Imbalance and Dizziness caused by Superior Canal Dehiscence Syndrome

 

Not too many people have heard about the Superior Canal Dehiscence Syndrome because it represents one extremely rare condition. Like the name of it already suggests - this syndrome is mostly characterized by vestibular (balance) symptoms. Experts are saying that these problems are directly caused by
(1) intense sound stimuli or
(2) by changes in intracranial or middle ear pressure.
This pressure in middle ear can be changed due to a dehiscence of the bony layer that covers the superior semicircular canal, one of the three semicircular canals responsible for maintaining the balance! However, although it is not so common, some individuals diagnosed with this syndrome only have hearing loss, and no imbalance symptoms.  

It is important to point out that the prevalence of complete dehiscence of the superior semicircular canal is approximately about 0.7% in the general population. However, we must point out again that not all patients with this syndrome have the syndrome symptoms, and because of that- experts still don’t know the exact percentage of symptomatic patients among them. If we talk about gender prevalence, then we should know that it is still not proven to be of statistical significance. Important is also that there was also no report of children being affected.  

Let me say something about the normal anatomy structures in the middle ear which are responsible for normal hearing and balance. First, it is important to point out that the whole system has 2 functional windows. This system is called the cochleovestibular system.

1.      The oval window. This gape, or window, is located at the footplate of one of the smallest bones in our body-the stapes. Its function is to allow sound to enter the inner ear. This part of the ear is also called the vestibule. What is the purpose of this opening? Well, it allows the mechanical wave to be transduced into neural activity because it is the only way a sound can be perceived.

2.      The round window function is a bit more controversial but mainly- it is considered to have several roles. Its first role is thought to involve the release of sound and mechanical energy from the tympani part of the ear. Another proposed role is its participation in the secretion and absorption of substances in the inner ear. 

Therefore, it is reasonable to assume that these 2 windows of the inner ear work together to regulate hearing and balance. It is important to understand that all this can work only like it was described! When we talk about a dehiscence in the superior semicircular canal, in that case- a third-window effect is thought to take place. What happens then? Well, it is simple- endolymph within the labyrinthine system continues to move in relation to sound or pressure, which causes an activation of the vestibular system.

What exactly is a cause of this condition? Well, it could be a very tricky question! Experts proposed several different theories. An embryological etiology of this syndrome has been proposed and by most- it is considered the most probable. According to this theory this condition is about a postnatal failure of bone formation over the superior semicircular canal. Some of the experts even used a computer to make one kind of a simulation model, determined that the cause of bony dehiscence of the superior semicircular canal was due to a malpositioned primitive otocyst-cell that later form the bone.  

 

Like we have already mentioned, not all patients with this syndrome have the symptoms, but when they do- these are the most common:

·         Dizziness:

The great majority of patients report unsteadiness. It is also specific that this imbalance increases with activity and relieves by rest. That’s why- people are often good in the morning, but as the day passes- their balance gets worse and worse. Besides these balance problems, some patients also reported ringing in the ears. Other patients experience problems only when they are coughing, sneezing, or blowing their noses. Experts are calling this form of disease the "Valsalva induced dizziness".

·         Pressure sensitivity:

It is completely normal that person feels sensations when going from the area with high to the area with low pressure. Such sensations are usually felt in airplane or when diving in big depts. The fact is that the changes in air pressure that occur in the middle ear normally do not affect inner ear. However, in a case of dehiscence syndrome, changes in middle ear pressure will directly affect the inner ear, stimulating the balance causing typical symptoms.  

·         Sound sensitivity

Great majority of patients also reported a special kind of sound sensitivity! It is not unusual for the patients with this syndrome to notice that use of ones own voice or a musical instrument will cause dizziness.

 

Most of the experts agree that the best diagnosis of the Dehiscence syndrome is being is being done using a high resolution temporal bone CT scan. Other tests are:

·         Valsalva test (the best, done in the office)

·         Tullio test (done in office, not very sensitive)

·         Fistula test (best done in office, but can be done in the lab)

·         Tympanometry may provide a solution

 

Laboratory tests that may be helpful (VEMP is most useful) are the following:

·         MRI scan

·         ECOG 

·         ENG 

·         Audiometry

·         Temporal bone CT scan, high resolution  

·         VEMP (Vestibular evoked myogenic potentials)

 

In most cases- the treatment is not necessary but surgical care is sometimes needed and, it is reserved for patients with severe disabling symptoms.  There are several forms of operation but the two are the most common: Middle fossa craniotomy and repair of fistula and the transmastoid superior canal occlusion.

Middle fossa craniotomy and repair of fistula
What's the most important thing about this procedure? Well, the patients undergo a middle cranial fossa craniotomy on the affected side after which the temporal lobe is gently retracted.  How to recognize the region of the superior semicircular canal? It is rather simple because it is always located with identification of the arcuate eminence. What a surgeon does when he finds it? A dehiscence of the superior semicircular canal can be covered with bone wax, bone cement, or fascia…

Transmastoid superior canal occlusion
When we talk about this procedure- we should know that Transmastoid superior canal occlusion is also one very good and effective surgical method of treatment. First, mastoidectomy, is being done, which means that the bone, located behind our ears, is being removed! After this part- the superior semicircular canal is identified near the ossicular heads. The superior semicircular canal is then ablated with a combination of tissue and fascia, like in the first form of operation!

Patients with this syndrome are extremely interested about the prognosis after the treatment, especially after the surgery! Well, here is some good news. Most experts agree that the success rate in the treatment of superior canal dehiscence is quite high. Some even claim that it could be about 95% which is extremely high! One expert with 20 patients showed remarkable results! 9 patients had canal plugging and 11 had resurfacing procedures! Complete resolution of all vestibular symptoms and signs was achieved in 8 of the 9 patients after the canal was plugged. 7 of the 11 with resurfacing procedures had resolution of their vestibular complaints.  

 

Here are some useful tips for both, those who had and those who didn’t but planning to have a surgical correction of their inner ear structures! Try to change your life style as follows:

1.      First, every patient should avoid loud nose. This means that there’s no playing instruments or loud singing for all the patients!   

2.      Patients should also avoid pressure fluctuations between ear and the rest of your body. Although it sounds rather simple- this isn't easy! How to do this? Well, patients should avoid weight lifting, straining to do things, or even strenuous sexual activity.

3.      Pressure fluctuations between middle ear and external ear should also be avoided! How? Well, to simplify - in other words, patients should avoid situations where ear might pop. These situations can happen for example on airplanes, when patients should wear ear plugs which showed to be often helpful. Sometimes, when these are not possible or available, experts suggest using a nasal decongestant at least one half hour prior to landing.

4.      Most experts agree that sometimes even a ventilation tube may help.  

5.      When we talk about possible medications that can relieve symptoms- we should know that in most cases they are not extremely useful. Sometimes benzodiazepines can help!