Rapid, uncontrollable eye movements that swish and
thump as the eyes roll and blink. Bones that creak as the
body moves. Sudden dizziness, loss of balance. Falling down
after a loud noise, such as the sound of your own voice, a
cough or even laughter. These are hallmarks of a
debilitating and relatively rare syndrome known as superior
canal dehiscence that has stumped clinicians for a long
Victims lose balance, fall down stairs, or are unable
to read or sleep due to loud noises inside their head, and
some become convinced they are mentally ill, suffering from
symptoms that won't yield to conventional treatment. Now,
Johns Hopkins surgeons have proved that these symptoms can
all be successfully treated by a single operation that
plugs up a threadbare layer of bone in the inner ear.
Superior canal dehiscence occurs in roughly equal
numbers of men and women and is often not diagnosed until
after age 40, when symptoms, such as hearing loss, appear
to worsen. However, patients often recall that initial
symptoms happened much earlier in their lives.
"The surgical plugging procedure can put a stop to
even severe symptoms and can lead to a return to normal
daily activities and, in some cases, to a mild to moderate
improvement in hearing," said Lloyd B. Minor, the Andelot
Professor and director of
Otolaryngology-Head and Neck Surgery at the Johns
Hopkins School of Medicine. It was Minor who, in 1998,
first clinically described superior canal dehiscence and
developed the surgical techniques to repair it.
In a pair of reports believed to offer the largest
follow-up analysis of patients after their surgery for the
syndrome, a Johns Hopkins team, led by Minor, found that
plugging the superior canal where the bone casing is thin,
and then covering the plug with a bone graft, prevented
symptoms from recurring.
Researchers say that for patients who had already
experienced some hearing loss from the syndrome, the
plugging procedure — which essentially compresses and
closes off the canal — often helps restore their
hearing. They note that improvements in hearing occurred in
five of 29 patients who underwent surgery for the disorder
between 1996 and 2005.
They add that the risk of hearing loss is very low in
patients who have not had previous ear surgery, with no
hearing loss reported in 19 patients undergoing their first
No wider than a toothpick, the canal bone in question
rests at the top of the inner ear's three semicircular
canals. Thinning due to failure of bone to develop properly
and maintain its strength over time makes the ear
hypersensitive to sound and motion. A common complaint is
autophony, where patients hear their own voices
reverberating inside their head. For some patients, even a
conversational level of loudness can produce symptoms
strong enough to cause severe discomfort.
The Johns Hopkins surgeons presented their findings
from a decade's worth of research on May 20 at the Combined
Otolaryngological Spring Meeting being held in Chicago.
Since the team saw its first patient with the condition in
1995, it has successfully operated on 39.
While no survey exists of just how widespread the
condition is, Minor says that about two-thirds of those who
have it will never require surgery. But for the remaining
one-third who undergo surgery to repair the bone casing in
the ear, the surgery in most cases fixes the disturbance in
balance caused by the dehiscence.
In their latest findings, researchers report that in
19 patients undergoing analysis of abnormal eye movements,
surgery led to a resolution in each case of vertigo, or
dizziness, brought on by loud noises.
The surgery, which takes from four to six hours, is
extremely delicate and requires access to the inner ear, a
space the surgeons describe as no wider than the diameter
of a dime. They first cut a hole above the ear and open the
skull, after which they move aside a part of the brain so
that they can reach the three paired canals that form the
inner ear, of which the superior canal is the one closest
to the top of the head. The plug mixture is made up of
small chips of the patient's bone and fibrous tissue taken
from the area of incision and the temporary opening the
surgeons make in the skull.
In the first study presented at the COSM, audiograms
were performed both pre- and postsurgery to assess hearing
levels. In the second study, tests of eye movements in
response to sound and to rapid head movements were used to
assess the inner ear's balance function after surgery.
Minor cautions that the surgery has the potential to
damage balance but notes that the studies suggest the other
two balance canals, the posterior and horizontal canals,
can adapt. Postsurgery results showed a 44 percent
reduction in the function of the superior semicircular
canal, while function in the other two canals was typically
not affected. This shows, researchers say, that plugging
typically limits sensation in just the one canal.
The results should allow surgeons to better counsel
their patients with superior canal dehiscence on what is
the likely improvement to their hearing and balance after
either procedure, according to the lead authors of the
studies, John Carey, an associate professor, and Charles
Limb, an assistant professor, both in Otolaryngology-Head
and Neck Surgery.
However, Limb notes that only long-term data from
postsurgical monitoring of patients for longer than 10
years will truly confirm if surgical treatments hold steady
or decline at some point. The Johns Hopkins team continues
to monitor how its patients are doing.
Although research on the condition is relatively new,
Minor believes the underlying cause of the syndrome is an
opening in a layer of bone that fails to develop to normal
thickness during or after birth. The open balance canal can
then respond to sounds and to pressure induced by
activities such as coughing, sneezing or straining. This
abnormal activation of the canal is then misinterpreted by
the brain as a head movement that leads patients to lose
their balance and to have abnormal eye movements.
According to Minor, normal inner ear bone thickness is
on average 0.7 millimeters. And while the condition can
affect both ears, in patients with just one ear affected,
the other ear has less than normal bone thickness.
Diagnosing the condition consists of CT scans of the
head to gauge the thickness of the bones in the inner ear,
as well as balance tests to record how various sounds
trigger body motions, including eye movements and
contractions of muscles in the neck.
Funding for this study was provided in part by the
National Institute on Deafness and Other Communication
Disorders, a member of the National Institutes of
In addition to Minor, Carey and Limb, other
researchers involved in this research, conducted solely at
Hopkins, were Americo Migliaccio and Sharmila Srireddy.