Keywords
hemilaminectomy - Spinal schwannomas - spinal intradural extramedullary tumors - spinal
minimally invasive approaches - laminectomy
Introduction
Spinal schwannomas are benign slow-growing tumors, and gross total resection is the
gold standard of treatment. The conventional surgical approach is laminectomy, which
provides a wide working area. However, minimally invasive approaches, such as hemilaminectomy,
minimize tissue traumas and avoid spinal instability, but they may be relatively contraindicated
in large spinal tumors.[1]
[2] Because of the weak adherence of a spinal schwannoma tumor to surrounding tissues,
excision via a hemilaminectomy appears feasible. In this article, we describe and
discuss our experience and results about a series of patients with spinal schwannoma
and operated on with laminectomy or hemilaminectomy.
Material and Methods
From January 2016 to December 2019, we operated 40 patients with a spinal intradural
schwannoma via laminectomy or hemilaminectomy. In all cases, surgery was indicated
for the treatment of the symptoms (neurologic deficit, intractable pain, numbness)
and the diagnosis was obtained by contrast-enhanced magnetic resonance imaging (MRI).
In the last 18 months of the study, spinal schwannoma was treated exclusively via
hemilaminectomy[3]; only very large schwannomas were treated via laminectomy.
Baseline medical data, including patients' sex, age, tumor location and volume, overall
operative time, length of postoperative immobilization, duration of hospitalization,
1-month post-op visual analog scale (VAS) value comorbidities, and preoperative American
Society of Anesthesiologists (ASA) physical status classification system were collected
and analyzed ([Table 1]). Tumor size was measured using the widest diameter in three planes and the volume
was calculated (ellipsoid method volume = D1 × D2 × D3/2). The diagnosis of schwannoma
was confirmed in all cases at histopathology. All procedures were performed by two
expert neurosurgeons.
Table 1
Baseline characteristics of patients
|
Laminectomy (n = 27)
|
hemilaminectomy (n = 13)
|
p value
|
|
Age (y)
|
66.2 (13.4)
|
60.0 (9.7)
|
0.144[a]
|
|
Male sex
|
7 (25.9)
|
1 (7.7)
|
0.177[b]
|
|
Site of surgery
|
|
Cervical
|
3 (11.1)
|
5 (38.5)
|
0.105[b]
|
|
Thoracic
|
18 (66.7)
|
5 (38.5)
|
|
Lumbar
|
6 (22.2)
|
3 (23.0)
|
|
Tumor size (ccm)
|
0.61 [0.35–0.85]
|
0.60 [0.45–0.80]
|
0.675[c]
|
|
Baseline ASA status
|
2.1 (0.7)
|
2.2 (0.6)
|
0.980[a]
|
Abbreviation: ASA, American Society of Anesthesiologists physical status classification
system.
Note: Data are mean (SD) for continuous variables, and n (%) for categorical variables.
a Two-sample t-test.
b Chi-squared test.
c Mann-Whitney test.
Operative Technique
The patient was placed in the prone position under general anesthesia. A midline skin
incision was centered on the radiograph marker positioned in the spinous process over
the tumor. Intraoperative neurophysiologic monitoring was not used, in 5 out of 40
cases. In hemilaminectomy, the paravertebral muscles of the tumor side were retained
to reach the hemilaminae. By means of a high-speed pneumatic drill or piezoelectric
device, the hemilaminae were removed to expose the dural sac. In some patients with
more lateral tumor, the exposure was completed with a partial facetectomy. The dural
sac was opened under operating microscope magnification and the tumor was decompressed
internally by the cavitron ultrasonic aspirator. Finally, the capsula was dissected
from the surrounding tissues in the majority of cases; when this was not possible,
for dorsal schwannomas, the sensitive nerve root was coagulated and cut, whereas for
cervical and lumbar tumors, a small tumor residual near the nerve was sometimes left
([Fig. 1]). The dura mater was sutured in a watertight fashion with 4–0 silk wire. Fibrin
glue and fat were applied epidurally to reinforce the closure. In case of laminectomy,
the muscle dissection was bilateral, the laminae were removed, and the dural sac was
exposed and opened for tumor removal under the operating microscope ([Fig. 2]). Instrumentation for spinal instability was never required.
Fig. 1 (a) Preoperative cervical magnetic resonance imaging (MRI) study. (b) Intraoperative unilateral hemilaminectomy with tumor exposure. (c) Postoperative computed tomography (CT) scan study.
Fig. 2 (a) Preoperative dorsal magnetic resonance imaging (MRI) study. (b) Intraoperative laminectomy with tumor exposure. (c) Postoperative computed tomography (CT) scan study.
Statistical Analysis
Values are presented as mean ± standard deviation (SD) or median (interquartile range
[IQR]) for continuous variables and as the number (percent) of subjects for categorical
variables. Univariate comparisons were made through Student's t-test, Mann–Whitney test, or chi-squared test, as appropriate ([Table 2]). The association between the VAS score at follow-up and the type of surgery (laminectomy
vs. hemilaminectomy) was estimated using a linear regression analysis ([Table 3]). Age, sex, operative time, tumors size in cubic centimeter (ccm) and level of surgery
were included in the multivariate models. Results were considered significant for
p values <0.05 (two sided). Data analysis was performed using STATA/IC 13.1 statistical
package (StataCorp LP, College Station, Texas, United States).
Table 2
Operative outcomes according to surgical intervention type
|
Laminectomy (n = 27)
|
Hemilaminectomy (n = 13)
|
p value
|
|
Operative time (min)
|
160 [130–240]
|
90 [80–100]
|
<0.001[a]
|
|
Time spent in bed (h)
|
72 [70–100]
|
48 [24–70]
|
<0.001[a]
|
|
Hospitalization length (d)
|
12 [10–15]
|
7 [5–9]
|
<0.001[a]
|
|
Follow-up VAS score
|
4.6 (1.7)
|
2.5 (1.3)
|
<0.001[b]
|
Abbreviation: VAS, visual analog scale.
Note: Data are mean (standard deviation [SD]) or median (interquartile range [IQR])
for continuous variables, and n (%) for categorical variables.
a Mann–Whitney test.
b Two-sample t-test.
Table 3
Linear regression model predicting visual analog scale score at follow-up
|
Variable
|
Unadjusted
|
Adjusted[a]
|
|
β coefficient (95% CI)
|
p value
|
β coefficient (95% CI)
|
p value
|
|
Age
|
0.01 (–0.04 to 0.06)
|
0.591
|
0.01 (–0.04 to 0.06)
|
0.689
|
|
Sex
|
0.79 (–0.60 to 2.18)
|
0.258
|
0.43 (–1.16 to 2.01)
|
0.588
|
|
Tumor size
|
–0.01 (–1.53 to 1.51)
|
0.994
|
0.07 (–1.30 to 1.44)
|
0.920
|
|
Baseline ASA status
|
0.56 (–0.33 to 1.45)
|
0.210
|
0.57 (–0.50 to 1.63)
|
0.285
|
|
Operative time
|
0.009 (–0.003 to 0.016)
|
0.007
|
0.003 (–0.005 to 0.012)
|
0.399
|
|
Site of surgery
|
0.54 (–0.36 to 1.43)
|
0.234
|
0.37 (–0.50 to 1.23)
|
0.391
|
|
Type of surgery
|
–2.02 (–3.10 to –0.93)
|
0.001
|
–1.47 (–2.91 to –0.04)
|
0.044
|
Abbreviations: ASA, American Society of Anesthesiologists physical status classification
system; CI, confidence interval.
Note: β coefficients with their 95% CIs and corresponding p values from linear regression models are shown.
a Adjusted for age, sex, operative time, site, and type of surgery.
Results
In total, 40 patients were included, with laminectomy performed in 27 (67.5%) patients
and hemilaminectomy in 13 (32.5%) patients. Mean age was 64.2 (12.5) years, with a
significant preponderance of females (32 cases, 80.0%). Hemilaminectomy was associated
with shorter operative time (p < 0.001), faster mobilization (p < 0.001), and shorter hospital stay (<0.001). No significant statistical correlation
between tumor's volume (ccm) and operative time was found (p = 0.675; [Table 1]). At follow-up, the mean VAS score was 4.6 (1.7) among patients treated vialaminectomy
and 2.5 (1.3) among those treated viahemilaminectomy (p < 0.001). At the regression analysis, hemilaminectomy was significantly associated
with lower VAS values at follow-up (β coefficient = –2.02; 95% confidence interval
[CI]: –3.10 to –0.93, p = 0.001; adjβ = –1.54; 95% CI: –2.95 to –0.13, p = 0.033), whereas the surgical site was not related to clinical outcome at statistical
analysis (p = 0.105). Postoperative complications occurred in 1 (7.7%) and 7 (25.9%) patients
in the hemilaminectomy and laminectomy groups, respectively (p = 0.177).
Discussion
Spinal schwannomas are slow-growing tumors originating from myelinated nerve sheaths
and classified as intradural extramedullary (IDEM lesions.[1] Laminectomy extending one level above and one level below the tumor is the commonest
surgical approach,[2] granting adequate exposure, although potentially increasing the risks of postoperative
instability, especially at junctional levels.[2]
[3] This is particularly true for cervical operations, where kyphosis can cause anterior
cord compression and progressive myelopathy.[4]
[5]
Over the past 15 years, minimally invasive procedures have been gaining popularity
due reduction of the impact of the approach on spine stability, with an improvement
on postoperative pain and hospital stay.[6]
[7] Hemilaminectomy, thus, has become one of the preferred surgical approaches for either
spinal degenerative diseases or tumors.[8]
In 1991, Yasargil et al recommended the unilateral approach as the first choice of
treatment for removal of intraspinal tumors. Their recommendation was based on the
theory that unilateral hemilaminectomy exposes the ventral lateral and dorsal lateral
tumors of the spinal canal.[9]
[10]
Our surgical series of spinal schwannomas compared the unilateral hemilaminectomy
approach with conventional laminectomy and it demonstrated the safety and efficacy
of the first approach. In our study, 13 of 40 (32.5%) patients underwent tumor resection
via hemilaminectomy. Consistent with reports in other studies, we found that hemilaminectomy
was associated with faster operative time, shorter postoperative time spent in bed,
and shorter hospitalization with statistical significance.[1]
[2]
[10]
[11]
[12] Tumor volumes (ccm) were found to be unrelated to operative time at statistical
analysis (p = 0.675). Furthermore, at follow-up after 1 month, VAS score in the hemilaminectomy
group was lower than that of the laminectomy group; these data were statistically
significant. Minimal surgical trauma and preservation of vertebral column integrity
and biomechanics are factors, which might have contributed to these findings.
The rationale behind hemilaminectomy for tumor removallies on the preservation of
the contralateral hemilamina, muscles, and supraspinous/interspinous ligaments with
the integrity of the “tension band.”[9] In this and other studies, hemilaminectomy was associated with less intraoperative
blood loss, less postoperative pain, and preservation of spinal stability with more
favorable clinical outcomes.[10]
[11]
[12] In our experience, a potential disadvantage is the narrow surgical corridor left
between the spinous process and the facet joint with risks of dural and nerve root
damage or incomplete tumor removal. However, undercutting of the spinous process base,
partial facetectomy, and oblique tilting of the operating table allow a safe dissection
of the tumor. Yeo et al described another way to get more surgical space by ipsilateral
dural tacking and suture with the base of the muscle or fascia near the facet joint.[13]
This study has some limitations, such as the small number of patients, short follow-up,
and the retrospective nature. More studies are needed to confirm the findings of this
study. However, the minimally invasive approach is relatively simple and straightforward,
and provides good results in terms of total resection and postoperative quality of
life. Compared with the group treated with laminectomy, patients who underwent hemilaminectomy
experienced a shorter hospital stay, less complications, improved wound healing, faster
recovery, and less disabling cervical and/or dorsal, lumbar pain. All these benefits
allow for earlier mobilization, which is the major target for good postoperative quality
of life in patients, particularly elderly patients.
Conclusion
Unilateral hemilaminectomy has significant advantages in the removal of spinal schwannoma.
This approach allows safe and complete resection of schwannomas with good clinical
and radiologic results. Hemilaminectomy for intradural tumors offers many benefits
such as faster operative time, shorter postoperative time spent in bed, shorter hospitalization,
and less postoperative pain.
