Introduction
For over 100 years ear specialists have recognised that, in
certain conditions, the sound transmitted to the inner ear may
activate the vestibular (balance) system. The inner ear consists of
a cochlea (hearing component) and fluid-filled canals (balance
component). These normally work independently, however, patients with some
conditions or diseases have reported that sounds can cause vertigo
(spinning sensations) and nystagmus (eye movements). It is assumed
that the sound causes fluid in the balance canals to move, which
gives the person the impression that they are physically moving.
This can be a minor and temporary inconvenience or a major
disability. In many cases the imbalance disappears when the
underlying condition is addressed.
A new condition was discovered in the 1990's. which could not be explained by any known
disease or condition. Patients exhibited one or some of the
following:
Imbalance
Hearing loss
High sensitivity or intolerance to sounds of certain
frequencies or character (e.g. a mobile phone dial tone, a cry of a
child, a particular note on a church organ)
Motion Intolerance
An ability to hear internal sounds such as eye movements or
walking
X-ray and CT scans revealed that these people had a
dehiscence (thinning) of the bone overlying one of the balance
canals - the superior semicircular canal.
Sound normally moves the fluid in the cochlea which
activates the hair cells and converts the sound into electrical
signals. This same fluid is shared by the balance canals. Loud
sounds change the pressure of the fluid in the cochlea and the
canals. This may result in slight movement of the thinned bone,
which is interpreted by the brain as physical movement. If the
patient's eyes are open, visual cues tell the brain that there is no
movement. This 'confusion' results in feelings of imbalance. The
patient's eyes may also move suddenly in an effort to compensate for
this apparent motion.
The cause of the condition is not fully understood. There
appears to be a physical disposition to this condition, which is
triggered by a particular event. It can occur in one or both sides
of the head.
Diagnosis
Diagnosis involves a number of investigations, including a
comprehensive hearing test, tests in a vestibular clinic to assess
eye movement, and a CT scan. The direction of eye movement helps to
determine if the problem is on the left or right side. The thinning
bone can be seen on the CT scans.
Treatment
Patients seen by specialists at Ear Science Institute Australia
have been successfully treated in one of two ways:
Diagnosis and counselling - a number of patients have
been assisted merely by a diagnosis, which allows them to avoid the
condition/s that trigger an attack. After many years of living with
the condition they are relieved to have an explanation.
Surgery - surgery to repair the thinning of the bone has
been very successful. This surgery must be performed under a general
anaesthetic, and requires drilling through a section of the skull
above the ear, and using a cement to thicken the covering over the
superior canal. The problem is resolved for most patients, and
significantly reduced for others.
The Ear Science Institute Australia team is experienced in
providing assessment and advice on this condition. If you would like
to seek the advice of our specialist Audiologists please follow the
link below.
For more information see:
Banerjee A, Atlas MD, Whyte A (2004) Superior Canal Dehiscence (SCD): review of a new condition. Clinical Otolaryngology and Allied Sciences, accepted for publication.
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