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Endoscopic Assisted Middle Fossa Craniotomy for Resection of Vestibular Schwannoma
Brian S. Chen, MD; Daniel S. Roberts, MD, PhD; Gregory P. Lekovic, MD, PhD
House Clinic Los Angeles, CA
INTRODUCTION
CASE PRESENTATION
ABSTRACT
DISCUSSION
Introduction
Rates of hearing preservation following
vestibular schwannoma resection in
patients with lateral intracanalicular
locations are difficult. In this study we
present 2 cases who underwent
endoscopic assisted MFC resection of
intracanalicular vestibular
schwannomas with preserved
postoperative hearing.
Methods
Chart reviews were conducted on both
patients. Their presentation,
intraoperative details and techniques,
pre and postoperative audiograms and
facial functions are presented.
Results
Patient A had 5.6 x 6.8 x 13.2 mm
intracanalicular tumor with
unserviceable hearing (PTA 41, SDS of
47%, Class D) but was blind so
hearing preservation was
attempted. Postoperative hearing was
preserved (PTA 47, SDS of 60%, Class
B). Patient B had a 5mm round
intracanalicular tumor immediately
adjacent to the vestibule and cochlea
without any fundal fluid
present. Preoperative audiogram
showed serviceable hearing (PTA 48,
SDS 88%, Class B). Postoperative
audiogram showed minimal change
(PTA 51, SDS 76%, Class C) and
remained aidable. Gross total
resection was achieved in both
patients.
Conclusion
Hearing preservation surgery via MFC
can be enhanced with endoscopic
assisted dissection, especially in the
lateral IAC. The superior optical view
allows for preservation of cochlear
nerve function and removal of residual
tumors not otherwise seen on
microscopy. This is the first report of
endoscopic assisted dissection in the
IAC via MFC to our knowledge.
Patient A is a blind patient who had a 5.6 x 6.8 x 13.2 mm intracanalicular tumor
(Figure 1). His hearing was unserviceable (PTA 41, SDS of 47%, Class D) but due
to his blindness, hearing preservation surgery was attempted. Postoperative hearing
was preserved (PTA 47, SDS of 60%, Class B) (Figure 3). Although his facial nerve
was anatomically and electrically intact, he had delayed postoperative paralysis to a
grade 5.
Patient B had a 5 x 5 mm fundal tumor who opted for tumor resection in an attempt to
save hearing (Figure 2). His hearing was slightly diminished after surgery was but
still aidable (PTA 51, 76% SDS, Class C) (Figure 3). Postoperatively his face
remained a grade 1.
Rates of hearing preservation following vestibular schwannoma (VS) resection via
middle fossa craniotomy (MFC) in patients harboring tumors with unfavorable
characteristics are significantly lower than for patients with ‘favorable’ tumors.
Unfavorable characteristics include non-serviceable preoperative hearing or tumors
extending in the lateral internal auditory canal (IAC) without evidence of fundal fluid.
A limitation of the MFC is visualization of the most lateral extent of tumors impacted
into the fundus of the internal auditory canal (IAC). Residual tumors can hide under
the ledge of bone at the distal IAC which is not visualize by the microscope’s line of
sight. Furthermore, drilling near the fundus is limited due to the proximity of the
cochlea anteriorly and superior canal posteriorly. Blind dissection is often taken to
remove tumors in this location. In these cases, endoscopic assistance can be of
benefit because it allows the surgeon to fully visualize the fundus and achieve a
gross total resection without inadvertent injury to the cochlear or facial nerve.
In this study we present 2 cases with unfavorable conditions, who underwent
endoscopic assisted MFC resection of intracanalicular vestibular schwannomas and
achieved gross total resection with preserved postoperative hearing.
In the English literature, the majority of endoscopic assisted VS resections are
published for the retrosigmoid (RS) approach. For this approach, the endoscope
allows surgeons to not dissect blindly, which has often been the biggest
disadvantage to the RS approach when tumors involve the lateral IAC. These two
cases show the clear visual advantage of the endoscope for dissecting in the lateral
IAC in MFC approaches.
One criticism of this technique is the potential risk of inadvertent direct injury to
nearby structures with the endoscope itself when advancing it into position. This is
especially true when trying to navigate an angled scope strictly using the endoscopic
display. In order to minimize this, we advance the endoscope under direct
visualization of the microscope. Once we are satisfied with the location of the
endoscope by checking our view with both the microscope and the endoscopic
display, the surgeon transitions attention to the endoscopic display for tumor
resection, and the assistant maintains observation of the endoscope tip. The bulk of
our tumor resection is still made under the microscope. Endoscopic assistance is
only used when we suspect, or cannot confirm, residual disease in the lateral canal.
Another potential pitfall of endoscopic resection is the heat produced by the light
source of the endoscope which can potentially damaging blood vessels (AICA) and
nerves (Facial nerve) that are in direct view. We postulate that this in fact may have
contributed to facial weakness observed in patient A. The risk of facial nerve injury
can be minimized by reducing the light source intensity (similar to that done for
middle ear endoscopy) along with frequent irrigation, either manually with a syringe
or with an Endoscrub (Medtronic: Minneapolis, MN, USA).
Figure 3. Pre- and Postoperative Audiograms for Patient A and B. Patient A’s hearing improved from Class D
(PTA 41, 48%SDS) preoperatively, to a Class B (PTA 47, 60%SDS) postoperatively. Patient B’s hearing slightly
worsened from a Class B (PTA is 48, 88%SDS) to a Class C (PTA is 51 ,76%SDS) which was still aidable.
Figure 4. Case A: Tumor dissection in the lateral IAC is conducted with the endoscope but is also under direct
view of the microscope in order to not inadvertently injury surrounding structures. A. Notice the blind dissection
that occurs under microscopy when the Mcelveen-Hitselberger Neural Dissector is placed into the IAC to remove
residual tumor. B. On endoscopy, however, the facial and cochlear nerves are visualized so the end of the nerve
dissector is not dissecting blindly, preventing unnecessary facial paresis and hearing loss.
Figure 1. Preoperative MRI for patient A. A. T1 weighted MRI with contrast shows a right IAC lesion (white arrow)
spanning from the porus to the lateral IAC. B. T2 weighted MRI shows a filling defect (white arrowhead) in the
IAC with minimal fundal fluid (white arrow).
Figure 2. Preoperative MRI for patient B. A. T1 weighted MRI with contrast shows a left sided lateral IAC
hyperintense lesion at the fundus (white arrow). B. T2 weighted MRI shows a filling defect in the lateral IAC and
absence of fundal fluid lateral to the tumor (white arrow).
Figure 5. Case A: After tumor resection with
endoscopic assistance in the lateral fundus,
there is no residual tumor. With a 30 degree
endoscope, the facial nerve (FN) is depicted all
the way to the fundus and the transverse crest
(arrow) can also be seen.
MICROSURGICAL RESECTION
After microscopic resection, micro-cottonoids are placed over the temporal lobe dura
to prevent inadvertent injury. A surgical endoscope (3mm x 14cm Hopkins Rod,
Storz: Tuttlingen, Germany) is brought into the operative field under direct
visualization of the microscope. 0, 30 and 70 degree endoscopes are used as
dictated by the field of view. Using conventional micro-instruments and micro-
dissection techniques, the residual tumor is removed from the fundus of the IAC
(Figure 4). After tumor removal, the fundus is inspected for residual tumor (Figure 5).
Correspondence information: Gregory P. Lekovic, MD, PhD
Neurosurgical Associates of the House
Clinic
2100 West 3rd Street, Suite 111
Los Angeles, CA 90057
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microsurgery for removal of vestibular schwannomas. J Neurol Surg B
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2. Kumon Y, Kohno S, Ohue S, et al. Usefulness of endoscope-assisted
microsurgery for removal of vestibular schwannomas. J Neurol Surg B
Skull Base. 2012;73:42-47.
3. Kumon Y, Kohno S, Ohue S, et al. Usefulness of endoscope-assisted
microsurgery for removal of vestibular schwannomas. J Neurol Surg B
Skull Base. 2012;73:42-47.
4. Goddard JC, Schwartz MS, Friedman RA. Fundal fluid as a predictor of
hearing preservation in the middle cranial fossa approach for vestibular
schwannoma. Otol Neurotol. 2010;31:1128-1134.
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6. Kumon Y, Kohno S, Ohue S, et al. Usefulness of endoscope-assisted
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