Keywords
antibiotic prophylaxis - extent of resection - intraoperative MRI - surgical site
infections - glioblastoma - histopathology
Introduction
Reducing tumor volumes as much as possible and enabling good neurologic outcomes comprise
a major task in neurosurgery. An extent of resection (EOR) > 98% is accepted as a
positive prognostic factor for survival of glioblastoma (GBM) patients.[1]
[2] Reduction of tumor volumes as much as possible is also recommended for low-grade
gliomas.[3] Moreover, it is also important in the surgical treatment of pituitary adenomas to
achieve a gross total resection (GTR) because it is known to decrease the rate of
recurrence.[4] Intraoperative imaging such as fluorescence, ultrasound, or intraoperative MRI (iMRI)
are powerful tools to determine the EOR of those diseases.
The second task that must be considered in the surgical treatment of intracranial
lesions is compensating for brain shift that depends on tumor size, localization of
tumor, surrounding brain edema, positioning of the patient, type of neurosurgical
approach, administration of osmotic diuretics, and the opening of the ventricular
system.[5] Mean brain shift of tumor margins, sulci, third ventricle, and lateral ventricles
has been observed from 6 to 9 mm.[6] Using iMRI in combination with neuromonitoring and mapping represents an excellent
tool to achieve maximal surgical results and ensure a good postoperative neurologic
outcome. Furthermore, with iMRI, neuronavigation can be updated to compensate for
brain shift. Despite the advantages of iMRI, it is not yet universally established
because of high purchase price and operating costs. Furthermore, it is suggested that
an iMRI in dual use causes a higher infection rate, and recent data estimated the
cost for surgical site infection (SSI) after craniotomy to be £9,283.[7]
To perform neurosurgical procedures in an iMRI suite, excellent hygiene must be maintained
to ensure low rates of SSI. Generally, 5% is the accepted threshold for SSI in neurosurgery.[8] A 2017 study including 132,063 patients showed that the postoperative infection
rate in neurosurgical procedures is 5.3%.[9] Because of highly varying surgical conditions, there are also reports of SSI rates
ranging between 1% and 11%.[7]
[10]
[11]
[12]
[13]
[14]
Due to increasing rates of SSI caused by multiresistant bacteria, use of perioperative
antibiotic prophylaxis is highly debated. Recent data showed that lincosamides, glycopeptides,
third-generation cephalosporins, other combinations of prophylactic antibiotics, or
antibiotics in the penicillin family alone are better prophylaxis against SSI than
first-generation cephalosporins among neurosurgical patients,[15] indicating a need to cover multiresistant and gram-negative bacteria. The use of
vancomycin is still controversial because of its adverse effects and increasing rates
of vancomycin-resistant enterococci.[16] Other studies of shunt surgery and studies in which vancomycin was administered
in the subgaleal space reported a beneficial outcome.[17]
[18] We assessed the clinical routine in our iMRI suite that is in dual use for both
diagnostic and intraoperative neurosurgical imaging. We focused on analyzing the success
of surgery, evaluating the resection rates, histopathologic accuracy of iMRI-guided
resections, safety of the iMRI suite concerning SSI, and cefazolin only versus additional
intrathecal administration of vancomycin and gentamicin antibiotic prophylaxis in
all GBM procedures performed in the dual-use iMRI suite.
Methods
Study Design
All data were analyzed retrospectively. Surgeries were performed between July 1, 2011,
and June 31, 2015. Primary, secondary, recurrent, and irradiated GBMs were included
in the group of 79 GBM patients. Ethical approval was received by a university committee.
Specific consent of the patients to take part in this retrospective study was not
necessary. All personal data of patients were anonymized.
Intraoperative Imaging Techniques
5-Aminolevulinic Acid
5-Aminolevulinic (5-ALA) was administered orally as a single dose (20 mg/kg body weight)
an average of 3 hours (range: 2–5 hours) preoperatively in 68 GBM patients. For visualization
of the fluorescence, we used the PENTERO 600 microscope (Zeiss, Oberkochen, Germany)
with an integrated head-up display to visualize the neuronavigation and a filter to
visualize 405 nm fluorescence.
Intraoperative MRI and Corresponding Equipment
All examinations were performed in a 1.5-T iMRI (Philips Diamond Select Achieva 1.5
T; Philips, Amsterdam, Netherlands) with the administration of 0.1 mmol GD-DTPA/kg
body weight when enhancing tumor tissue was seen in the preoperative MR images. The
iMRI suite ([Fig. 1]) allows a dual use of the MR system.
Fig. 1 Drawing of the layout of the intraoperative magnetic resonance imaging suite.
The system can be shared for daily diagnostic use for inpatients and outpatients,
and for intraoperative imaging because of the separate entrance through double doors
from the operating room. On the day of surgery the iMRI suite is reserved for 3 hours
for the intraoperative imaging procedure. The iMRI suite gets cleaned like a regular
surgical suite the evening before and also 1 hour before iMRI scanning. The MR suite
is equipped with operative air conditioning that has to be started 30 minutes before
intraoperative scanning begins. A sterile cover of the patient is essential for the
whole procedure to maintain hygienic conditions. Consequently, before skin incision
one sterile cover has to be applied above the head. After the conventional resection
with neuronavigation and 5-ALA, a second sterile cover is placed on the patient before
the upper head coil of the MRI is integrated into the skull clamp. Afterward, the
whole setup is wrapped in a sterile cover reaching over the head and below the shoulders
([Fig. 2]). For the sterile cover, positioning and transport in and out of the iMRI one hour
is calculated. After the whole procedure is finished, the iMRI suite gets cleaned
again before diagnostic imaging is continued.
Fig. 2 Sterile cover of a patient transported into the intraoperative magnetic resonance
imaging suite.
All patients were registered on the neuronavigation system (Brainlab Curve, Brainlab,
Feldkirchen, Germany) using preoperative T1 magnetization-prepared rapid acquisition
with gradient echo (MPRAGE) scans and a Softouch registration pointer (Brainlab, Feldkirchen,
Germany). Patients' heads were fixed in position with the Noras Head Holder-kit Heidberg
(Noras, Würzburg, Germany). The Alpha Maquet Plus (MR-compatible table) (Maquet, Rastatt,
Germany) was used during surgery and for transporting the patient into the MR suite.
Surgical Procedure
[Fig. 3] shows our surgical workflow for GBM surgery. Initially, a white-light resection
under neuronavigation guidance was performed. When the surgeon assumed that GTR of
the tumor was achieved, hemostasis followed. Afterward the resection cavity was examined
using 5-ALA, and areas suspicious for remaining tumor tissue were resected. Then the
patient was transported into the iMRI according to a specific protocol and controlled
by a physician using a checklist. After completing the iMRI scan, images were evaluated
by the neuroradiologist and neurosurgeon concerning residual contrast enhancement.
If no residual enhancement was visible, surgery was finished. In all remaining cases
with residual enhancement, the resection cavity was reexamined by re-referencing the
neuronavigation using the intraoperative MR images. If suspicious tumor was in a noneloquent
area, iMRI-guided resection was performed.
Fig. 3 Surgical workflow. 5-ALA, 5-aminolevulinic acid; iMRI, intraoperative magnetic resonance
imaging.
Volumetric Segmentation and Definition of GTR and EOR
Volumetric segmentation of GBMs was performed using Aquarius intuition software (Terarecon,
Houston, Texas, United States). We analyzed contrast-enhanced T1-weighted 1.5-T MRI
scans with a semiautomatic volumetric tumor segmentation algorithm ([Fig. 4]). Pre-, intra-, and postoperative (obtained within 72 hours after surgery) MRI scans
were examined.
Fig. 4 Volumetric segmentation of preoperative and intraoperative contrast-enhanced T1-weighted
magnetic resonance imaging scans.
GTR was defined as removal of ≥ 95% of enhancing tissue and the loss of nodular enhancement,
and subtotal resection as the removal of < 95% of the enhancing tumor tissue. EOR
was determined by comparing preoperative and postoperative (obtained within 72 hours
after surgery) tumor volumes on MRI scans.
Histologic Analysis
Histologic evaluation was performed according to the World Health Organization 2007
diagnostic consensus criteria.[19] For this purpose, paraffin sections were stained with hematoxylin and eosin. Sections
were examined immunohistochemically with MIB-1 antibody, GFAP, and IDH1. MGMT status
was determined by methylation-specific polymerase chain reaction.
Antibiotic Prophylaxis
Perioperative antibiotic prophylaxis was used in 79 patients and in two different
combinations. One group of 50 patients received only cephalosporins (2 g cefazolin
or 1.5 g cefuroxime) intravenously at anesthesia introduction. Another group of 29
patients received in addition to the intravenous cephalosporin a single intrathecal
antibiotic prophylaxis composed of vancomycin (20 mg) and gentamicin (5 mg) shortly
before closing the dura mater. The intrathecal antibiotic prophylaxis was injected
into the resection cavity at the end of the operation after completion of hemostasis,
shortly before the closure of the dura.
The additional administration of vancomycin and gentamicin was part of a change of
the perioperative antibiotic prophylaxis protocol in our department after the introduction
of the MRI in 2011. Patients with risk factors associated with SSI (diabetes mellitus,
obesity, long-term corticosteroid use, recently received radiotherapy or chemotherapy)
and the absence of acknowledged contraindications for vancomycin and gentamicin were
candidates for the intrathecal antibiotic prophylaxis.
Definition of Surgical Site Infections
SSIs were identified based on postoperative clinical notes with the use of the Centers
for Disease Control and Prevention definition of infection (infection involving superficial
incisional, deep incisional, and/or organ/space SSI).[20] Definition of SSI was not limited to a period of 30 days after surgery. Infections
diagnosed at any time in the follow-up period were included. Wound dehiscences without
evidence of infection were not considered as an SSI. Superficial SSIs were defined
as infections affecting the cutis and subcutis and caused by cutaneous bacteria. Deep
SSIs included meningitis, brain abscess, subdural empyema, and cerebritis. The following
parameters were examined in patients with SSI: symptoms, risk factors for SSI, evidence
of specific bacteria from cultures, cerebrospinal fluid parameters, C-reactive protein,
and white blood cell count. To evaluate the etiology of SSIs, we analyzed preexisting
illness, age, sex, scanning time, need for additional resections, previous surgery
with craniotomy, perioperative antibiotic prophylaxis, and causative agent.
Statistical Methods
Descriptive and exploratory methods were used to analyze the data. We calculated mean
values, standard error of the mean, and performed chi-square tests. Missing data were
not included in our calculations. We calculated positive predictive value (PPV), negative
predictive value (NPV), and sensitivity and specificity of iMRI to detect tumor tissue.
Confidence intervals (CIs) were calculated to assess the necessity of additional resections
to achieve GTR. Pearson's chi-square tests (two sided) were performed to compare the
two kinds of antibiotic prophylaxis, age, sex, previous surgery with craniotomy, and
risk factors (diabetes mellitus, obesity, long-term corticosteroid use, recently received
radiotherapy or chemotherapy) concerning the incidence of SSI. Student two-sample
t tests were conducted to analyze mean values. For all statistical tests and graphics,
we used SPSS v.23 (IBM Corp., Armonk, New York, United States) and Microsoft Excel
2016 (Microsoft Corp., Redmond, Washington, United States).
Results
Characteristics of Patients with Glioblastomas
In all, 79 surgical procedures in patients with GBM were performed within the iMRI
suite. [Table 1] shows the general characteristics of the GBM patient collective. Most of the patients
had primary GBMs The rate of tumors located in eloquent areas was quite high (45.6%).
All patients showed the typical, strong, peripheral ring gadolinium (Gd) enhancement
in preoperative MRI scans. In all, 68 patients received 5-ALA before surgery, and
58 of them showed a strong intraoperative fluorescence; therefore, the correlation
between Gd enhancement on preoperative T1-weighted contrast-enhanced MRI and positive
5-ALA fluorescent reaction was 85.29%.In all cases we performed an iMRI only once.
Table 1
Patient characteristics
|
GBM patient characteristics (n = 79)
|
|
|
|
Characteristic
|
|
|
|
Male-to-female ratio
|
|
1.82:1
|
|
Mean age, y
|
|
58.6 (SD ± 12.1)
|
|
Mean MIB-I value
|
|
32.6 (SD ± 17.6)
|
|
IDH1 point mutation (%)
|
|
8 (10.8)
|
|
MGMT promoter hypermethylation (%)
|
|
20 (25.3)
|
|
Affected lobe (%)
|
Temporal
|
28 (35.4)
|
|
Frontal
|
21 (26.6)
|
|
Parietal
|
16 (20.3)
|
|
Occipital
|
6 (7.6)
|
|
Multilobular
|
8 (10.1)
|
|
Left-sided lesions (%)
|
|
37 (46.8)
|
|
Eloquent areas (%)
|
|
36 (45.6)
|
|
Mean tumor volume, cm3
|
|
29.43
|
|
No. of additional resections after iMRI (%)
|
|
55 (69.6)
|
Abbreviations: GBM, glioblastoma; IDH1, isocitrate dehydrogenase; iMRI, intraoperative
magnetic resonance imaging; MGMT, O6-methylguanin-DANN methyltransferase; MIB-I, Molecular
Immunology Borstel; SD, standard deviation.
Surgical Success with iMRI-guided Glioblastoma Resection
Extent of Resection
EOR was determined in 74 of 79 patients. Five cases were excluded due to low and/or
diffuse contrast-enhancing properties in pre- or postoperative MRI scans making reliable
segmentation of T1-weighted contrast-enhanced MR images nearly impossible, as judged
by a neuroradiologist. The mean EOR was 96.27%. [Table 2] summarizes the determined tumor volumes.
Table 2
Determined values of volumetric tumor segmentation
|
Volumetric segmentation
|
iMRI
|
|
Variables
|
|
|
Mean preoperative tumor volume, cm3
|
29.43
|
|
Range
|
1.16–121
|
|
SEM
|
25.8
|
|
Mean intraoperative tumor volume, cm3
|
5.3
|
|
Mean postoperative tumor volume, cm3
|
0.565
|
|
Range
|
0–5.97
|
|
SEM
|
1.67
|
|
Mean EOR, %
|
96.27
|
|
Range
|
16.56–100
|
|
SEM
|
11.04
|
Abbreviations: EOR, extent of resection; iMRI, intraoperative magnetic resonance imaging;
SEM, standard error of the mean.
Rate of Subtotal and Gross Total Resection Before and After Extended Resections
GTR was determined at two different time points. At the time of iMRI, GTR was found
in 28 patients (35.44%). After iMRI and additional resection, a GTR was achieved in
59 of the 79 GBM patients (74.68%; p < 0.0001). Thus, iMRI helped to achieve GTR in additional 31 patients: 52.54% of
all patients with a GTR in the postoperative MRI benefited from iMRI-guided additional
resections. [Fig. 5] shows the increase in surgical success using iMRI. The CI to achieve GTR by iMRI-guided
extended resection was also calculated (95% CI, 0.56–0.84).
Fig. 5 Rate of gross total resection: before and after interoperative magnetic resonance
imaging (MRI)–guided additional resections.
Histopathology of iMRI-guided Additional Resections
In 55 of 79 (69.6%) GBM operations, we performed additional resections because iMRI
showed residual Gd enhancement. The PPV, that the contrast enhancement in iMRI corresponds
to tumor, was 88.6%. In the specimens of 45 of 55 patients in whom iMRI-guided additional
resections were performed, tumor tissue could be confirmed. Sensitivity was 100% and
specificity was 70.6%. The NPV was 100%. [Table 3] shows the histopathologic assessment.
Table 3
Histopathologic analyses of iMRI-guided extended resections of glioblastoma
|
Histopathologic assessment, %
|
|
|
Sensitivity
|
100
|
|
Specificity
|
70.6
|
|
Positive predictive value
|
88.6
|
|
Negative predictive value
|
100
|
Abbreviation: iMRI, intraoperative magnetic resonance imaging.
Surgical Site Infections
The mean duration of the scanning time in the iMRI was 33.6 ( ± 7.17) minutes. Four
of the 79 patients (5.06%) had an SSI. There were two superficial SSIs, one subdural
empyema and one cerebritis ([Table 4]). Mean duration of the scanning time in cases with an SSI was 29 minutes and failed
to be a statistically significant variable. Overall, 28 (35.44%) of the patients had
a previous craniotomy and were treated because of recurrence. SSI was observed in
two (7.14%) of the recurrent gliomas. Two of the four patients with SSI had risk factors
such as prior radiochemotherapy and morbid obesity. In two of the four patients, we
performed an extended resection after iMRI. [Table 5] shows the cases with SSIs in detail.
Table 4
Overview of surgical site infections
|
Overall rate of SSIs
|
4 (5.06%)
|
|
Superficial SSI
|
2 (2.53%)
|
|
Subdural empyema
|
1 (1.27%)
|
|
Cerebritis
|
1 (1.27%)
|
Abbreviation: SSI, surgical site infection.
Table 5
Details of patients with surgical site infections
|
Cases with SSI
|
|
Age, y/Sex
|
Infection
|
Pathogenic bacteria
|
Antibiotic prophylaxis
|
No. of additional resections
|
Second surgery for recurrent glioma
|
Risk factors
|
Duration of iMRI scan, min
|
|
65/M
|
Sf SSI
|
Staphylococcus epidermidis
|
2 g cefazolin
|
1
|
Yes
|
Previous radiotherapy and chemotherapy
|
20
|
|
65/F
|
Sf SSI
|
Enterobacter cloacae
|
2 g cefazolin
|
0
|
No
|
–
|
33
|
|
54/M
|
Subdural empyema
|
Staphylococcus aureus
|
2 g cefazolin
|
0
|
No
|
Morbid obesity
|
30
|
|
58/M
|
Cerebritis
|
Pseudomonas aeruginosa
|
2 g cefazolin
|
1
|
Yes
|
–
|
30
|
Abbreviations: F, female; iMRI, intraoperative magnetic resonance imaging; M, male;
Sf, superficial.
The correlation between SSI and administered antibiotic prophylaxis was examined in
the 79 patients. In 50 patients who received only intravenous antibiotic prophylaxis
(cefazolin or cefuroxime), four SSIs (8%) occurred. In the second group of 29 patients
who received additional intrathecal antibiotic prophylaxis (vancomycin and gentamicin),
no SSIs were observed (p = 0.133). Age, sex, risk factors in medical history, previous surgery, preoperative
tumor volumes, duration of surgery, and need of additional resections were also analyzed
and not statistically significant concerning the rate of SSI ([Tables 6] and [7]).
Table 6
Univariate analysis of risk factors for SSI
|
Variables
|
Rates of SSI
|
Rates of SSI
|
p Value
|
|
Age, y (%)
|
> 65: 0/20 (0)
|
< 65: 4/59 (6.8)
|
0.23
|
|
Sex (%)
|
Female: 1/28 (3.6)
|
Male: 3/51 (5.9)
|
0.654
|
|
Risk factors (%)
|
Yes: 2/16 (12.5)
|
No: 2/63 (3.2)
|
0.129
|
|
Second surgery for recurrent glioma (%)
|
Yes: 2/28 (7.14)
|
No: 2/51 (3.9)
|
0.532
|
|
iMRI-guided additional resections (%)
|
Yes: 2/55 (3.6)
|
No: 2/24 (8.3)
|
0.381
|
|
Duration of surgery, h (%)
|
≥ 4 h: 2/56 (3.6)
|
≤ 4 h: 2/23 (8.7)
|
0.345
|
|
Perioperative antibiotic prophylaxis (%)
|
Parenteral plus intrathecal antibiotics: 0/29 (0)
|
Parenteral antibiotics: 4/50 (8)
|
0.133
|
Abbreviations: iMRI, intraoperative magnetic resonance imaging; SSI, surgical site
infection.
Table 7
Tumor volumes and duration of surgery as risk factors for SSI (two-sample t test)
|
Variables
|
SSI
|
No SSI
|
p Value
|
|
Preoperative tumor volume, cm3, mean value and sEM
|
26.57 ± 17.77
|
29.58 ± 27.94
|
0.79
|
|
Duration of surgery, min, mean value and SEM
|
246.25 ± 19.16
|
245.53 ± 23.07
|
0.953
|
Abbreviations: SEM, standard error of the mean; SSI, surgical site infection.
Discussion
Despite continuous improvement in neurosurgical techniques, GBM still represents a
fatal diagnosis. Complete tumor resection (EOR > 98%) is the major goal. 5-ALA fluorescence
and iMRI are the two most efficient approaches to achieve a GTR. However, iMRI, in
particular, is not yet established because of its poor cost-benefit ratio if only
used intraoperatively. Therefore, we analyzed our dual-use iMRI suite concerning results
of surgical resection, histopathologic accuracy, and SSI in GBM cases.
In our study, 85.29% of the Gd-enhancing GBMs showed a strong 5-ALA fluorescence intraoperatively.
This finding supports the hypothesis that not only a disrupted blood-brain barrier
is responsible for the fluorescence. The decreased activity of the enzyme ferrochelatase
seems to play an important role.[21] However, in 11 cases we did not use 5-ALA because of contraindications concerning
other drugs, elevated liver enzymes, or brain metastases suspected preoperatively.
GTR was achieved in 74.68% of all GBM cases. This corresponds to results by Roder
et al,[22] who compared GTR in three different groups. The rate of GTR in their iMRI group
was 74%, in the 5-ALA group 46%, and in the white-light group 28%. Other studies made
a preoperative selection as to whether GTR could be achieved, resulting in a GTR rate
of 96% with high-field iMRI-guided resections in non-eloquent tumor locations.[23] A larger study consisting of 139 patients showed a rate of GTR with 5-ALA-guided
resections of 65%.[24] Our GTR rate of 74.68% achieved by 5-ALA and iMRI is relatively high considering
that the rate of tumors located in eloquent areas was 45.57% and that we did not select
for the ability to achieve GTR. Therefore, we assume there is a synergistic effect
of the combination of iMRI and 5-ALA. The latter is an operator-dependent visualization
procedure. Some areas of the tumor can be covered by blood or cotton patties. Those
“invisible” tumor remnants can be detected by an operator-independent imaging like
iMRI.
In 52.54% of our patients we achieved a GTR only after using iMRI, which demonstrates
its importance. The rate of GTR was significantly higher after iMRI-guided additional
resections compared with previously reported GTRs without 5-ALA and iMRI and with
5-ALA, but without iMRI. However, a comparison with other studies is limited. GTR
is often not defined in the same way.
Mean EOR was 96.27% in our patient collective. EOR > 98% is known as a significant
predictor for prolonged survival of GBM patients.[1]
[2] Studies of 92 GBM patients showed that an EOR of 100% is related with a survival
of 93 weeks, whereas survival decreases to 88.5 weeks if the EOR is between 75% and
99% and to 62.9 weeks, if the EOR is between 50% and 74%.[25]
In 69.6% of the GBM patients in our study, additional resections were performed after
iMRI. The PPV that the Gd-enhancing tissue detected by iMRI was astrocytic tumor,
was 88.6%. Another study showed a PPV of 64.3% for presence of tumor tissue after
iMRI-guided resections and of 96% for 5-ALA-guided resection.[26] This study however, was conducted with a low-field MRI. Therefore, PPV of iMRI in
our study is higher than that of the low-field iMRI, but still lower than the PPV
of 5-ALA. In general, it should be considered that the PPV is influenced by scar tissue
in recurrent GBM and by surgical manipulation, so-called surgically induced enhancement.
Sensitivity was 100% and specificity 70.6%. Coburger et al[27] reported a sensitivity of 41% and also a specificity of 70%. It is difficult to
compare the sensitivity of our study with the sensitivity in the study of Coburger
et al, because these authors calculated the sensitivity by only considering World
Health Organization grade IV tissue. . The sensitivity of 100% and the specificity
of 70% in our study point to the risk of over diagnosing of tumor by iMRI. This phenomenon
again might be linked to the fact that 28 (35.44%) of our 79 patients had a recurrent
GBM with scar tissue, and that also 8 patients (10.8%) had a secondary GBM. Therefore,
previous surgical or radiotherapeutic treatments have to be considered when interpreting
iiMRI scans. The inclusion of those patients may be a limitation of our study, but
on the other hand, inclusion of these patients represents a real life setting. Intraoperative
magnetic resonance spectroscopy or perfusion-weighted MRI seem to be reasonable methods
to reduce the problem of overdiagnosing.
Long-lasting procedures represent important risk factors for SSI. The prolongation
of the surgery by iMRI and the fact that our MRI scanner is used for both diagnostic
and intraoperative imaging made it necessary to examine the safety of our procedure.
The mean iMRI scan time was 33.6 minutes. Including the transport and positioning
of the patient, 55 minutes need to be scheduled. Indeed, the relative risk of operations
lasting 2 hours causing infections is 12.6 and for those > 3 hours is 24.3. These
data were observed in 726 craniotomies and 663 spinal operations.[28] However, duration of surgery was not a statistically significant variable in our
analysis of possible risk factors for SSI.
Four SSIs were observed in 79 GBM operations in which iMRI was performed. Our SSI
rate of 5.06% is within the normal range of neurosurgical procedures. The SSI rate
in a collective of 1,007 patients with intracranial procedures performed without iMRI
in our department was 5.45%. The SSI rate in the group of recurrent gliomas with prior
surgery, chemotherapy, and radiation therapy was 7.14%. Therefore, the dual usage
of the MRI scanner has not increased our SSI rate. Larger collectives composed of
1,181 and 3,042 patients showed SSI rates of 3.47% and 3.68%, respectively. Some studies
reported meningitis despite antibiotic prophylaxis in 1.63% of all cases.[29] Fortunately, meningitis was not observed in our study. The causative agents of the
SSIs in our study, included two cutaneous (one Staphylococcus epidermidis and one S. aureus), and two noncutaneous bacteria (Enterobacter cloacae and Pseudomonas aeruginosa). Cocci are responsible for 70.6% of all superficial and 64.5% of all deep SSIs.[30] In addition to the decrease in infections caused by cutaneous bacteria, the frequent
use of first-generation cephalosporins will likely increase SSIs caused by gram-negative
bacteria.[29]
In our collective of the 29 patients in whom we also administered vancomycin and gentamicin
intrathecally, an SSI rate of 0% was observed. In contrast, our cephalosporin-only
group of 50 patients had an SSI rate of 8%. However, that difference was not statistically
significant. Other retrospective studies also claimed that the use of additional intrathecal
antibiotic prophylaxis could be advantageous. Ragel et al[18] determined the rate of SSIs with vancomycin combined with gentamicin to be 0.4%,
with gentamicin 5.4%, and with standardized preoperative single-shot antibiotic prophylaxis
6.6%. Taken these data and our findings into consideration, intrathecal antibiotic
prophylaxis should be examined in future studies.[18]
Up to now iMRI is not universally established in neurosurgical departments because
of the poor cost-benefit ratio if installed only for intraoperative use. Between July
2011 and June 2015, we performed 17,000 MRI scans for diagnostic use in addition to
250 intraoperative resection controls. Two to three iiMRI scans, ∼ 40 diagnostic MRI
scans for inpatients and 35 diagnostic scans for ambulatory patients were performed
per week, allowing to use the iMRI economically.
Conclusion
There is obvious improved surgical success if iMRI together with 5-ALA are used. In
particular, EOR was considerably higher in spite of the many GBMs located in eloquent
areas. Intraoperative Gd-enhancement is indicative of residual tumor and, therefore,
can guide additional resections. Despite the dual use of our iMRI suite, the rate
of SSIs was within the normal range for neurosurgical procedures. Consequently, sharing
a high-field MRI for daily diagnostic use and intraoperative resection control is
a safe and successful concept.
