthy, stiff dura, there may be no effective pressure transmission, and SCD syndrome (SCDS) will not be present – i.e., the patient won’t have autophony, vertigo with sound or pressure changes, pulsatile tinnitus, etc. They will just have an incidental finding of missing bone over the SC. Now if they suffer a head trauma or big pressure change between the ear and intracranial spaces, that might be enough to stretch the dura a little bit and make it start transmitting pressures to actually cause the syndrome. But only 30-40% of our patients reported such trauma, so we believe that it might also be possible that normal changes in ICP might be enough to stretch the dura over time. Remember that every time your heart beats a volume of blood is pumped into the brain, it expands, and the ICP jumps up slightly. As the heart relaxes, the blood flows out, the brain shrinks, and the ICP drops. When most people talk about ICP, they are talking about an average pressure, not these peak and trough pressures. It may be that the most important thing in stretching the dura to start SCDS symptoms is not the average pressure, but the difference between the high and low pressures, or how quickly the pressure changes. Sorry for the long-winded answer, but I hope you can now see that there is a lot about this subject that we still do not know. It certainly is important to consider possible ICH along with SCDS if the right history is there, but I do not think there is much evidence to suggest that all or even most cases of SCDS are associated with abnormal elevations of ICP.

Additional Factors

Eustachian Tubes and SCDS: I am wondering how SCD can affect the Eustachian tubes. Ever since my SCD symptoms started my ears a full and pop constantly, why does this happen?

SCD itself does not affect the Eustachian tubes, but can produce symptoms that feel similar to those we encounter when we have problems with our Eustachian tubes, like when we feel congested from a cold. When our Eustachian tubes do not regulate pressure well, sound transmission to the inner ear can seem distorted and internal noises may sound louder than usual. This happens with SCD as well. Regarding the popping sensation, it may be that the usual pressure regulation functions of the Eustachian tube now sound much louder than before the SCD symptoms were present.

Bilateral SCDS: This is for those with SCDS in both ears, bilateral SCDS. How do you know which ear is causing most of the symptoms?

Let me make some general comments about bilateral SCDS. About 30 to 40% of patients with SCDS have a CT scan showing evidence of dehiscence on both sides. It is very important to understand that just missing bone over the superior canal does not guarantee that one will have symptoms from it. There has to be transmission of pressure between the inner ear and brain cavity to actually have the syndrome. Obviously, there has to be a hole in the bone for this to even be possible. However, there also has to be sufficient elasticity of the dura, the lining the brain. I think that many patients with dehiscence in the bone over the superior canal still do not have the syndrome because the dura is not that pliable. I cannot emphasize enough that one should never have a surgical procedure just because the CT scan shows evidence of superior canal dehiscence or thinning. Learn more about diagnostic testing.

Other data need to also fit: the history, the audiogram, the vestibular testing (VEMPs especially) and findings from the physical exam. Our experience is that most patients who truly have bilateral SCDS actually have more symptoms from one ear and only need to have surgery on that ear to get relief of their symptoms. How do we determine which ear? Again, we look at all of the data, and it's really critical that you have someone evaluating you who understands all of these tests and how to properly examine you for nystagmus and other exam findings of SCDS. I have had several cases in which an understanding of 3-dimensional eye movements and their relationship to the geometry of the semicircular canals was critical to determining the correct ear for surgery.

Hearing Loss and SCDS Surgery: I have not had any surgery yet, however my hearing in my left ear has deteriorated and the tinnitus is louder. If I were to have surgery, would this prevent my hearing from getting any worse or even give me back my hearing?

This depends very much on the nature of the hearing loss. SCDS does not generally cause sensorineural ("nerve") hearing loss, but rather conductive hearing loss. That generally improves with surgery. It's very important that you go over this with your consultant there and discuss whether your particular hearing loss can improve with surgery.

Hearing Aids and SCDS Surgery: Have you done Middle Fossa surgeries on patients who already wear hearing aids from sensoneural hearing loss? Do you see special issues in patients with hearing aids and is anything done differently for them?

This has not come up a lot, but I see no immediate reason why a person using conventional hearing aids could not have SCD surgery. There may be some time period after surgery when they could not wear the aid on the operated side until healing was complete. There is the theoretical issue of whether underlying sensorineural hearing loss predisposes the ear to damage. This is something you will want to discuss with your surgeon for your particular type of loss.

Surgery on SCDS Ear when Other Ear is Hearing Impaired: I had a middle fossa craniotomy and have bilateral SCDS. What is your opinion about surgery on the other ear when there is a severe hearing loss in the first ear?

It is a difficult situation when one ear is damaged and the other has SCDS. There are just so many variables here; you should get an opinion from one of us who does a lot of SCD surgery.

Pulsatile Tinnitus and SCDS: I have a type of tinnitus in my right ear that is quiet when my face is relaxed. The moment I open my mouth, and the wider I open it, this tinnitus roars and gets louder. Can you talk about the connection between tinnitus and SCDS?

The most common type of tinnitus seen with superior canal dehiscence syndrome is pulsatile tinnitus. The "pulsatile" refers to the fact that the tinnitus sound, which is usually a "whoosh"- occurs at the same time as your pulse (this is usually easy to check on yourself). Tinnitus that only occurs as the mouth is opened may be related to a spasm of one of the palate muscles, which is called palatal myoclonus. You can check for this by looking at your palate with a flashlight in the mirror, and seeing if you see you palate quivering. While we have not noticed a connection between that type of tinnitus and SCD, SCD does amplify your own bodily sounds, and therefore you may only be able to hear the sound because of the SCD.

SCDS Result of Trauma vs. Congenital Do you find it more difficult to treat someone with a dehiscence caused by head trauma versus congenital?

I have not noticed any difference in outcomes based on whether or not the patient has a history of some head trauma.

If it is Not SCDS What Else Could it be? Have you seen SCDS not being pressure and sound induced but more of a constant swimming drunk feeling? Have you seem someone like me with the visual neuro issues get better with surgery?

It is very important during the workup of SCD to look for other diseases that can cause similar symptoms. The most common one fitting that bill is migraine, which can also co-occur with SCD. Mal De Debarquement syndrome can also cause similar symptoms to migraine and SCD. What I would tell you is that SCD can certainly be an incidental finding on CT scans, and that the diagnosis of SCD is made based on history, physical exam (and we prefer to look at the eyes with infrared goggles while administering sound and pressure to the ear during the exam), vestibular testing including VEMPs, and audiometry. We do see a fair number of patients who are referred because of CT scan findings of dehiscence, but their symptoms are clearly due to other disorders.

I had SCDS in right ear, but several specialists diagnosed me with Patchalous Eustachian tube. I had surgery done for the dehiscence but nothing is better! My question: are the symptoms of the two that similar, and what are my options?

There is overlap of symptoms from patulous Eustachian tube (PET) and SCDS, especially autophony. Usually it can be sorted out based on the history (e.g., PET patients hear their nasal breathing; that's rare in SCDS), from careful exam (e.g. seeing eardrum movements with the patient sitting up and breathing deeply through the nostril on that side vs. the nystagmus and conductive hyperacusis findings in SCDS) and testing (VEMPs, audiogram). You may want to seek another opinion as to the origin of your symptoms and make sure a thorough investigation is done from scratch.

Menière’s Disease, Hydrops and SCDS: How often or at what percentage have you seen patients that have SCDS also exhibit signs of Meniere's disease? In addition, have you experienced patients being misdiagnosed with one for the other? I ask because there are numerous online products/sources that seemingly use these two as though they were one in the same and this can become quite confusing.

I find that disconcerting! It is very rare that Menière’s and SCDS truly co-occur. Please see the following responses for reasons why many patients and doctors may have gotten confused about the issue of supposed "hydrops" in SCDS based on electrocochleography (ECoG) testing.

Menière’s Disease, Hydrops and SCDS: If you are bilateral and have surgery on your symptomatic ear what are the chances your other ear starts up with and without surgery, what are the chances symptoms are Menière’s or other conditions, and not the hole to begin with and how to differentiate between this and other diseases?

I have a number of materials that I share with patients to go over these questions. If you peruse the answers to some of the other questions here, I think you will find many of them. Let me just focus on the question of Meniere's vs SCDS here, because I think the science that fascinates us as neurootologist may have confused many patients. My colleagues at the U of Michigan did a groundbreaking study showing that patients with SCDS have elevated SP/AP ratios on electrocochleography (ECoG). This is the same finding that has long been reported in many patients with Meniere's disease. The experimental literature suggests that the SP/AP ratio in MD is elevated because of relatively high pressure in the endolymph compartment of the inner ear, as if too much is being made and/or not enough is being reabsorbed. The endolymph-containing membranes of the inner ear then balloon out into the surrounding perilymph, a condition called "endolymphatic hydrops." In SCDS, the opening is between the brain cavity and the perilymph compartment. Under the right circumstances, we presume that the perilymph pressure can be lowered by this communication. This might produce a form of hydrops due to the perilymph pressure being too low, not the endolymph pressure being high. However, the result on ECoG might be indistinguishable! This is NOT to say that MD and SCDS are the same; indeed, they are usually very different and distinct disorders, and I find that they rarely overlap. If you are told that you have both hydrops and SCDS, you might want to get another opinion. I am not saying that it cannot happen - it is just very rare in my experience. An experienced neurootologist should be able to sort this out with a careful history, exam and appropriate auditory and vestibular testing as well as the CT scan.

Have you found the electrocochleography (ECoG) test to be helpful in diagnosing a symptomatic dehiscence? Is there any connections between SSCD and hydrops either before or after surgery?

Properly done, electrocochleography can be helpful in the diagnosis of SCD. ECoG does typically show elevation of the SP/AP ratio as described by our colleagues at the University of Michigan. There has been some misunderstanding that this indicates “hydrops” or buildup of endolymph in the inner ear. We believe that SCDS creates the same result not through high pressure in the endolymph compartment but through low pressure in the perilymph compartment because of the dehiscence. So, we do not have any evidence that hydrops, or Meniere's disease, predisposes to the development of SCD, nor that surgical repair of SCD predisposes to the development of Meniere's disease. We believe that during surgery, uncovering the dehiscence and plugging it can result in changes in pressure to the inner ear, so we do routinely use EcoG for monitoring hearing during surgery.


Patient Experiences: One-to-one with John Carey, M.D.

Hear stories from three SCDS at different stages of their treatment. Learn what to expect from your first appointment to recovery.