Do Tumour Size, Type and Localisation Affect Resection Rate in Patients with Spinal Schwannoma?

Abstract

Background and Objectives: Spinal schwannomas are benign tumours that can present with various symptoms such as pain, radiculopathy and neurological deficit. Gross total resection (GTR) is of key importance for local recurrence. The aim of this study is to describe the clinical characteristics, resection rate, clinical outcome, as well as tumour recurrence, in patients with non-syndromic spinal schwannomas and to clarify which factors affect the resection rate. Materials and Methods: Patients with non-syndromic spinal schwannomas that underwent surgical resection between January 2009 and December 2018 at a single institution were included. Demographic parameters, clinical symptoms, tumour localisation and size, surgical approach and complications were noted. Factors influencing the extent of resection, the surgeon’s decision regarding the approach and the occurrence of new postoperative deficits were evaluated. Results: Fifty patients (18 females) were included. The most common presenting symptom was radiculopathy (88%). The lumbar spine was the most commonly affected site (58%). Laminotomy (72%) was the preferred surgical approach overall and specifically for exclusively intraspinal schwannomas (p = 0.02). GTR was achieved in 76.0% (n = 38). In multivariate analysis, only tumour localisation within the spinal canal (p = 0.014) independently predicted GTR, whereas the type of approach (p = 0.50) and tumour volume (p = 0.072) did not. New postoperative persisting deficits could not be predicted by any factor, including the use and alteration of intraoperative neuromonitoring. Recurrence was observed in four cases (8%) and was significantly higher in cases with STR (p = 0.04). Conclusions: In this retrospective study, GTR was solely predicted by tumour localisation within the spinal canal. The decision regarding the utilisation of different surgical approaches was solely influenced by the same factor. No factor could predict new persisting deficits. Tumour recurrence was higher in STR.

Full text


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Citation: Parlak, A.; Oppong, M.D.;
Jabbarli, R.; Gembruch, O.;
Dammann, P.; Wrede, K.;
Rauschenbach, L.; Sure, U.; Özkan, N.
Do Tumour Size, Type and Localisation
Affect Resection Rate in Patients with
Spinal Schwannoma? Medicina 2022,
58, 357. https://doi.org/10.3390/
medicina58030357
Academic Editor: Wutian Wu
Received: 7 January 2022
Accepted: 22 February 2022
Published: 1 March 2022
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medicina
Article
Do Tumour Size, Type and Localisation Affect Resection Rate in
Patients with Spinal Schwannoma?
Ahmet Parlak *, Marvin Darkwah Oppong, Ramazan Jabbarli , Oliver Gembruch , Philipp Dammann,
Karsten Wrede, Laurèl Rauschenbach, Ulrich Sure and Neriman Özkan
Department of Neurosurgery and Spine Surgery, University Hospital Essen, 45122 Essen, Germany;
marvin.darkwahoppong@uk-essen.de (M.D.O.); ramazan.jabbarli@uk-essen.de (R.J.);
oliver.gembruch@uk-essen.de (O.G.); philipp.dammann@uk-essen.de (P.D.); karsten.wrede@uk-essen.de (K.W.);
laurel.rauschenbach@uk-essen.de (L.R.); ulrich.sure@uk-essen.de (U.S.); neriman.oezkan@uk-essen.de (N.Ö.)
*Correspondence: parlakahmet@gmail.com; Tel.: +49-201-723-1201; Fax: +49-201-723-5909
Abstract:
Background and Objectives: Spinal schwannomas are benign tumours that can present with
various symptoms such as pain, radiculopathy and neurological deficit. Gross total resection (GTR) is
of key importance for local recurrence. The aim of this study is to describe the clinical characteristics,
resection rate, clinical outcome, as well as tumour recurrence, in patients with non-syndromic
spinal schwannomas and to clarify which factors affect the resection rate. Materials and Methods:
Patients with non-syndromic spinal schwannomas that underwent surgical resection between January
2009 and December 2018 at a single institution were included. Demographic parameters, clinical
symptoms, tumour localisation and size, surgical approach and complications were noted. Factors
influencing the extent of resection, the surgeon’s decision regarding the approach and the occurrence
of new postoperative deficits were evaluated. Results: Fifty patients (18 females) were included.
The most common presenting symptom was radiculopathy (88%). The lumbar spine was the most
commonly affected site (58%). Laminotomy (72%) was the preferred surgical approach overall and
specifically for exclusively intraspinal schwannomas (p= 0.02). GTR was achieved in 76.0% (n= 38).
In multivariate analysis, only tumour localisation within the spinal canal (p= 0.014) independently
predicted GTR, whereas the type of approach (p= 0.50) and tumour volume (p= 0.072) did not. New
postoperative persisting deficits could not be predicted by any factor, including the use and alteration
of intraoperative neuromonitoring. Recurrence was observed in four cases (8%) and was significantly
higher in cases with STR (p= 0.04). Conclusions: In this retrospective study, GTR was solely predicted
by tumour localisation within the spinal canal. The decision regarding the utilisation of different
surgical approaches was solely influenced by the same factor. No factor could predict new persisting
deficits. Tumour recurrence was higher in STR.
Keywords:
spinal schwannoma; peripheral nerve sheath tumours; gross total resection; recurrence
rate; subtotal resection
1. Introduction
Primary intraspinal tumours are a rare entity with an annual incidence of 1.5 per
100,000 persons. Of these, schwannomas are among the most common with an annual
incidence of 0.3–0.4 per 100,000 habitants [
1
]. Spinal schwannomas are benign, slow-
growing and encapsulated tumours that arise from Schwann cells [
2
,
3
]. The vast majority
of spinal schwannomas are sporadic and solitary lesions; only 1% of schwannomas are
related to neurofibromatosis type II (NF2), an autosomal dominant disorder characterised
by the growth of benign tumours in the nervous system [4].
Spinal schwannomas are generally intra- or extradurally located and can present with
various symptoms such as pain, radiculopathy and neurological deficit [
5
]. Schwannomas
tend to arise from the sensory nerve roots and show a much rarer involvement of motor
Medicina 2022,58, 357. https://doi.org/10.3390/medicina58030357 https://www.mdpi.com/journal/medicina

Medicina 2022,58, 357 2 of 11
nerves, which could explain radiculopathy as a common presenting symptom [
6
]. The
treatment of spinal schwannomas aims for complete resection with the preservation of
neurovascular structures [
5
]. Complete resection may depend on various factors such as
size, localisation and surgical accessibility.
Few studies have examined the factors that facilitate gross total resection (GTR) and
to what extent subtotal resection (STR) leads to tumour recurrence in patients with non-
syndromic spinal schwannomas [
7
]. In this context, the influence of the surgical approach
has also been discussed [
8
]. Recent studies have evaluated the impact of the utilisation of
intraoperative neuromonitoring (IONM) on the occurrence of new postoperative deficits,
however, with contradictory results [
9
,
10
]. The aim of this single centre study was to
identify factors affecting the resection rate of non-syndromic spinal schwannomas, as well
as predictors of postoperative new deficits and factors affecting the surgeon’s decision
regarding the surgical approach.
2. Materials and Methods
2.1. Study Population
A retrospective analysis of our dataset “Spinal neoplasms” was performed between
January 2009 and December 2018. All the patients treated at our Neurosurgical Department
due to a spinal schwannoma were included. Paediatric cases as well as patients with NF2
or schwannomatosis were excluded. The study has been carried out in accordance with
The Code of Ethics of the World Medical Association (The Declaration of Helsinki) and was
approved by the Institutional Review Board (Medical Faculty, University of Duisburg-Essen,
Registration number: 20-9650-BO).
2.2. Data Management
Digital patients’ records were reviewed and the demographic parameters, presenting
symptoms, surgical approach, necessity of instrumented stabilisation, neurological outcome
and complications were noted for each case. In cases where intraoperative monitoring
(IONM) was used, any decline of motor evoked potentials (MEP) and somatosensory
evoked potentials (SSEP) was noted by neuromonitoring technicians. Postoperative new
neurological deficits were defined as the occurrence of new neurological symptoms that
were not present at preoperative examination and persisted at first follow-up.
Pre- and postsurgical magnetic resonance (MR) imaging was examined, and tumour
localisation, size and tumour volume were calculated using Gadolinium-enhanced T1-
weighted images. For patients with clinical myelopathy, a concurrent spinal cord hyperin-
tensity on T2-weighted MR images was determined.
Multiple classifications for spinal schwannomas exist in the literature, each aiming to
provide a certain surgical guidance based upon their categorisation [
11
–
13
]. Of these, Sun
et al. have attempted to categorise spinal schwannomas according to their localisation as well
as their size, and compared the surgical outcome for each category [
14
]. The authors provide a
simple formula to estimate the size of schwannomas by considering them as ellipsoid bodies:
tumour volume = 4/3π×(craniocaudal length/2) ×transverse diameter/2)2.
As this classification categorises schwannomas according to their localisation and size,
we chose to apply it for our study. Spinal schwannomas were categorised accordingly
into four distinct localisations (I, II, III and IV) and three sizes (A, B and C). Localisation I
tumours were localised exclusively intradurally; Localisation II tumours had an intradural
localisation with an extradural extension to the nerve root foramina but were restricted to
the spinal canal; Localisation III tumours had an intradural dumbbell-shape in the spinal
canal, extending to the extraforaminal region; and Localisation IV tumours were localised
completely outside of the root foramina (Figure 1).
The patients were routinely followed-up every 6 months for 2 years after surgery. The
follow-up included neurosurgical examination and spinal MR imaging with and without
contrast agent. Tumour recurrence was defined as a new contrast-enhancing lesion at the
site of the previous excision, identified on postoperative T1-weighted MR images.

Medicina 2022,58, 357 3 of 11
Medicina 2022, 58, x FOR PEER REVIEW 3 of 11
Figure 1. The four schwannoma localisations as described by Sun et al.: (a): exclusively intradural
localisation (I), (b): intradural localisation with extradural extension to the nerve root foramina, but
restricted to the spinal canal (II), (c): intradural tumour extending to the extraforaminal region (III),
(d): localisation completely outside of the foramina (IV).
The patients were routinely followed-up every 6 months for 2 years after surgery.
The follow-up included neurosurgical examination and spinal MR imaging with and
without contrast agent. Tumour recurrence was defined as a new contrast-enhancing
lesion at the site of the previous excision, identified on postoperative T1-weighted MR
images.
2.3. Surgery
All the surgeries were performed with the use of a high-power magnification surgical
microscope in the microsurgical fashion. The approach was chosen by the surgeon based
on the localisation, size and type of the tumour. In cases where an en bloc laminoplasty
was performed, the laminae were fixed in place using osteosynthesis material with mini
fragment plates and screws (Promedics GmbH, Düsseldorf, Germany). Total resection of
the schwannoma with the preservation of the nerve root and the surrounding tissues was
attempted in all cases. En bloc resection was defined as isolating the tumour without
violating its capsule, whereas intralesional resection implicated the violation of the tumor
capsule, i.e., piecemeal resection.7 The extent of the surgery was defined according to the
surgeon’s assessment: GTR was defined as complete resection of the tumour from its
attached nerve. Watertight dural closure was pursued in intradural tumours.
Intraoperative neurophysiological monitoring (IONM) using MEP and SSEP was used in
selected cases upon the individual surgeons’ decisions. The latency and amplitude of both
median and tibial nerves were measured, and the surgeon was notified of any changes.
Figure 1.
The four schwannoma localisations as described by Sun et al.: (
a
): exclusively intradural
localisation (I), (
b
): intradural localisation with extradural extension to the nerve root foramina, but
restricted to the spinal canal (II), (
c
): intradural tumour extending to the extraforaminal region (III),
(d): localisation completely outside of the foramina (IV).
2.3. Surgery
All the surgeries were performed with the use of a high-power magnification surgical
microscope in the microsurgical fashion. The approach was chosen by the surgeon based
on the localisation, size and type of the tumour. In cases where an en bloc laminoplasty
was performed, the laminae were fixed in place using osteosynthesis material with mini
fragment plates and screws (Promedics GmbH, Düsseldorf, Germany). Total resection
of the schwannoma with the preservation of the nerve root and the surrounding tissues
was attempted in all cases. En bloc resection was defined as isolating the tumour without
violating its capsule, whereas intralesional resection implicated the violation of the tumor
capsule, i.e., piecemeal resection [
7
]. The extent of the surgery was defined according to
the surgeon’s assessment: GTR was defined as complete resection of the tumour from its
attached nerve. Watertight dural closure was pursued in intradural tumours. Intraoperative
neurophysiological monitoring (IONM) using MEP and SSEP was used in selected cases
upon the individual surgeons’ decisions. The latency and amplitude of both median and
tibial nerves were measured, and the surgeon was notified of any changes.
2.4. Endpoints
The primary endpoint was defined as GTR, whereas the secondary endpoints were
defined as the surgical approach, new neurological deficit and tumour recurrence. Peri-
procedural and mid-term complications were reported.

Medicina 2022,58, 357 4 of 11
2.5. Statistics
Statistical analysis was performed with SPSS statistical software, version 23.0 (SPSS,
Chicago, IL, USA). Factors influencing the primary and secondary endpoints of this study
were first tested in univariate analysis. Continuous variables were tested with the Student’s
t-test for normally distributed data and with the Mann–Whitney U test for non-normally
distributed data. A chi-square test was used for dichotomised variables, and for samples
with a size smaller than 5, Fisher’s exact test was used. Finally, a multivariate logistic
regression analysis was performed for the primary endpoint to identify independent
predictors upon identification in the univariate analysis and was corrected for the surgical
approach. A p-value of <0.05 was considered statistically significant.
3. Results
3.1. Cohort Characteristics
Fifty patients met the inclusion criteria. The majority of the patients were males (64%),
and the average age at presentation was 47 (
±
14) years. Radiculopathy was the most
common symptom (88%). The interval between the first symptoms and surgical treatment
was 16 (
±
35) months. The most common tumour localisation was lumbosacral (58%). Most
schwannomas were smaller than 2 cm
3
. Schwannomas extending to the extraforaminal
region (Localisation III schwannomas) were the most common type (36%). The average
tumour volume was 9.7 (0.10–93.50) cm
3
, with 0.85 cm
3
for Size A, 2.77 cm
3
for Size B and
24.34 cm
3
for Size C. Clinical myelopathy with concurrent spinal cord T2-hyperintensity
on MR imaging was present in six (12%) cases. IONM was used in 22 cases (44%). Gross
total resection, including en-bloc resections in 18 cases, was performed in the majority of the
patients (76%), whereas STR was achieved in 12 cases (24%). Tumour recurrence occurred
in one patient with GTR (2.6%) and three patients with STR (30%) (p= 0.04). The average
follow-up was 30 (±27) months; five patients were lost to follow-up (Table 1).
Table 1. Patient and tumour characteristics.
n%
Gender Female 18 36
Age (years) a46 (±14)
Clinical presentation Symptoms related to tumor: 46 92
Radiculopathy b44 88
Spinal deficit 11 22
Unrelated symptom(s) leading
to diagnosis 4 8
Time between first symptoms
and diagnosis (months) 16 (35)
Tumour characteristics
(MR imaging)
Tumour localisation Cervical 15 30
Thoracal 6 12
Lumbosacral 29 58
Central 9 18
Lateral: 41 82
Right 21 42
Left 20 40
Volume of tumour (cm3)Mean volume a9.7 (18.8)
Size A (0–2) 22 44
Size B (2–6) 12 24
Size C (>6) 16 32
Localisation type I 17 34
II 11 22
III 18 36
IV 4 8
Presence of myelopathy yes 6 12
aMean (SD); bRadiculopathy was defined as paresis, hypaesthesia, paraesthesia as well as dysaesthesia.

Medicina 2022,58, 357 5 of 11
3.2. Surgical Approach and Complications
The most common surgical approach was laminotomy (72%) including laminoplasty
(54%) and laminectomy (18%). This technique provides a wide view on the posterior aspect
of the spinal canal. A hemilaminectomy as a unilateral approach sufficed in 12 cases (24%).
Instrumented stabilisation was performed in one case with a large C3 schwannoma, which
was accessed via laminectomy of C3 and C4 and right-sided facetectomy. One case of a
type IV mainly extraforaminal schwannoma at Th1 was operated via an extraforaminal
approach. Surgical related complications occurred in five cases. Cerebrospinal fluid leakage
was observed in four patients and required surgery in three cases. An epidural abscess
occurred in one patient requiring the removal of the laminoplasty block.
3.3. Predictors of GTR
No significant differences were found in tumour localisation and resection rate. Uni-
variate analysis showed that GTR was more common in Size A tumours (p= 0.004, odds
ratio (OR) = 13.59, 95% confidence interval (95% CI) 1.59–116.3) and in Localisation I
(
p= 0.004
, OR = 1.81, 95% CI 1.36–2.41), as well as in Localisation II (p= 0.05, OR = 1.41,
CI 1.15–1.72) tumours. Respectively, STR was more common in Size C tumours (p< 0.001,
OR = 0.04, CI 0.01–0.22) and Localisation III tumours (p< 0.001, OR 0.21, CI 0.02–0.19).
Multivariate analysis identified Localisation III tumours (p= 0.014, adjusted (a) OR = 0.41,
95% CI 0.01–0.052) as an independent predictor for the extent of resection, but not the type
of approach (p=0.50, aOR = 0.49, 95% CI 0.06–3.83) or Size C tumours (p= 0.072,
aOR = 0.15
,
95% CI 0.02–1.18).
3.4. Factors Influencing the Surgical Approach
In univariate analysis, the only factor impacting the chosen approach was for Localisation I
tumours (72% laminotomy vs. 24% hemilaminectomy; p= 0.018, OR = 10.40, 95% CI 1.23–88.18).
All other factors including tumour volume, location and myelopathy did not significantly affect
the surgeon’s decision on the way of accessing the tumour (Table 2).
Table 2. Univariate analysis.
Primary Endpoints
GTR STR p-
Value OR 95% CI
Tumour size
A 21 1 0.004 13.59 1.59–116.03
B 11 1 0.248 4.48 0.52–39.01
C 6 10 <0.001 0.04 0.01–0.22
Localisation type
I 17 0 0.004 1.81 1.36–2.41
II 11 0 0.046 1.41 1.15–1.72
III 7 11 >0.001 0.21 0.02–0.19
IV 3 1 >0.99 0.94 0.09–10.01
Secondary endpoints
Laminotomy Hemilaminectomy
Tumour size
A 16 6 0.919 1.07 0.31—-3.71
B 9 3 >0.99 1.22 0.28–5.38
C 11 5 0.746 0.79 0.22–2.92
Localisation type
I 16 1 0.018 10.40 1.23–88.18
II 9 2 0.705 2.00 0.37–10.69
III 10 8 0.052 0.29 0.08–1.04
IV 1 3 0.061 0.11 0.01–1.11
Myelopathy 5 1 0.663 2.01 0.22–19.75

Medicina 2022,58, 357 6 of 11
Table 2. Cont.
Primary Endpoints
GTR STR p-
Value OR 95% CI
Persisting deficits
(n = 6)
No new deficits
(n = 44)
IONM 2 20 0.683 0.60 0.10–3.62
IONM alteration 0 3 >0.99 1.00 0.04–25.69
Resection intralesional 4 29 >0.99 1.03 0.17–6.31
Myelopathy 0 6 >0.99 0.52 0.02–9.10
GTR 4 34 0.621 0.588 0.09–3.67
Tumour size
A 2 20 0.683 0.60 0.10–3.62
B 2 10 0.621 1.70 0.27–10.68
C 2 14 >0.99 1.07 0.18–6.56
Tumour localisation
I 2 9 0.601 1.94 0.31–12.35
II 3 15 0.654 1.93 0.35–10.77
III 0 4 >0.99 0.69 0.03–14.43
IV 2 9 0.601 1.94 0.31–12.35
3.5. Predictors of New Postoperative Deficits
New persisting neurological deficits were noted in six cases: hypaesthesia in four
cases, low grade paresis (Medical Research Council Scale 4) in two cases and neurological
bladder, bowel and sexual dysfunction in one case with a giant lumbosacral schwannoma,
complicated with postoperative cerebrospinal fluid leakage. Alterations during IONM
occurred in three patients (MEP decline of the left tibial nerve in two patients and SSEP
decline of the right median nerve in one patient) of which only one patient had a persisting
new weakness in dorsiflexion as well as plantarflexion MRC 4. No alterations in MEP as
well as SSEP were recorded in three patients that had a new persisting sensory deficit.
In univariate analysis, we were not able to identify any predictors of new persisting
deficits among tumour location, size and type (Table 1). Furthermore, the approach as well
as the use and alteration of IONM (p= 0.718, OR = 1.13, 95% CI 0.31–4.22 and p> 0.99,
OR = 0.53, 95% CI 0.04–7.49, respectively) did not predict new persisting deficits.
4. Illustrative Case
A 24 year old female patient presented in our clinic complaining of neck pain and
involuntary movements of both arms. No focal deficits were observed in the neurolog-
ical examination. MR imaging showed a large intradural contrast-enhancing tumour,
expanding from 5th cervical vertebra to the 1st thoracic vertebra, with intramedullary cord
hyperintensity at T2-weighted MR imaging. The patient was positioned in a prone position
and the head was fixed with the use of a Mayfield clamp. A laminotomy from the 4th
cervical vertebra up to the 1st thoracic vertebra was performed. Midline durotomy was
performed and the tumour was removed in toto with the help of an ultrasonic aspirator. A
temporary decrease in SEP signals on both sides of up to 50% was noticed, whereas MEP
signals remained constant during the whole procedure. After watertight dura closure, the
laminotomy block was put into place and fixed with mini plates and screws. Postoper-
atively, the patient had no new focal neurological deficits. Eleven months of follow-up
showed no tumour recurrence. Figures 2and 3.

Medicina 2022,58, 357 7 of 11
Medicina 2022, 58, x FOR PEER REVIEW 7 of 11
position and the head was fixed with the use of a Mayfield clamp. A laminotomy from the
4th cervical vertebra up to the 1st thoracic vertebra was performed. Midline durotomy
was performed and the tumour was removed in toto with the help of an ultrasonic
aspirator. A temporary decrease in SEP signals on both sides of up to 50% was noticed,
whereas MEP signals remained constant during the whole procedure. After watertight
dura closure, the laminotomy block was put into place and fixed with mini plates and
screws. Postoperatively, the patient had no new focal neurological deficits. Eleven months
of follow-up showed no tumour recurrence. Figures 2 and 3.
Figure 2. MR Imaging (T2-weighted on the left, T1 with gadolinium on the right) showing a large
intradural, contrast-enhancing lesion (marked with asterisk) compressing the cervical spinal cord
(a,b). Postoperative MR Imaging showing no signs of tumour recurrence (c,d).
Figure 2.
MR Imaging (T2-weighted on the left, T1 with gadolinium on the right) showing a large
intradural, contrast-enhancing lesion (marked with asterisk) compressing the cervical spinal cord (
a
,
b
).
Postoperative MR Imaging showing no signs of tumour recurrence (c,d).

Medicina 2022,58, 357 8 of 11
Medicina 2022, 58, x FOR PEER REVIEW 8 of 11
Figure 3. Intraoperative view after showing a large intradural schwannoma (marked with asterisk).
The schwannoma is mobilised cranially, the compressed spinal cord is visible caudally.
5. Discussion
The aim of this study was to clarify which factors affect the resection rate of non-
syndromic spinal schwannomas. We additionally sought to identify predictors for
postoperative new deficits as well as factors affecting the surgeon’s decision regarding the
surgical approach.
In this single centre retrospective cohort study of 50 patients, we identified that GTR
was more likely in solely intraspinal located schwannomas and schwannomas smaller
than 2 cm3. Consequently, STR was more common in schwannomas larger than >6 cm3
and in intraspinal schwannomas extending into the extraforaminal region. The same
finding was observed in a large multicentre database, showing that tumour recurrence is
higher in large sized tumours, with the extent in the cranial–caudal direction posing the
greatest hazard.7 However, it should be noted that GTR in larger tumours and tumours
extending into the extraforaminal region may be possible with a more extensive surgery,
requiring a second surgery and stabilisation.
Tumour localisation within the different spinal sections was not found to affect the
resection rate. In our cohort, GTR was achieved in 76% of the cases, which included 18
cases with en-bloc resection of the tumour. This is within the range of previous reports
[5,15–17]. In a previous study, en-bloc resection of spinal schwannomas in 34 patients
resulted in new postoperative sensory deficits in 16 patients [5]. We observed no new
deficits following en-bloc resection in our cohort study.
Tumour recurrence occurred in one patient in which GTR was performed, whereas
three of the twelve patients that received a subtotal resection had tumour recurrence.
Previous studies report a recurrence rate between 4% and 9% despite GTR [5,15,16,18]. No
significant difference was found between en-bloc and intralesional resection in our study.
In contrast, Fehlings et al. demonstrated a four-fold risk increase in tumour recurrence in
patients who underwent intralesional resection [7]. It is noteworthy that GTR was
according to the surgeon’s assessment which may yield a bias to the resection rate.
Assessing the resection rate of benign spinal tumours via, e.g., early postoperative MR
imaging has not been well described in the literature. Our study was performed in line
with previous studies by assessing the resection rate via MR imaging after 3 months [7,16].
Figure 3.
Intraoperative view after showing a large intradural schwannoma (marked with asterisk).
The schwannoma is mobilised cranially, the compressed spinal cord is visible caudally.
5. Discussion
The aim of this study was to clarify which factors affect the resection rate of non-
syndromic spinal schwannomas. We additionally sought to identify predictors for post-
operative new deficits as well as factors affecting the surgeon’s decision regarding the
surgical approach.
In this single centre retrospective cohort study of 50 patients, we identified that GTR
was more likely in solely intraspinal located schwannomas and schwannomas smaller than
2 cm
3
. Consequently, STR was more common in schwannomas larger than >6 cm
3
and
in intraspinal schwannomas extending into the extraforaminal region. The same finding
was observed in a large multicentre database, showing that tumour recurrence is higher
in large sized tumours, with the extent in the cranial–caudal direction posing the greatest
hazard [
7
]. However, it should be noted that GTR in larger tumours and tumours extending
into the extraforaminal region may be possible with a more extensive surgery, requiring a
second surgery and stabilisation.
Tumour localisation within the different spinal sections was not found to affect the
resection rate. In our cohort, GTR was achieved in 76% of the cases, which included 18 cases
with en-bloc resection of the tumour. This is within the range of previous reports [
5
,
15
–
17
].
In a previous study, en-bloc resection of spinal schwannomas in 34 patients resulted in new
postoperative sensory deficits in 16 patients [
5
]. We observed no new deficits following
en-bloc resection in our cohort study.
Tumour recurrence occurred in one patient in which GTR was performed, whereas
three of the twelve patients that received a subtotal resection had tumour recurrence.
Previous studies report a recurrence rate between 4% and 9% despite GTR [
5
,
15
,
16
,
18
]. No
significant difference was found between en-bloc and intralesional resection in our study.
In contrast, Fehlings et al. demonstrated a four-fold risk increase in tumour recurrence in
patients who underwent intralesional resection [
7
]. It is noteworthy that GTR was according
to the surgeon’s assessment which may yield a bias to the resection rate. Assessing the
resection rate of benign spinal tumours via, e.g., early postoperative MR imaging has not
been well described in the literature. Our study was performed in line with previous
studies by assessing the resection rate via MR imaging after 3 months [7,16].

Medicina 2022,58, 357 9 of 11
Laminotomy was identified as the preferred surgical approach in exclusively intradu-
ral schwannomas. This approach provides a broad view of the dorsal spinal cord and can
be useful in the resection of tumours extending beyond the spinal canal. Hemilaminectomy,
a technique reported as a safe and effective approach in spinal tumour resection, sufficed
in 24% (12 cases) [
19
]. None of the other factors such as tumour volume, location and
myelopathy significantly affect the surgeon’s decision on the way of accessing the tumour.
It should be emphasised that surgical approach can be institution- and surgeon-dependent.
The use of minimally invasive techniques and endoscopic approaches may be useful in
selected cases [20,21].
New persisting neurological deficits were noted in six cases. Tumour location, size
and type were not a predictor for persisting new deficits. Furthermore, the approach as
well as the use and alteration of IONM did not predict new persisting deficits. IONM is
recommended for resections of intra- and extramedullary tumours, however, the added
value during excision of schwannomas has been debated [
10
,
22
,
23
]. Although some au-
thors report an increase in safety during spinal schwannoma surgery, some authors state
that intraoperative monitoring is not able to detect roots vulnerable to injury [
9
]. We
observed the same finding, as none of the patients with intraoperative signal decline had
permanent neurological deficits and as one patient without any signal decline had a new
persisting sensory deficit. The added value of IONM in schwannoma surgery requires
further research.
This cohort study has several limitations. First, the retrospective art of the study may
have resulted in selection and information bias. Second, the method used for tumour
size calculation assumes that all spinal schwannomas are ellipsoid-shaped. Third, the
recurrence rate may also depend on proliferation indices such as Ki-67, which was not
investigated in our study as this factor was not determined for each case [
15
]. Fourth, the
average follow-up was 30 months and five patients were lost to follow-up. Because of the
slow-growing attribute of spinal schwannomas, more extensive follow-up is advisable.
6. Conclusions
Our findings suggest that GTR is more likely to be achieved in smaller schwannomas
independent of localisation. The surgical approach did not affect the resection rate. STR
is observed in tumours extending into the neuroforamen and is associated with a higher
tumour recurrence rate. New postoperative persisting deficits could not be predicted by
any factor, including the use and alteration of IONM. Future prospective clinical studies
are required for a more accurate understanding of the factors contributing to GTR in spinal
schwannomas as well as recurrence rates in STR. Finally, IONM was not used in each
individual case.
Author Contributions:
Conceptualisation, analysis, writing, A.P.; conceptualisation, data collection,
analysis, interpretation, revision, M.D.O.; revising, R.J.; revising, drafting, O.G.; revising, P.D.;
revising, K.W.; revising, methodology, L.R.; revising, approval, U.S.; conceptualisation, analysis,
drafting, revision and approval, N.Ö. All authors have read and agreed to the published version of
the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement:
This study has been carried out in accordance with The
Code of Ethics of the World Medical Association (The Declaration of Helsinki) and was approved by
the Institutional Review Board (Medical Faculty, University of Duisburg-Essen, Registration number:
20-9650-BO).
Informed Consent Statement:
Informed consent was obtained from all subjects involved in the study.
Data Availability Statement:
The authors confirm that the raw data that support the findings of this
study are available from the corresponding author upon request.
Acknowledgments:
We acknowledge support by the Open Access Publication Fund of the University
of Duisburg-Essen.

Medicina 2022,58, 357 10 of 11
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
Gross total resection GTR
Magnetic resonance imaging MRI
Neurofibromatosis type II NF2
Subtotal resection STR
Intraoperative neuromonitoring IONM
MEP motor evoked potentials
SSEP somatosensory evoked potentials
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