Theodoros Kombos

Navigated transcranial magnetic stimulation for preoperative functional diagnostics in brain tumor surgery.

OBJECTIVE Transcranial magnetic stimulation (TMS) is a noninvasive method for analyzing cortical function. To utilize TMS for presurgical functional diagnostics, the magnetic impulse must be precisely targeted by stereotactically positioning the coil. The aim of this study was to evaluate the usefulness of TMS for operation planning when combined with a sensor-based electromagnetic navigation system (nTMS). METHODS Preoperative functional mapping with nTMS was performed in 10 patients with rolandic tumors. Intraoperative mapping was performed with the “gold standard” of direct cortical stimulation. Stimulation was performed in the same predefined 5-mm raster for both modalities, and the results were compared. RESULTS In regard to the 5-mm mapping raster, the centers of gravity of nTMS and direct cortical stimulation were located at the same spot in 4 cases and at neighboring spots in the remaining 6 cases. The mean distance between the tumor and the nearest motor response (“safety margin”) was 7.9 mm (range, 5–15 mm; standard deviation, 3.2 mm) for nTMS and 6.6 mm (range, 0–12 mm; standard deviation, 3.4 mm) for direct cortical stimulation. CONCLUSION nTMS allowed for reliable, precise application of the magnetic impulse, and the peritumoral somatotopy corresponded well between the 2 modalities in all 10 cases. nTMS is a promising method for preoperative functional mapping in motor cortex tumor surgery.

Multimodal protocol for awake craniotomy in language cortex tumour surgery

SummaryBackground. Intra-operative neurophysiological language mapping has become an established procedure in patients operated on for tumours in the area of the language cortex. Awake cranial surgery has specific risks and patients are exposed to an increased physical and mental stress. The aim of the study was to establish an algorithm that enables tailoring the neurosurgical and anaesthetic techniques to the individual patient. Method. A total of 25 patients underwent awake craniotomy for intra-operative language mapping between 1999 and 2004. Following craniotomy under analgesia and sedation without rigid pin fixation of the head, cortical language mapping was performed in the fully co-operative patient. The results of functional magnetic resonance imaging and of cortical language mapping were incorporated into the 3D dataset for neuronavigation. Depending on the functional data and the individual operative risk tumour resection then proceeded either under conscious sedation with the option of subcortical language monitoring or under general anaesthesia. Findings. After cortical language mapping patients are assigned to one of four groups: BACC (Berlin awake craniotomy criteria) I–IV. BACC I (9 patients): adequate functional data + operative risk not increased ⇒ tumour resection in the awake patient; BACC II (4 patients): limited functional data + operative risk not increased ⇒ tumour resection in the awake patient with the option of language monitoring as needed; BACC III (9 patients): adequate functional data + increased operative risk ⇒ tumour resection under general anaesthesia using functional navigation; BACC IV (3 patients): limited functional data + increased operative risk ⇒ tumour resection in the awake patient with the option of language monitoring as needed. We observed less adverse events in group BACC III. No permanent deterioration of language function occurred in this series. Conclusions. The multimodal protocol for awake craniotomy provides for tumour resection under general anaesthesia in selected patients using functional neuronavigation. Our experience with the algorithm suggests that it is a useful tool for preserving function in patients undergoing surgery of the language cortex while reducing the operative risk on an individual basis.

Impact of Intraoperative Neurophysiological Monitoring on Surgery of High-Grade Gliomas

Introduction: Controversy exists on the application of intraoperative monitoring (IOM) procedures during malignant glioma surgery. Because resection rate correlates with the survival rate, it is of paramount importance to determine these values. This study evaluates the impact of IOM on the resection rates, the survival rate, the quality of life, and the functional outcome of malignant gliomas. Methods: Forty patients with a glioma were included in the study. They were divided into two groups: group 1, patients with a glioma not adjacent to motor cortical areas operated without the use of IOM, and group 2, patients with a glioma adjacent to the central region operated under IOM. The further treatment was the same in both groups. The following parameters were analyzed: tumor resection rate, survival rate, preoperative and postoperative Karnowsky Performance Score, and preoperative and postoperative motor function. Results: There were no statistically significant differences in the type of surgery performed or in the resection grade in both groups. No statistically significant difference was found in the median survival of the two groups in the Kaplan-Meier analysis with mean survival time 48.8 and 48.2 weeks. The mean Karnowsky Performance Score preoperative was 82.5 and 81.5, and 81.1 and 82.7 after 6 months, for groups 1 and 2, respectively. Conclusion: The data presented here demonstrate that tumor resection is not negatively influenced by IOM. Accordingly, gliomas that are found to be otherwise resectable should not be excluded from aggressive management simply because of their vicinity to the motor cortex. Surgery should be performed under IOM.

Intraoperative electrocortical stimulation of Brodman area 4: a 10-year analysis of 255 cases.

BackgroundBrain tumor surgery is limited by the risk of postoperative neurological deficits. Intraoperative neurophysiological examination techniques, which are based on the electrical excitability of the human brain cortex, are thus still indispensable for surgery in eloquent areas such as the primary motor cortex (Brodman Area 4).MethodsThis study analyzed the data obtained from a total of 255 cerebral interventions for lesions with direct contact to (121) or immediately adjacent to (134) Brodman Area 4 in order to optimize stimulation parameters and to search for direct correlation between intraoperative potential changes and specific surgical maneuvers when using monopolar cortex stimulation (MCS) for electrocortical mapping and continuous intraoperative neurophysiological monitoring.ResultsCompound muscle action potentials (CMAPs) were recorded from the thenar muscles and forearm flexors in accordance with the large representational area of the hand and forearm in Brodman Area 4. By optimizing the stimulation parameters in two steps (step 1: stimulation frequency and step 2: train sequence) MCS was successful in 91% (232/255) of the cases. Statistical analysis of the parameters latency, potential width and amplitude showed spontaneous latency prolongations and abrupt amplitude reductions as a reliable warning signal for direct involvement of the motor cortex or motor pathways.ConclusionMCS must be considered a stimulation technique that enables reliable qualitative analysis of the recorded potentials, which may thus be regarded as directly predictive. Nevertheless, like other intraoperative neurophysiological examination techniques, MCS has technical, anatomical and neurophysiological limitations. A variety of surgical and non-surgical influences can be reason for false positive or false negative measurements.

Subcortical mapping and monitoring during insular tumor surgery.

OBJECT The treatment of insular tumors is controversial. Surgical treatment is associated with a higher morbidity rate than other therapies. The present work presents a new method in which the descending motor pathways are monitored during surgery for insular tumors. METHODS Intraoperative monitoring was performed in a combination of 2 techniques. The motor cortex was stimulated with a transcranial electrical stimulus. In addition, direct subcortical stimulation was performed with an electrical anodal monopolar stimulus. Compound motor action potentials (CMAPs) were recorded from target muscles. RESULTS Fifteen patients were included in this preliminary study. Following transcranial stimulation, CMAPs were recorded in all cases. Subcortical stimulation was successful in 12 cases. Significant CMAP alterations were recorded in 5 patients. There were no false-negative results in the series. CONCLUSIONS The technique presented here is a safe method. It allows a quantitative monitoring of motor function and functional mapping of the pyramidal tract during insular surgery.

Neurophysiological basis of direct cortical stimulation and applied neuroanatomy of the motor cortex: a review

Intraoperative electrical stimulation of the motor cortex is a sensitive method for intraoperative mapping and monitoring of this region. Two different stimulation techniques have been established, the bipolar and monopolar techniques. Controversy exists regarding the most suitable method. Both methods have advantages and disadvantages and different electrophysiological backgrounds. The present study is a review of the electrophysiological basis of direct cortical electrical stimulation of the motor cortex. Both methods are discussed and their field of application is presented.

Impact of somatosensory evoked potential monitoring on cervical surgery.

Summary Controversy still exists about the necessity of somatosensory evoked potential (SSEP) monitoring during cervical surgery. The purpose of this prospective study is to determine the impact of SSEP monitoring on anterior cervical surgery. Intraoperative SSEP monitoring was performed in 100 patients treated by an anterior cervical approach. The patients were divided into three groups according to their preoperative clinical condition. Somatosensory evoked potential monitoring was performed during five stages of the procedure: M1, after the induction of anesthesia; M2, during positioning; M3, during distraction of the intervertebral space; M4, throughout decompression; and M5, during graft placement. Normal SSEPs were obtained during M1 from all the patients in group 2. Pathologic SSEPs were recorded at M1 in 45 patients from group 1. No SSEPs were recorded at M1 in six patients in group 3. A deterioration of the SSEPs was observed in 35 patients during M2. Deteriorated SSEPs were observed during M3 in 14 patients. No deterioration of the SSEPs was recorded during M4. Intraoperative SSEP monitoring is easy to perform and helps to increase safety during anterior cervical surgery. Critical phases of the surgical procedure were identified and the surgical strategy was modified as a result of this study.

Does preoperative paresis influence intraoperative monitoring of the motor cortex

Summary Intraoperative monitoring of motor function by means of motor evoked potentials (MEPs) is a new method. The current study examines the influence of preoperative paresis on the feasibility and reliability of this method. Intraoperative monitoring of MEPs was performed in 58 patients during surgery in the central region. The patients were divided into three groups according to their preoperative strength (group I, muscle strength less than or equal to grade 4 according to the British Medical Research Council grading system [n = 17]; group II, normal strength (n = 36); and group III, muscle strength less than grade 5 but not worse than grade 4 [n = 5]). The motor cortex was stimulated directly with a high-frequency monopolar anodal train. In groups II and III, MEPs were elicited in all patients on cortical stimulation, whereas in group I a response was obtained in only 88% of patients. The MEP parameters in all groups had a broad interindividual range of variation. A correlation between individual intraoperative potential changes and surgical maneuvers was observed in seven patients in group II and in four patients in group I. No MEP changes were recorded in group III. Irreversible MEP changes (groups I and II) resulted in postoperative clinical deterioration. No postoperative deterioration of motor function was observed in patients with reversible MEP changes. Preoperative paresis reduces the feasibility of the method; however, it has no influence on the intraoperative pattern and reaction of the MEPs.

Functional Magnetic Resonance Imaging and Cortical Mapping in Motor Cortex Tumor Surgery: Complementary Methods

Functional magnetic resonance imaging (fMRI) and direct electrocortical stimulation (DES) are the most commonly used means of analyzing the functional brain topography prior to surgery in the vicinity of Brodmann area 4. No consensus has been established in the literature about the significance of both procedures in reducing operative morbidity. The study presented here was conducted in 30 patients with tumors in the area of the primary motor cortex. Blood oxygen level dependent (BOLD) sequences were preoperatively established with a standardized paradigm. Intraoperatively motor mapping was performed with DES. The results of both methods were digitally matched with a frameless image-guidance system. Correlations between the results of fMRI and of DES were analyzed. Furthermore, the potential influences of the size, position, and histology of the lesions on the mapping results were analyzed and the motor outcome was evaluated. The mean deviation between the results of fMRI and of DES was 13.8 mm (range: 7-28 mm). This deviation was independent of the histology, size, or location of the corresponding lesion. The individual variability of the analysis threshold value for the evaluation of the BOLD sequences led to a considerable topographical inaccuracy. As complementary methods, fMRI contributes to estimating the operational risk, while DES is performed when the results of MRI and fMRI suggest an immediate proximity of the tumor to motor areas.

Neuronavigation without rigid pin fixation of the head in left frontotemporal tumor surgery with intraoperative speech mapping.

OBJECTIVE Intraoperative speech mapping has evolved into the “gold standard” for neurosurgical removal of lesions near the language cortex. The integration of neuronavigation into a multimodal protocol can improve the reliability of this type of operation, but most systems require rigid fixation of the patients head throughout the operation. This article describes and evaluates a new noninvasively attached sensor-based reference tool, which can replace rigid pin fixation of the patients head during awake craniotomies. METHODS The attachment technique and the resulting application accuracy were investigated under clinical conditions in 13 patients undergoing awake craniotomy with intraoperative mapping of cortical language sites. RESULTS Spatial information was used for updating the image guidance by continuously adjusting the image planes relative to the position of the patients head. The mean registration error achieved with this technique was 1.53 ± 0.51 mm (fiducial registration error ± standard deviation). The systems median application accuracy between dura opening and closure ranged from 0.83 to 1.85 mm (position error). CONCLUSION The use of a reference sensor can replace uncomfortable pin fixation of the patients head during navigation-supported awake craniotomies. Application accuracy is not affected by repositioning of the patient or by unavoidable head movements. Thus, this technique enables full exploitation of the benefits of navigation in a multimodal operative protocol without the need to rigidly fix the patients head.