POSTERIOR
SEMICIRCULAR CANAL OCCLUSION
Surgery
is usually reserved for cases that fail standard canalith repositioning
procedures. There are several
surgical options. Labyrinthectomy
of the affected ear can be quite effective for benign positional vertigo.
However, it seems to be too aggressive for the type of pathology
involved. Historically, singular
nerve section, was reportedly the treatment of choice.
However, few if any surgeons were able to accomplish this procedure
successfully without damaging vital hearing structures.
Transtympanic application of aminoglycosides (such as Gentamicin and
Streptomycin) is also an option. However,
like labyrinthectomy, it may be overkill.
Posterior
semicircular canal occlusion is the least destructive of the surgical options
for the treatment of benign positional vertigo.
Each
person has six semicircular canals (three on each side) and four linear
acceleration sensors. Labyrinthectomy
and transtympanic application of aminoglycosides destroys three of the
semicircular canals and two of the linear acceleration sensors.
In benign positional vertigo, only one semicircular canal is affected.
Semicircular canal occlusion treats only that one affected semicircular canal.
The
idea behind semicircular canal occlusion is based on the fact that the vertigo
is caused by movement of particles within the semicircular canal.
Crushing the canal would obviously immobilize these particles and thus
stop the vertigo.
Canal
occlusion is performed by working through a mastoidectomy approach.
The affected semicircular canal needs to be positively identified with
preoperative testing. The
identified canal is then surgically outlined with a fine diamond drill bit.
The membranes within the semicircular canal are delicately handled to
avoid complete fluid leakage. The
membranes are then crushed with muscle and autologous tissue grafting, trapping
and immobilizing the particles.
Posterior
semicircular canal occlusion is perhaps 95 percent effective in those who fail
standard canalith repositioning procedures.
The risks and complications include bleeding, infection, dizziness,
imbalance, facial nerve damage, hearing loss, tinnitus, and anesthetic
complications. Typically, patients
do fairly well in terms of vertigo control.
Sometimes they have little bit of residual imbalance because of the lack
of proper impulses from the abolished semicircular canal. This imbalance usually
improves with some balance re-training. There is perhaps a 5 to 10 percent
chance of a minor hearing loss. There
is typically less than 3 percent chance of total hearing loss in the affected
ear.
Sometimes
a course of vestibular rehabilitation is useful in compensating for the lack of
the abolished semicircular canal.
