INTRODUCTION
The most common
Cerebellopontine angle (CPA) tumour is schwannomas, followed by meningiomas,
and epidermoid cysts. The other tumours are rare1. Non-tumorous
pathologies are trigeminal neuralgia (TN), hemifacial spasm (HFS), and
glossopharyngeal neuralgia2. Clinically,
CPA lesions may present with cranial nerves dysfunction, cerebellar and/or
brainstem compression, raised intracranial pressure (ICP), and /or localized or
non-localizing headache3. Magnetic resonance imaging (MRI) is
the first method for diagnosis of CPA tumors. Computerized Tomography (CT) is
more useful for bony structures evaluation and for the description of the
relation of the tumour to internal auditory canal (IAC)1. The goals
of treatment of CPA lesions are avoiding mortality, preventing progressive
neurological disability, minimizing treatment complications, and maintaining
regional cranial nerve function4. Endoscopic procedures of the CPA
provide increased visualization of the CPA without retractors, identification of neurovascular structures ensuring
surgical success with less postoperative morbidity and
decreased length of stay5. For MVD, it provides a more comprehensive
evaluation of the completeness of microvascular decompression (MVD)6.
Insertion of the endoscope in CPA should be preferably done under control of
operating microscope7. The endoscope has
some disadvantages as unavailable instrumentation designed specifically for
endoscopy of CPA, potential thermal injury and lack of three dimensional (3D)
vision8. The aim
of this work is the assessment of the effectiveness, safety, and advantages of
the use of endoscope during microsurgical management of CPA pathologies.
PATIENTS
AND METHODS
This
is a prospective descriptive
clinical study of 25 patients diagnosed as having CPA pathology. The
data were collected from the department of neurosurgery, Suez Canal University
Hospital, Ismailia, Egypt,
from January 2008 to August 2010. The patients were subjected to neurological
examination, facial nerve VII function grading (House-Brackmann (HB) grades9),
pure tone audiometry and speech discrimination score according to Gardner and Robertson’s
classification as grades from I to V10. Patients were investigated
by CT and MRI without and with contrast.
Tumors in the CPA were categorized as small (<15 mm3),
medium (15–30 mm3), large (30-40 mm3), and giant (>40
mm3)11,12. Tumor extension was evaluated according to Hannover classification (Table 1)13.
Endoscopic Instruments: rigid endoscopes (Hopkins)
telescope 4 mm diameter, 18 cm
length, 0 and 30 degrees, irrigation systems, endoscope holding arm, light
source, Coupled Charged Device (CCD) camera, monitor, and video recorder.
All patients were managed using a standard microscopic retrosigmoid approach. For MVD a small Teflon patch was used. First endoscopic
survey: The endoscope was introduced into the CPA under
microscopic guidance aiming at observation of the CPA contents and tumor
borders, here it is considered beneficial. Second endoscopic survey: aimed
at confirmation of total tumor excision, full MVD, closure of opened air cells
at the IAC, and report of cerebellar contusion.
It is then considered beneficial. Assessment of Outcome: For TN and HFS:
Clinical improvement was categorized according to Barrow Neurological Institute
for pain intensity score (Table 2)14. Postoperative MRI was done.
Postoperative complications were reported.
Table 1.
Hannover Classification of cerebellopontine angle
vestibular schwannoma extension.13
Grade
|
Tumor extension
|
T1
|
Tumor is purely
intrameatal
|
T2
|
Tumor is
intra-and extra-meatal
|
T3a
|
Tumor is filling the cerebellopontine angle cistern
|
T3b
|
Tumor is reaching
the brain stem
|
T4a
|
Tumor is compressing
the brain stem
|
T4b
|
Tumor is severely
dislocating the brain stem and the fourth ventricle
|
Table 2. Barrow
Neurological Institute pain intensity score after MVD for TN.14
Score
|
Pain relief
|
I
|
No pain, off
medications
|
II
|
Occasional pain,
off medications
|
IIIa
|
No pain,
continued use of medications
|
IIIb
|
Pain persists,
but adequately controlled with medications
|
IV
|
Pain not
adequately controlled with medications
|
V
|
No relief
|
RESULTS
Patients age ranged
from 21 to 61 years with a mean/SD of 45±11.02 years. There were 12 (48%) males
and 13 (52%) females. There were a 12 patients with
VS, 4 patients with meningiomas, 3 patients with epidermoid, 3 patients with
TN, and one patient with each of arachnoid cyst, metastasis, and HFS. The
duration of symptoms ranged from 2 months to 30 months with a mean/SD of
10.2±8.59 months. Headache was the most frequent symptom in 40%. Sensory Neural Hearing loss (SNHL) was present in 44%of
patients, facial paralysis in 16%, facial hyposthesia in 20%, and lower cranial
nerve affection in 8%. Hydrocephalus in 12% and managed by ventriculoperitoneal
shunt. Regarding the 12 patient with VS, seven tumors were giant, four
were large, and one was medium. According to the Hannover grading, five tumors
were grade T3b, another five were T4a, one was T3a, and another one was T4b.
Eight patients had widening of the IAC, four had cystic changes in their
tumors, and all the patients showed enhancement of their tumors after injection
of gadolinium contrast either homogenously in seven or heterogeneously in five.
Four patients with meningiomas, two were medial to
the IAC, one lateral to it, and one superior to it. One meningioma was medium
sized, two were large and one was giant tumor. In patients with TN, no
abnormalities were detected in MRI, while in HFS, MRI
and MRA revealed the basilar artery compressing VII nerve. First survey was completed in 84% and aborted in 16%. It was beneficial
in 80%. Second survey was tried in all
patients except one and was beneficial in 96%. Tumor debulking before
endoscopic insertion was needed in 81%. The VII and Vestibulocochlear (VIII)
nerves were endoscopically visible in first survey in 64% and 48% respectively.
In patients with VSs, the VII nerve was visible in only 41.7%. During
second endoscopic survey: the VII and VIII nerves
were anatomically intact in 92% and 80% respectively. There were 24% 0f
patients in whom opened air cells were seen only with the endoscope and in 16%
residual tumors were present and seen with the endoscope (Figure 1). The time added by endoscope ranged from 15 to
45 minutes with a mean and SD of 29.4±8.3 minutes. The mean operative time
added by endoscope increased with increasing tumor size in schwannomas. Complication: The overall
complication occurred in 36% (9 of 25) of patients, but most of it was simple
and recoverable. Two complications were related to
the endoscope (8%); increased VII nerve weakness and cerebellar ataxia. Outcome of the Study: The
endoscopic view of completeness of tumor removal was the same as the
radiological outcome immediate postoperative. Total tumor removal achieved 17
and incomplete removal in three. There was one case of recurrence in a patient
with meningioma. Cranial nerve outcome: Postoperatively in the 25
patients, six had increased facial weakness, after one year follow up, five of
them improved and one remained the same. Four patients showed increased hearing
deficits postoperatively and not improved. Outcome in TN (Figure 2). There were
3 patients presented with TN, two of them were improved completely and became
free of medications (grade I) and one patient improved but still in need for
some medications (grade II). Patient with HFS: The compressing vessel was a
tortuous basilar artery, Teflon patch inserted properly with both the endoscope
and microscope.
Figure 1. Vestibular schwannoma before (left) and after (right)
total endoscopic excision with the facial nerve intact.
Figure 2. Endoscopic MVD for TN, before (left) and after
(right) Teflon insertion by the endoscope.
DISCUSSION
By
identifying anatomic windows, the endoscope allows us to perform surgery
through smaller exposures, with less brain retraction15. The
duration of symptoms in our series ranged from 2 months to 30 months. Ewa et al.
reported a clinical history ranged from 3 months to 22 years, with average
duration of symptoms was about three years1.
This is the case in other different studies discussing the clinical
presentation of VSs with some difference in figures due to difference in tumor
size or patient’s number16,17. Regarding TN and in contrast to our
results, Aryan fount that in a 19 patients with TN, in high resolution thin
cuts MRI, the compressing vessel seen by in 17 patients18. In another series by Fukuda et al, MRA correctly identified
offending vessels in 14 (67%) of the 21 TN and 34 (87%) of the 39 HFS patients19.
This difference in detecting the compressing vessel can be explained by the
usage of MRI brain in our patients while the others using MRI posterior fossa.
Regarding the 12
patients with VSs, seven of them have giant VSs. Our results regarding the size
of the tumor differ from that in the literature as our patients usually
presents lately than reported in other series, in addition to the smaller
number of patients. In the large series
of Matthies and Samii in 1000 of patients, tumor extension analysis showed that
3% of tumors belonged to Class T1, 17% to Class T2, 44% to Class T3, and 36% to
Class T420. Gormley et al in a series of 179 VSs found that, 37% of
the tumors were small, 47% as medium, and 16% as large21. Park et al
found that, the most common type of VS was mixed solid and cystic nature in 26
patients (52%), followed by solid form in 20 (40%) and totally cystic form in
only 4 (8%)22. The incidence of the cystic variety depends on the
percentage of large tumours making up the series23. Voss et al in 40
patients with CPA meningiomas found the most common site of dural origin to be
anterior to the IAC in 26%, posterior 21%, superior 18%, and inferior 16%24. Operative data: Wackym et al found
that; in 19 of 68 patients (28%) exposed air cells were not seen with the
microscope during retrosigmoid approaches but were identified endoscopically25.
Gerganov et al. used the endoscope in large VSs and found that an initial tumor
debulking to be performed28. During endoscope-assisted MVD for TN,
gentle retraction of the cerebellum, release of CSF from the basal cisterns,
and lyses of the arachnoid bands was the role in all cases in the series of Teo
et al and others6,26,27.
These results matched with our results but our results are less promising due
to our early experience with the endoscope, larger size of tumors and
unavailability of cranial nerve monitoring. The VII & VIII nerves were
clearly visible with the endoscope during first survey in all patients with
epidermoid cyst, arachnoid cyst, TN, and HFS. They were visible in 75% of the
patients with meningiomas, and in 41.7% for the VII nerve and in 8.3% for the
VIII nerve. The VII & VIII were anatomically intact in 92% and 80% during second
survey respectively. There were six patients (24%) in who opened air cells were
seen only with the endoscope. There were five patients (20%) in whom residual
tumors were detected only with the endoscope. Kabil and Shahinian in a series
of 112 fully endoscopic resections of VSs found anatomical preservation of the
facial nerve in all of the patients and of the cochlear nerve in 83/101 (82%)
of hearing ears10. Similar findings were reported by Hori et al.29
and Moriyama et al.30 and Gerganov et al.28. These
results are matched with our results with some differences due to learning up
curve of endoscopic assisted surgery and the radiological characters of the
lesions in our series. In patients with TN operated microscopically, Li et al.
reported that, complete MVD was achieved in 80.6%31 where as when
done endoscopically a more than 95% achievement in Teo et al.27. In
our study, the operative time added by endoscope ranged from 15 to 45 minutes.
Previous studies mentioned that, endoscopic procedures added an average time of
15 to 30 minutes to the duration of surgery during endoscopic assisted MVD or
large VSs6,25,28, 32 . Completeness of tumor excision: Of the 21 patients with mass
lesions, complete removal achieved in 18 (85.7%). Wackym et al. reported
more than 96% success of complete tumor excision25. In a series of
178 VSs found that, only one patient (0.6%) underwent an incomplete tumor
resection21, and similar figures were reported by Gerganov et al33.
These results are matched with our study and both document the benefit of the
endoscope in achieving complete tumor excision. Tumor remnant after total
microsurgical removal are detected by the endoscope in 0 – 17.6% in different
series25,34. Most of previous studies
document the importance of endoscope in reducing the need for cerebellar
retraction and CSF release to totally remove the tumors32,35. In agreement to previous studies, there were
no added facial or auditory deficits in our patients with TN, HFS, and
arachnoid cysts. In the patient with medium sized VS, no hearing or facial
weakness complicate the course of the patient. As the VSs increase in size,
more injury to the VII and VIII nerves occurred. Göksu et al in a series
of 32 VSs found that postoperatively, six patients suffered from grade II
facial weakness, 2 from grade III, and one from grade IV, with all other
patients having grade I facial function34. In 32 patients Hori et al. achieved anatomical preservation of the
facial nerve in 31 cases, and damage of the facial nerve by the endoscope was
met once7. Overall these findings are more or less similar to our
findings but comparison with those of larger series is difficult because there
are no uniform criteria for categorizing surgical results and we have no
cranial nerve monitoring during CPA surgeries. Outcome in TN: In our three patients complaining of TN,
two were improved completely and became free of medications (grade I) and one
patient improved but still in need for some medications (grade II). Similar
results were reported by Kabil et al 37 and Ramin et al38.
Our number of patients is not comparable to these series. Complication: Nine patients
(36%) have a complicated postoperative course. Wackym et al. reported
negligible complications in 2 of their series25. In 1.177 cases of
endoscope assisted minimally invasive retrosigmoid approach, the most common
complication was CSF leakage, encountered in 3.6% cases36. Other
series6,32,37 reported equal figures of complications. In our study
there was a slight trend suggesting more frequent CSF leak with cases of larger
tumors, but the number is small for a definitive statistical conclusion. Two complications were related to the endoscope (8%). There
were no complications related to the use of the endoscopy in many previous
studies6,25,38. Recurrence: There was one case of recurrence
in a patient with meningioma. Yuguang et al in a series of 28 endoscopic
assisted CPA surgeries reported that, no recurrences in patients with tumors,
and all TN patients cured32. Accurate
comparison with other studies is difficult due to differences in follow up
periods and number of the patients. We have no mortality in our study which is
the result also in most of other endoscopic studies6,26,27. In a
comparative study between the endoscopic and microscopic MVD, the mortality
rate was zero for endoscopic group and ranged from zero to 1.4% in microscopic
group37. We followed our patients from a
minimum of 2 months to a maximum of 30 months.
This period is short as more recurrence can appear at a delayed times. Cheng
et al in a 32 patients underwent endoscope-assisted MVD or fully endoscopic MVD
for HFS, the procedure was successful in 96.9%36.
Conclusion
Endoscopic assisted
microsurgery for treatment of CPA pathologies is effective and safe procedure
that provide increased visualization without retractors, ensuring surgical
success with less postoperative morbidity. Some
benefits of endoscope use in the CPA have been revealed, as better control of
total tumor excision, decrease the cranial nerve injuries, and improved visualization, identification of neurovascular
structures, and extensive drilling of the posterior portion of the IAC.
[Disclosure: Authors
report no conflict of interest]
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