38
it would be a viable option for the removal of
acoustic neuromas [ 2 ]. Through this approach, the
entirety of the contents of the internal auditory
canal (IAC) can be visualized, and the facial nerve
can be positively identified in the fallopian canal
without tumor involvement [ 3 , 5 ]. While initially
used to remove tumors of all sizes, through Dr.
House’s first ten clinical cases as well the observa-
tions of John B. Doyle, Jr., it was realized that in all
but the smallest of tumors a labyrinthectomy was
required to gain the appropriate access to the cere-
bellopontine angle (CPA) [ 6 ]. It was also noted to
be a technically challenging operation as the expo-
sure is limited, there is a lack of definitive land-
marks, and the facial nerve is often submitted to
more manipulation than in other approaches [ 7 , 8 ].
Limitations in early detection of acoustic neuromas
at the time led to relatively infrequent use of the
middle fossa approach; however, House and
Hitselberger did determine through their series of
patients that hearing and facial nerve function
could be preserved if tumors were small [ 9 ]. With
the eventual development of gadolinium-enhanced
magnetic resonance imaging (MRI), there was an
increased identification of patients with small
tumors and serviceable hearing [ 3 ]. Consequently,
an approach that could preserve hearing became
desirable, leading to more widespread adoption of
the technique. The middle fossa approach has been
utilized for repair of superior semicircular canal
dehiscence, encephaloceles, access to the petrous
apex, decompression of the facial nerve for Bell’s
palsy or trauma, and other IAC lesions [ 1 – 13 ].
Prior to the technological advances that made the
middle fossa approach more feasible, House and
Hitselberger also developed the translabyrinthine
approach, which gave a direct route to the CPA
through the temporal bone [ 14 , 15 ]. While hearing
is sacrificed because the vestibular portion of the
inner ear is obliterated, this approach provides
wide exposure with potential identification of the
facial nerve from the brainstem to the stylomastoid
foramen. The CPA and IAC are also widely
exposed via translabyrinthine exposure. The
approach is primarily extradural, and there is mini-
mal to no brain retraction. Due to the wide expo-
sure, the translabyrinthine approach is also used for
facial nerve decompression when hearing does not
need to be preserved, facial nerve repair and the
removal of other CPA lesions, including meningio-
mas, intracranial epidermoids, and paragangliomas
[ 16 ]. As compared to the classic suboccipital
approach, the patient is in the supine position (ver-
sus sitting), which reduces the risk of air embolism
as well as the rare but serious complication of spi-
nal cord infarction and quadriplegia [ 17 ]. The
translabyrinthine approach has also been found by
some authors to have a lower incidence of postop-
erative CSF leak and headache as compared to the
retrosigmoid approach, while others have found
the rate of CSF leaks to be similar [ 18 , 19 ].Preoperative Evaluation
Patients with an acoustic neuroma most often
present with complaints of unilateral hearing
loss, followed by tinnitus, vertigo, and, rarely,
facial hypesthesia in descending order [ 20 ]. Once
a complete clinical history and physical exam
have been performed, pure-tone and speech audi-
ometry are important diagnostic tests to perform.
The auditory brainstem response (ABR) was
long considered the most sensitive diagnostic
modality, with the interaural wave V latency
being greater than 0.2 ms considered abnormal
[ 21 ]. However, the use of enhanced MRI has
found the false negative rate of ABR to be
18-30% for intracanalicular tumors [ 22 ]. We do
not routinely perform ABR to screen for acoustic
neuromas at our institution because of the limited
clinical utility. If sufficient clinical suspicion
exists based on symptoms and audiometry, the
imaging modality of choice is a gadolinium-
enhanced MRI. As an alternative to using
contrast- enhanced MRI, a screening protocol
with a fast spin-echo MRI sequence is highly
sensitive and specific and provides ultrahigh-
resolution images of the IAC, making it possible
to determine the nerve of origin of very small
tumors [ 23 ]. We found there was no difference in
diagnostic accuracy compared to traditionally
enhanced sequences and that the diagnostic accu-
racy is more sensitive and specific than brainstem
audiometry (ABR) at a similar cost and is signifi-
cantly cheaper than contrasted MRI [ 23 , 24 ].J.C. Sowder et al.