Marie-Therese Forster

Navigated transcranial magnetic stimulation and functional magnetic resonance imaging: advanced adjuncts in preoperative planning for central region tumors.

BACKGROUND:Tumor resection in the vicinity of the motor cortex poses a challenge to all neurosurgeons. For preoperative assessment of eloquent cortical areas, functional magnetic resonance imaging (fMRI) is used, whereas intraoperatively, direct cortical stimulation (DCS) is performed. Navigated transcranial magnetic stimulation (nTMS) is comparable to DCS in activating cortical pyramidal neurons. OBJECTIVE:To evaluate the reliability of nTMS compared with fMRI and DCS for preoperative resection planning of centrally located tumors. METHODS:In a prospective series, 11 patients (ages, 20-63 years; mean, 41.9 ± 14.9 years, 2 women) with tumors located in or adjacent to the motor cortex were evaluated for surgery. fMRI and nTMS were applied for preoperative assessment of the extent of tumor resection. A 3-dimensional anatomic data set with superimposed fMRI data was integrated in the eXimia Navigated Brain Stimulation station for ensuing motor cortex mapping by nTMS. Responses from nTMS were evaluated by electromyographic response. During surgery, the coordinates of each DCS site were unambiguously defined and integrated into neuronavigation. A post hoc comparison of the coordinates of nTMS, fMRI, and DCS was performed. RESULTS:Distances from nTMS to DCS (10.5 ± 5.67 mm) were significantly smaller than those from fMRI to DCS (15.0 ± 7.6 mm). CONCLUSION:nTMS anticipates information usually only enabled by DCS and therefore allows surgical planning in eloquent cortex surgery.

The influence of preoperative anticoagulation on outcome and quality of life after surgical treatment of chronic subdural hematoma

The main aim of this study was to investigate the influence of perioperative anticoagulation on the clinical course and outcome of 144 patients who underwent surgery for chronic subdural hematoma (CSDH). The outcome was categorized according to the modified Rankin Scale (mRS), Barthel Index and postoperative quality of life (QoL) scale. There was a significant correlation between preoperative aspirin medication and reoperation (Mann-Whitney U-test, p<0.05). Moreover, dosage and duration of postoperative low-molecular-weight heparin (LMWH) administration were associated with a higher risk of reoperation (Mann-Whitney U-test, p<0.01) and a worse outcome on the mRS (Mann-Whitney U-test, p<0.05). Intraoperative treatment with prothrombin complex concentrate led to a poor outcome on the mRS (Craddock-Flood test, p<0.05). Reoperation is the strongest predictive factor of a poor QoL after surgical treatment of CSDH. Both preoperative and postoperative anticoagulation treatment may affect reoperation rate and, thus, postoperative QoL.

Intra-operative subcortical electrical stimulation: A comparison of two methods

OBJECTIVE For intra-operative subcortical electrical stimulation of the corticospinal tract, two techniques - originally described for cortical stimulation - have evolved: the 50-Hz-stimulation first described by Penfield in 1937 and the high-frequency multipulse train stimulation technique first described by Taniguchi in 1993. Motor thresholds of both methods in combination with a bipolar and monopolar stimulation technique and their reliability for eliciting motor evoked potentials (MEPs) were studied. METHODS Data were obtained in 20 patients (50±17 years; 10 females) undergoing tumour resection under general anaesthesia. Both 50-Hz-stimulation of 1-s duration and a multipulse stimulation (5 pulses interstimulus interval 4 ms, 0.5-Hz repetition rate) were applied with a bipolar probe (1.5-mm ball tip, 8-mm interelectrode distance) and a monopolar probe (1.5-mm-diameter tip). MEPs were recorded in muscles contralateral to the stimulated hemisphere. Comparison of different stimulation modalities was performed at the site where monopolar multipulse stimulation technique elicited MEPs with the lowest stimulation intensity (constant current monophasic cathodal stimulation, individual pulse width 0.5 ms, max. 25 mA). RESULTS MEPs were elicited by monopolar multipulse stimulation with an intensity of 8±3.9 mA (21/21 stimulation sites); monopolar 50-Hz stimulation with 12±5.4 mA (18/21 stimulation sites); bipolar multipulse stimulation with 14±8.1 mA (12/21 stimulation sites) and bipolar 50-Hz stimulation with 15±6.3 mA (11/21 stimulation sites). CONCLUSIONS Stimulation intensities for eliciting MEPs are significantly lowest for the monopolar multipulse stimulation (p<0.025). Monopolar compared to bipolar stimulation resulted in eliciting MEPs in a higher number of tested patients (Fishers p<0.0001). SIGNIFICANCE Subcortical stimulation with a monopolar probe and a multipulse stimulation is most efficient for the purpose of identifying the corticospinal tract. This is explained by the more radiant electric field properties of the monopolar probe compared to the bipolar probe.

Management and outcome of patients with acute traumatic subdural hematomas and pre-injury oral anticoagulation therapy

Abstract Background: Acute subdural hematomas (aSDHs) are found in up to one-third of patients with severe traumatic brain injury and are associated with an unfavorable outcome in the majority of cases. Mortality ranges between 40 and 60%, but was reported to be even higher in patients undergoing oral anticoagulation therapy (OAT) at the time of injury. The objective of this study is to specifically report on the peri-operative management and outcome of patients with aSDH and pre-injury OAT. Material and Methods: From June 2002 to June 2006, all patients with OAT who underwent surgical treatment of aSDH were retrospectively analysed. Results of pre-operative blood tests, the peri-operative and surgical management and the clinical courses were assessed. Patient outcome is reported according to the Glasgow Outcome Scale (GOS) at 6 months. Results: Eleven (10.3%) out of 107 patients with aSDH were on OAT. Patients with OAT were significantly older than patients without OAT (72.4 ± 9.3 versus 59.9 ± 17.5 years; p<0.05, Mann–Whitney U-test). Intensity of head trauma was moderate in four and severe in seven patients with a median pre-operative Glasgow Coma Scale (GCS) of 8. Median pre-treatment prothrombin time and international normalized ratio were 23% (range: 10–65%) and 3.3 (range: 1.5–10.6), respectively. Replacement therapy consisted of administration of prothrombin complex concentrates, vitamin K and FFP (fresh frozen plasma). In four patients, antithrombin was additionally given to prevent disseminated intravascular coagulation. Surgical treatment consisted of craniotomy (n=10) or craniectomy (n=1) and hematoma evacuation with intracranial pressure probe placement. Low molecular weight heparin was administered as pharmacological prophylaxis of thrombembolic events in an increasing dose post-operatively. At 6 months, six out of 11 patients survived with a median GOS of 4. All-cause mortality was 45.5%. A pre-operative GCS of ≤ 8 was not associated with an increased risk of mortality (p>0.5, Fishers exact test). No relevant rebleedings or thrombembolic complications were observed. The mortality rate of patients who did not undergo OAT was 50%. Conclusion: A large number of patients with aSDH are on pre-injury OAT. Specific replacement therapy facilitates successful clot evacuation without bleeding complications. The overall outcome of these patients does not seem to differ from historical cohorts with aSDH without OAT, but a large prospective multicenter study is warranted to answer that question.

Test-retest Reliability of Navigated Transcranial Magnetic Stimulation of the Motor Cortex

BACKGROUND: Because navigated transcranial magnetic stimulation (nTMS) is increasingly used in neurosurgical research, interpretation of its results is of utmost importance. OBJECTIVE: To evaluate the test-retest reliability of nTMS. METHODS: Twelve healthy participants underwent nTMS at 2 different sessions separated by 10.3 ± 9.6 days. Investigated parameters included resting motor thresholds, hotspots, and centers of gravity calculated for the first dorsal interosseous, abductor pollicis brevis, extensor digitorum, tibial anterior, and abductor hallucis muscles. RESULTS: Excellent reliability of resting motor thresholds was observed. Hotspots and centers of gravity showed moderate to excellent repeatability along the anteroposterior axis (intraclass correlation coefficient, 0.54-0.89), whereas the x coordinate presented mainly poor to moderate stability (intraclass correlation coefficient, 0.11-0.89). Movement of centers of gravity over sessions was 0.57 ± 0.32 cm, and hotspots laid 0.79 ± 0.47 cm apart. Calculation of coefficient of variation revealed high reliability of investigated parameters in upper extremities; in lower extremity muscles, high variation across sessions was observed. CONCLUSION: nTMS can be considered a reliable tool, thus opening new fields of noninvasive investigations in neurosurgery. The results presented here should be considered in the interpretation of individual nTMS results. ABBREVIATIONS: CoG, center of gravity FDI, first dorsal interosseous ICC, intraclass correlation coefficient MEP, motor evoked potential nTMS, navigated transcranial magnetic stimulation RMT, resting motor threshold TA, tibial anterior TMS, transcranial magnetic stimulation

Does navigated transcranial stimulation increase the accuracy of tractography? A prospective clinical trial based on intraoperative motor evoked potential monitoring during deep brain stimulation.

BACKGROUND Tractography based on diffusion tensor imaging has become a popular tool for delineating white matter tracts for neurosurgical procedures. OBJECTIVE To explore whether navigated transcranial magnetic stimulation (nTMS) might increase the accuracy of fiber tracking. METHODS Tractography was performed according to both anatomic delineation of the motor cortex (n = 14) and nTMS results (n = 9). After implantation of the definitive electrode, stimulation via the electrode was performed, defining a stimulation threshold for eliciting motor evoked potentials recorded during deep brain stimulation surgery. Others have shown that of arm and leg muscles. This threshold was correlated with the shortest distance between the active electrode contact and both fiber tracks. Results were evaluated by correlation to motor evoked potential monitoring during deep brain stimulation, a surgical procedure causing hardly any brain shift. RESULTS Distances to fiber tracks clearly correlated with motor evoked potential thresholds. Tracks based on nTMS had a higher predictive value than tracks based on anatomic motor cortex definition (P < .001 and P = .005, respectively). However, target site, hemisphere, and active electrode contact did not influence this correlation. CONCLUSION The implementation of tractography based on nTMS increases the accuracy of fiber tracking. Moreover, this combination of methods has the potential to become a supplemental tool for guiding electrode implantation.

Combination of Intraoperative Magnetic Resonance Imaging and Intraoperative Fluorescence to Enhance the Resection of Contrast Enhancing Gliomas.

BACKGROUND Evidence suggests that extent of resection (EOR) is a prognostic factor for patients harboring gliomas. Recent studies have displayed the importance of intraoperative magnetic resonance imaging (iMRI) with 5-aminolevulinic acid (5-ALA) fluorescence-guidance in order to maximize EOR. OBJECTIVE To compare iMRI and 5-ALA fluorescence-guidance and the impact on patient survival. METHODS Thirty-two patients with contrast-enhancing gliomas undergoing intended gross total resection (GTR) were included in a prospective study. Surgeries were started under white-light conditions. When GTR was thought to be achieved, an iMRI scan was performed and a blue light turned on to search for unintentionally remaining tumor tissue. iMRI findings were compared with intraoperative fluorescence findings. Histological examination of tumor bulk and any additionally resected tissue was performed. All patients underwent early postoperative high-field MRI to determine EOR. RESULTS In 13 patients (40.6%), iMRI and fluorescence unequivocally did not show residual tumor intraoperatively. In 19 patients (59.4%), resection was continued due to iMRI or fluorescence findings. In 9 of these (47.4%), iMRI and fluorescence findings were inconsistent regarding residual tumor. GTR according to postoperative MRI was achieved in all but 1 patient. Histological examination ruled out false positive findings in all additionally resected specimens. Sensitivity and specificity to detect residual tumor tissue were 75% and 100%, respectively, for iMRI and 70% and 100% for 5-ALA fluorescence. CONCLUSION Use of iMRI as well as fluorescence-guidance are appropriate methods to improve the extent of resection in surgery of contrast-enhancing gliomas. Best results can be achieved by complementary use of both modalities.

Spinal cord tumor surgery--importance of continuous intraoperative neurophysiological monitoring after tumor resection.

Study Design. A retrospective clinical analysis of patients operated on for spinal tumors. Objective. To report on the importance of intraoperative neurophysiological monitoring (INM) throughout the entire surgical procedure. Summary of Background Data. Postoperative neurological deterioration, despite unaltered neurophysiological monitoring, has been reported. This might be related to timely restricted monitoring. Thus, the likelihood of alterations in INM from positioning to wound closure was analyzed. Methods. Two hundred three patients (age range, 54.9 ± 17.4 yr) undergoing intradural tumor removal were sampled in a prospective database and analyzed for the occurrence of alterations in intraoperative somatosensory- and motor-evoked potentials. Results. INM alterations were observed in 47 of 203 (23.2%) patients. These alterations were related to tumor resection in 29 (14.3%) cases, whereas these were unrelated to tumor removal in 18 patients: laminotomy in 5 (2.5%) patients, dura opening in 7 (3.5%) patients, dura closure in 5 (2.5%) patients, and laminoplasty in 1 (0.5%) patient caused INM changes. Conclusion. This study demonstrates that monitoring beyond tumor resection is of essential importance in order to detect all critical phases of surgical procedure and to counteract accordingly.

Combination of 5-ALA and iMRI in re-resection of recurrent glioblastoma

Abstract Background Tumour resection plays a role in the initial treatment but also in the setting of recurrent glioblastoma (rGBM). To achieve maximum resection, 5-aminolevulinic acid (5-ALA) and intraoperative MRI (iMRI) are used as surgical tools. Aiming at complete tumour re-resection, we started combining iMRI with 5-ALA to find out if this leads to better surgical results. Methods We performed tumour resections in seven patients with rGBM, combining 5-ALA (20 mg/kg bodyweight) with iMRI (0.15 T). Radiologically complete resections were intended in all seven patients. We assessed intraoperative fluorescence findings and compared these with intraoperative imaging. All patients had early postoperative MRI (3 T) to verify final iMRI scans and received adjuvant treatment according to interdisciplinary tumour board decision. Results Median patient age was 63 years. Median KPS score was 90, and median tumour volume was 8.2 cm3. In six of seven patients (85%), 5-ALA induced fluorescence of tumour-tissue was detected intraoperatively. All tumours were good to visualise with iMRI and contrast media. One patient received additional resection of residual contrast enhancing tissue on intraoperative imaging, which did not show fluorescence. Radiologically complete resections according to early postoperative MRI were achieved in all patients. Median survival since second surgery was 7.6 months and overall survival since diagnosis was 27.8 months. Conclusions 5-ALA and iMRI are important surgical tools to maximise tumour resection also in rGBM. However, not all rGBMs exhibit fluorescence after 5-ALA administration. We propose the combined use of 5-ALA and iMRI in the surgery of rGBM.

Sphenoorbital meningiomas: surgical management and outcome

Abstract Objective: Surgical management of sphenoorbital meningiomas ranges among the most complex of intracranial tumors. We report on our experience of surgical technique, outcome, and tumor recurrence in sphenoorbital meningiomas. Methods: Between 2003 and 2013, surgical resections for sphenoorbital meningioma were performed in 18 patients (aged 49·6±9·8 years, only women), with two patients operated anew due to tumor recurrence. Results: Main symptom was proptosis (83·3%), followed by diminished visual acuity (38·9%), and dizziness (11·1%). In all patients the lateral orbital wall was resected, whereas the orbital roof and the zygoma were removed according to the extent of their tumorous infiltration. Unroofing of the optic canal was performed in 10 cases (55·6%) and unroofing of the optic foramen in two (11·1%). For reconstruction split calvarian bone and titanium mesh were used in six (33·3%) and seven patients (38·9%), respectively; in one patient both techniques were applied. In five patients (27·8%), no reconstruction was necessary. Complete tumor resection (Simpson grade 1 and 2) was achieved in 14 cases (77·7%). Postoperatively, proptosis improved in all patients. Median follow-up was 39·5±33·3 months (range 1–105) in 16 patients; 2 patients were lost to follow-up. No tumor recurrence was noted in five (27·8%) patients, whereas in nine (50%) patients tumor remnants proved stable over time. Two (11·1%) patients experienced progression of residual tumor, resulting in reoperation after 27 and 109 months, respectively. Discussion: Despite their delicate anatomical relations, surgery of sphenoorbital meningiomas is safe when combining modern techniques.