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Vol. 66, No. 1 2015
Northeast Florida Medicine
Otolaryngology
The concept behind plugging of the dehiscence is to close
the “third” mobile window by filling the lumen of the bony
superior semicircular canal with bone wax and/or tissue.
The middle fossa craniotomy allows direct visualization
of the dehiscence from above. The transmastoid approach
to plugging involves creating two holes: one anterior and
one posterior, adjacent to the dehiscent area from the side
of the superior semicircular canal in order to wall off the
dehiscent area.
The concept behind resurfacing is to cover, or seal, the
defect without introducing material into the lumen of
the semicircular canal. As in plugging, there are the same
two approaches, middle fossa craniotomy (from above) or
transmastoid (from the side).
There are advantages and disadvantages to each strategy.
The advantage of plugging is complete closure of the bony
defect. Usually, the presenting symptoms and chief complaint
symptoms are resolved. The disadvantage of plugging is that
the membranous labyrinth is compressed and is potentially
irreversibly damaged, resulting in chronic disequilibrium of
a different nature
12-17
. The advantage of resurfacing is avoid-
ance of manipulation of the membranous labyrinth. The
disadvantage of resurfacing is the potential for incomplete
sealing of the defect, resulting in incomplete resolution of
presenting symptoms. The substance used for resurfacing
plays a large role in the sealing of the defect, avoidance of
potential trauma to themembranous labyrinth, and successful
resolution of symptoms.
Initial attempts at surgical management of a dehiscence
explored resurfacing versus plugging, both through amiddle
fossa craniotomy.This approach allowed direct visualization
of the dehiscence from above. In the early stages of surgical
management, a bone plate (with or without fascia) was used
to resurface the defect. Based on a limited number of cases,
this was found to be less successful than plugging, and was
abandoned early in the evolution of treatment in favor of
plugging.
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The most commonly used technique today is
the middle fossa craniotomy plugging of the dehiscence.
As experience has accumulated with plugging, either via
a middle fossa craniotomy or transmastoid approach, there
appears to be a tradeoff between the complete plugging of
the defect and the subsequent high incidence of chronic
disequilibrium due to loss of function of the superior semi-
circular canal. When a plug is pushed into the bony defect,
compression of themembranous labyrinth inevitably occurs,
with distention or rupture of the membranous labyrinth and
cupula.The result is dysfunction of the superior semicircular
canal cupula, with a different form of vestibulopathy. This
secondary morbidity has prompted a re-evaluation of resur-
facing, with the material used for resurfacing being a critical
factor. In retrospect, the unsatisfactory result fromthemiddle
fossa resurfacing was likely the result of the substance used
for resurfacing – the bone plate. Froma technical standpoint,
the bone of the floor of the middle fos sa around the area
of the dehiscence is irregular and undulating. Placement
of a rigid bone plate over this irregular bony surface of the
floor of the middle cranial fossa around the dehiscence is
not likely to provide a good seal of the dehiscence. An in-
complete sealing would not correct the pathological defect,
and therefore the symptoms would persist.
Retrospective analysis by various surgeons led to the
concept of using cartilage to resurface the defect.
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Cartilage
(from the auricle or tragus) is soft enough to conform to
the floor of the middle fossa around the defect and seal it,
and is firm enough to not prolapse into the lumen of the
semicircular canal. The cartilage cap accomplishes resur-
facing and sealing of the dehiscence without incidental
compression of the membranous labyrinth. Furthermore,
the cartilage cap is placed via a transmastoid approach,
therefore avoiding the need for a middle fossa craniotomy.
One potential disadvantage of placing the cartilage by a
transmastoid approach is the lack of visualization and di-
rect confirmation of the exact location of the dehiscence.
This potential disadvantage is overcome by intraoperative
confirmation of the bony labyrinth, use of highly accurate
intraoperative image guided navigational system, and use of
a piece of cartilage many times larger than the dehiscence. A
typical dehiscence is two to three mm long, and the cartilage
cap is at least 10 x 10 mm, more than adequate to cover the
defect and surrounding areas.
Operative morbidity is also a factor in recovery after sur-
gery. Typically, the middle fossa craniotomy with plugging
involves a three to five day hospitalization, including ICU
stay, with physical therapist necessary to assist in ambu-
lation. The postoperative course is also true of plugging
via a transmastoid approach. Either method of plugging
will result in compression and subsequent dysfunction of
the membranous superior semicircular canal and cupula.
The transmastoid cartilage cap resurfacing is done as an
outpatient in the vast majority of cases, and post-operative
morbidity is much less.
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Outcomes
As dizziness is such a vague symptom with multiple
etiologies, metrics for outcomes are difficult to establish.
Patient report, and provider interpretation of successful
outcomes and resolution of symptoms is often helpful, but
highly subjective and rarely provide a complete picture.
Most reports in the literature discuss patient report, such
as symptoms related to the dehiscence are resolved, or
symptoms are improved, etc. Audiograms can objectively
