Impact of Brain Shift on Intraoperative Neurophysiological Monitoring with Cortical Strip Electrodes

Summary.  Background: Intraoperative neurophysiological monitoring has become the standard procedure for locating eloquent regions of the brain. Such continuous electrical stimulation of motor pathways is usually applied by means of flat silicon-embedded electrodes placed directly on the motor cortex. However, shifting of the silicon strip on the cortical surface as well as electrode displacement due to brain shift underneath the electrode can lead to inaccurate recordings not directly caused by intraoperative impairment of the motor cortex or the motor pathways.  Method: This prospective study was conducted to quantify cortical brain shift during open cranial surgery and to assess its impact on electrode positioning in 31 procedures near the precentral gyrus. Three groups of different lesion volumes were distinguished. Movement of the cortex between opening of the dura and completion of tumor removal as well as cortical electrode shifting were digitally measured and analyzed.  Findings: Cortical surface structures evidenced a significantly larger shift (up to 23.4 mm) in comparison to the electrode strips (up to 4.2 mm) in lesions with a volume of over 20 ml. Cortex shifting highly correlated with lesion volume, whereas strip electrode movement was almost unidirectional and did not differ significantly among the three groups. However, the way they were placed (completely on the cortex vs. partly underlying or overlapping the craniotomy borders) affected the magnitude of their intraoperative displacement. As a consequence, 3 of the 31 cases (9.3%) showed a significant change in the recorded motor responses due to intraoperative dislocation of the stimulating electrode.  Interpretation: Changes in the location of cerebral structures due to intraoperative brain shift may exert a marked influence on intraoperative neurophysiological monitoring if cortical strip electrodes are used. Therefore, long-term monitoring of the central region requires continuous checking of the position of stimulating electrodes and, if necessary, correction of their location. Published online December 5, 2002 Acknowledgments  The authors thank Mr. Udo Warschewske and his co-workers of Functional Imaging Technologies (Waltersdorf, Land Brandenburg, Germany) for their help in establishing the software necessary for the navigation-controlled calculation of intraoperative brain and electrode shifting.  Correspondence: Dr. med. Olaf Suess, Department of Neurosurgery, Benjamin Franklin University Hospital, Free University of Berlin, Hindenburgdamm 30, 12200 Berlin, Germany.     

Demonstration of Cerebral Plasticity by Intra-Operative Neurophysiological Monitoring: Report of an Uncommon Case

Summary  It has been postulated long ago that “eloquent” areas shift their location in patients with arteriovenous malformations (AVM). Obviously the “motor region” in not located in the precentral gyrus in a patient with an AVM in the “motor region”.  We report on the case of a 15-year old boy with an AVM in the left sensorimotor cortex, in whom intra-operative mapping showed an inexcitability of the precentral gyrus, while stimulation of the cortex anterior to the primary motor cortex elicited motor responses. This indicates that motor function was translocated from the primary to the supplementary motor cortex. Surgery was performed under general anaesthesia. Neurophysiological monitoring was performed throughout surgery. The central sulcus was identified by phase reversal of the somatosensory evoked potentials. The motor cortex was mapped by direct high-frequency (500 Hz) monopolar anodal stimulation.  In the patient herein reported, stimulation of the “anatomically” defined primary motor cortex induced no motor response, as expected. Motor response was elicited only by stimulation of the cortex anterior to the precentral gyrus. There was no postoperative deterioration of motor function. These observations indicate that the precentral gyrus was functionally “useless”. The motor region was relocated into more rostral areas in the supplementary motor cortex. This translocation of function in the presence of an AVM indicates cerebral plasticity.     

Intraoperative Vagus Nerve Monitoring: A Transnasal Technique during Skull Base Surgery

Objectives Intraoperative vagus nerve monitoring during skull base surgery has been reported with the use of an oral nerve monitoring endotracheal tube. However, the intraoral presence of an endotracheal tube can limit exposure by its location in the operative field during transfacial approaches and by limiting superior mobilization of the mandible during transcervical approaches. We describe a transnasal vagus nerve monitoring technique. Design and Participants Ten patients underwent open skull base surgery. Surgical approaches included transcervical (five), transfacial/maxillary swing (three), and double mandibular osteotomy (two). The vagus nerve was identified, stimulated, and monitored in all cases. Main Outcome Measures Intraoperative nerve stimulation, pre- and postoperative vagus nerve function through the use of flexible laryngoscopy in conjunction with assessment of subjective symptoms of hoarseness, voice change, and swallowing difficulty. Results Three patients had extensive involvement of the nerve by tumor with complete postoperative nerve deficit, one patient had a transient deficit following dissection of tumor off of nerve with resolution, and the remaining patients had nerve preservation. One patient experienced minor epistaxis during monitor tube placement that was managed conservatively. Conclusions Transnasal vagal nerve monitoring is a simple method that allows for intraoperative monitoring during nerve preservation surgery without limiting surgical exposure.     

Intermittent Intraoperative Neural Monitoring Technology in Minimally Invasive Video-Assisted Thyroidectomy: A Preliminary Study

Purpose: Intraoperative neural monitoring (IONM) technology was applied in minimally invasive video-assisted thyroidectomy (MIVAT) to explore its safety and effectiveness. Materials and Methods: Data were collected retrospectively from October 2009 to August 2011. Inclusion criteria included the following: (1) benign thyroid nodule with maximum diameter less than 4.0 cm by preoperative ultrasound evaluation; (2) no previous thyroid surgeries; (3) no cervical radiation history; (4) normal function of recurrent laryngeal nerve (RLN) examined by preoperative laryngoscopy; (5) patients who did not accept to take a “wait and see” follow-up strategy. Enrolled patients were randomly allocated into NIM group and control group. Results: 46 patients were enrolled in NIM group, and 51 patients were enrolled in control group. All surgeries in NIM group were performed successfully, and majority of tracheal intubations were placed with one attempt. 47 RLNs in NIM group and 60 RLNs in control group were exposed. The time of RLN locating was 6.06 ± 1.48 min in NIM group and 6.92 ± 1.34 min in control group (p = .02). The time of RLN tracing and exposing was 28.96 ± 4.75 min in NIM group and 32.17 ± 5.56 min in control group (p = .02). 1 case of temporary RLN paralysis was observed in both groups, and no permanent RLN paralysis was reported. Conclusions: The application of intermittent IONM in MIVAT is feasible. Intermittent IONM can help reduce the time of RLN locating and the time of RLN tracing and exposing.     

Intracranial Image-Guided Neurosurgery: Experience with a new Electromagnetic Navigation System

Summary. Summary. Background: The aim of image-guided neurosurgery is to accurately project computed tomography (CT) or magnetic resonance imaging (MRI) data into the operative field for defining anatomical landmarks, pathological structures and tumour margins. To achieve this end, different image-guided and computer-assisted, so-called “neuronavigation” systems have been developed in order to offer the neurosurgeon precise spatial information. Method: The present study reports on the experience gained with a prototype of the NEN-NeuroGuard^TM neuronavigation system (Nicolet Biomedical, Madison, WI, USA). It utilises a pulsed DC electromagnetic field for determining the location in space of surgical instruments to which miniaturised sensors are attached. The system was evaluated in respect to its usefulness, ease of integration into standard neurosurgical procedures, reliability and accuracy. Findings: The NEN-system was used with success in 24 intracranial procedures for lesions including both gliomas and cerebral metastases. It allowed real-time display of surgical manoeuvres on pre-operative CT or MR images without a stereotactic frame or a robotic arm. The mean registration error associated with MRI was 1.3 mm (RMS error) and 1.5 mm (RMS error) with CT-data. The average intra-operative target-localising error was 3.2 mm (± 1.5 mm SD). Thus, the equipment was of great help in planning and performing skin incisions and craniotomies as well as in reaching deep-seated lesions with a minimum of trauma. Interpretation: The NEN-NeuroGuard^TM system is a very user-friendly and reliable tool for image-guided neurosurgery. It does not have the limitations of a conventional stereotactic frame. Due to its electromagnetic technology it avoids the “line-of-sight” problem often met by optical navigation systems since its sensors remain active even when situated deep inside the skull or hidden, for example, by drapes or by the surgical microscope.     

A New Coated Bipolar Coagulator: Technical Note

Summary  Background. Sometimes charring or popping occurs and the bipolar blades get stuck to the vessel.  Methods. The tips of one of the many commercially available bipolar forceps were coated in a striped manner with Teflon −50 μ in thickness.  Results. The new bipolar coagulator coated with Teflon reduced the incidence of tissue sticking.  Conclusions. Experience with this instrument was still quite limited, but preliminary results were promising.     

Real-time integration of ultrasound into neuronavigation: technical accuracy using a light-emitting-diode-based navigation system

Summary. Background. In brain surgery, intraoperative brain deformation is the major source of postimaging inaccuracy of neuronavigation. For intraoperative imaging of brain deformation, we developed a platform for the integration of ultrasound imaging into a navigation system.Method. A commercially available ultrasound system was linked to a light-emitting-diode- (LED) based neuronavigation system via rigid fixation of a position localiser to the ultrasound probe and ultrasound image transfer into the navigation system via a S-VHS port. Since the position of the ultrasound image co-ordinate system is not readily defined within the navigation reference co-ordinate system (REF CS), a transformation which links both co-ordinate systems has to be defined by a calibration procedure. Calibration of the ultrasound probe within the REF CS was performed via a cross-wire phantom. The phantom target was defined within the navigation co-ordinate system (by pointer under microscopic control) and imaged by ultrasound. Ultrasound presets were optimised (digital beam focusing, gain intensity) to attain a small echoic target for manual target definition. The transformation was derived from 150 ultrasound measures and iteration. Accuracy was calculated as mean linear error (LE; in X_REF, Y_REF, or Z_REF direction), overall mean LE (linear errors of all axes X_REF to Z_REF) and Euclidean error (EE; vectorial distance from the physical target).Findings. Optimised ultrasound presets (8MHz frequency, digital beam focusing, 20% gain intensity) enabled a low interobserver error (mean: 0.5mm, SD: 0.28) for target definition within the 2-D ultrasound image. Mean accuracy of pointer-based physical target definition in the REF CS was 0.7mm (RMSE; SD: 0.23mm). For navigated ultrasound, the overall mean LE was 0.43mm (SD: 1.36mm; 95%CL: 3.13mm) with a mean EE of 2.26mm (SD: 0.97mm; 95%CL: 4.21mm).Interpretation. Using a single target cross-wire phantom, a highly accurate integration of ultrasound imaging into neuronavigation was achieved. The phantom accuracy of integration lies within the range of application accuracy of navigation systems and warrants clinical studies.     

The Modified Concorde Position with an Intraoperative Skew Head Rotation: Technical Note

The Concorde position was developed to approach pineal and cerebellar lesions with a midline suboccipital craniotomy. The neutral head position is needed to divide the occipital muscles symmetrically. The patient’s head is tilted to the right and the face is turned to the right for the microscopic procedure to keep the midline of the patient’s head axis straight in the surgical field for comfortable and accurate surgical manipulation. However, intraoperative repositioning of the patient’s head is somewhat difficult to release the holding arm of the Sugita head holder in the original method. We found that a skew head rotation by fixing the head asymmetrically in the Sugita head holder is very quick and convenient to obtain the optimal head position both for a craniotomy and a microscopic procedure.     

Sutureless Repair of Major Intracranial Vessels with the Sundt Clip-Graft: Technical Note

Summary Major intracranial vessels can be damaged during tumor resection. With the availability of refined microvascular techniques, direct repair or by-pass of the damaged segment is possible. These methods, however, often require temporary occlusion of the offending vessel, can result in a less than optimal angiographic result, and are difficult to perform in a deep field. Additionally, in some patients direct repair or by-pass is not feasible because of the friability of the vessel or as a result of the large size of the tear. In these cases the Sundt clip-graft represents a valid adjunct to the armamentarium of the surgeon. Over the years, it has been used by the senior author in five patients where vascular injury occurred during the removal of brain tumors (3 meningiomas, one pituitary adenoma, and one low-grade glioma). In this report we illustrate our most recent experience with this ingenious tool. A 22-year-old man underwent resection of a recurrent left temporal lobe low-grade glioma. During resection of the tumor, a tear occurred in a branch of middle cerebral artery. The tear was repaired using a Sundt clip-graft. A post-operative angiogram, performed five days later, showed patency of the vessel with no evidence of wall irregularities. Described 30 years ago to be used primarily in aneurysm surgery, the Sundt clip-graft provides an excellent, too often forgotten, sutureless method of repairing intracranial vessels damaged during tumor removal.     

Operative Record Using Intraoperative Digital Data in Neurosurgery Technical Note

Summary  Background. The purpose of this study was to develop a new method for more efficient and accurate operative records using intra-operative digital data in neurosurgery, including macroscopic procedures and microscopic procedures under an operating microscope.  Methods. Macroscopic procedures were recorded using a digital camera and microscopic procedures were also recorded using a microdigital camera attached to an operating microscope. Operative records were then recorded digitally and filed in a computer using image retouch software and database base software.  Findings. The time necessary for editing of the digital data and completing the record was less than 30 minutes. Once these operative records are digitally filed, they are easily transferred and used as database. Using digital operative records along with digital photography, neurosurgeons can document their procedures more accurately and efficiently than by the conventional method (handwriting).  Interpretation. A complete digital operative record is not only accurate but also time saving. Construction of a database, data transfer and desktop publishing can be achieved using the intra-operative data, including intra-operative photographs.     

Versatile Intraoperative MRI in Neurosurgery and Radiology

Summary. Summary.   Background: Several models for the application of intra-operative magnetic resonance imaging (IMRI) have recently been reported, most of them unique. Two fundamental issues need to be addressed: optimal use of the scanner to ensure a wide base for research, development and clinical application, and an organisational model that facilitates such use.   Method: While in our setting the IMRI project was initiated by the neurosurgeons, the need for wider use of the facilities was recognised since the beginning of the planning phase in 1996. An organisational model was developed that allowed for development of neurosurgical applications, radiological imaging, and radiological interventions and for the research and development work of the vendor. A resistive 0.23 T MR scanner was installed in a dedicated operating room environment. Unique to this scanner is the ability to turn off the magnet, allowing for normal OR activities and devices, and to turn on the magnet as needed with a relatively short six-minute ramp up time. A staged surgical technique was perfected, allowing for transfer of data to the neuronavigator outside the scanner during surgery. In neurosurgery, IMRI was used as one part of a neuronavigational system that included ultrasound imaging, intra-operative cortical stimulation during awake procedures, electrocorticography and two neuronavigators.   Findings: 34 neurosurgical cases included 27 brain tumour resections, 5 brain tumour biopsies, 1 extirpation of an arterio-venous malformation, and 1 haematoma evacuation. The scanner could also be used for normal clinical imaging where obese patients, children, claustophobic patients and postoperative control examinations were the major groups. The radiologists performed 110 interventions, including bone and abdominal biopsies, nerve root infiltrations and local pain therapies, with the optical needle tracking system under continuous MRI guidance. The organisational model allowed frequent use of the facilities for both neurosurgery and radiology and continuous development of the facilities. Intra-operative ultrasound was used in 20 tumour resections and in two open brain biopsies. This resulted in reduction of the number of MR imaging sessions during surgery. Five of the 27 resections were performed as awake craniotomies with cortical stimulation. For two of the resections, electrocorticography and depth electrode registrations were used. Furthermore, various non-MRI-compatible instruments and devices were used.   Interpretation: Intra-operative MRI is an imaging tool that can be useful especially in the context of neuronavigation. A scanner that can be turned off during surgery is particularly appropriate for neurosurgery. The concept of joint use of such facilities with other clinicians is mutually worthwhile.     

A Microsurgical Technique for Posterior Lumbar Interbody Fusion: Technical Note

Summary  Objective. To describe a microsurgical modification of the Ray Threaded Fusion Cage (TFC) instrumentation technique for achieving lumbar interbody fusion.  Technique. The lumbar fusion is established by application of two titanium cages through two different short skin incisions, first on one and then on the other side. The spinous processes and the whole interspinous ligament are preserved. Under microscopic control, the lower nerve root and foramen are identified and foraminotomy performed. The dural sac is carefully exposed so that a free and gentle retraction of the nerve root to the midline can be obtained. After removal of the disc material, the retractor is inserted. Special attention should be paid to visualization of the superior nerve root in order to avoid neural injuries. The end plate and disc material are then drilled and tapped for insertion of the appropriate cage.  Conclusion. The Ray TFC lumbar fusion can be practically and safely performed under microscopic control.     

Radiofrequency thermal ablation for recurrent meningioma extending extracranially

Summary Background. Image-guided and temperature-controlled radiofrequency thermal ablation techniques were applied to reduce tumor volume and relieve the symptoms caused by extracranial extension of recurrent meningioma.Method. We treated two patients with recurrent meningioma, an 81-year-old woman presenting with bulging of the temple and a 68-year-old woman presenting with visual disturbance, facial disfigurement, and sensory disturbance. Neuroimaging in both patients, revealed a large tumor extending extracranially and involving the infratemporal fossa. To avoid injury to important anatomical structures either compressed or entrapped by the tumor, the spatial relation between the planned ablation volume and these structures was confirmed by 3-D reconstruction of the ablation target. During the ablation procedure, local temperatures over the tissue being cauterized were continuously monitored to limit the ablation area to that within the planned volume adjusting RF power.Finding. Radiofrequency ablation produced tumor necrosis as planned without adverse effects and resulted in swift relief of symptoms and signs with shrinkage of the tumor.Conclusion. This technique may be an effective alternative for recurrent meningiomas extending extracranially and for which radical surgical procedures are not indicated.     

Impact of Intraoperative 3-Tesla MRI on Endonasal Endoscopic Pituitary Adenoma Resection and a Proposed New Scoring System for Predicting the Utility of Intraoperative MRI

The aim of this study was to evaluate the impact of 3-Tesla intraoperative high-field magnetic resonance imaging (3T-iMRI) for pituitary adenoma resection, and to propose a new scoring system for predicting the utility of 3T-iMRI. This retrospective study evaluated 82 patients with pituitary adenoma who underwent purely endoscopic endonasal resection with 3T-iMRI between 2015 and 2019. 3T-iMRI revealed unexpected residual tumor in 39 cases (47.6%), which led to further resection and contributed to upgrading of the resection level in 28 cases (34.1%), which led to gross total resection rates (GTRs) of 67.1% and near total resection of 15.9%. To construct a new scoring system, patients were divided into a discovery cohort (56 patients) and a validation cohort (26 patients). Three variables for the scoring system were selected according to a univariate analysis of the discovery cohort: the size of the tumor (>20 mm: 1 point), the presence of suprasellar tumor lobulation (1 point) and the history of previous operations (1 point). The risk of additional resection after iMRI was well stratified by this scoring system (range 0–3; p = 0.0037 for trend). Robustness of the system was confirmed in the validation cohort (0 points, 0%; 1 point, 30.8%; 2 points, 70.0%; 3 points, 100%; p = 0.0116 for trend). These results indicate that 3T-iMRI optimized the extent of resection, even with the use of an endoscope, and that the proposed scoring system is useful for predicting whether 3T-iMRI is likely to be of value for a particular patient.     

Transzygomatic Approach with Intraoperative Neuromonitoring for Resection of Middle Cranial Fossa Tumors

The authors reviewed the surgical experience and operative technique in a series of 11 patients with middle fossa tumors who underwent surgery using the transzygomatic approach and intraoperative neuromonitoring (IOM) at a single institution. This approach was applied to trigeminal schwannomas (n = 3), cavernous angiomas (n = 3), sphenoid wing meningiomas (n = 3), a petroclival meningioma (n = 1), and a hemangiopericytoma (n = 1). An osteotomy of the zygoma, a low-positioned frontotemporal craniotomy, removal of the remaining squamous temporal bone, and extradural drilling of the sphenoid wing made a flat trajectory to the skull base. Total resection was achieved in 9 of 11 patients. Significant motor pathway damage can be avoided using a change in motor-evoked potentials as an early warning sign. Four patients experienced cranial nerve palsies postoperatively, even though free-running electromyography of cranial nerves showed normal responses during the surgical procedure. A simple transzygomatic approach provides a wide surgical corridor for accessing the cavernous sinus, petrous apex, and subtemporal regions. Knowledge of the middle fossa structures is essential for anatomic orientation and avoiding injuries to neurovascular structures, although a neuronavigation system and IOM helps orient neurosurgeons.     

Real Time Parallel Intraoperative Integration of Endoscopic,Microscopic, and Navigation Images: A Proof of Concept Based on Laboratory Dissections

Endoscope, microscope, and neuronavigation systems are integrated in neurosurgical procedures mainly by using a serial combination algorithm, where, the user must switch his/her field of view from one platform display to another. The integration of theses devices could be optimized by incorporating different displays into one viewing platform thus achieving a parallel combination. In this study, we investigated the feasibility and the applicability of parallel integration of microscopic, endoscopic, and neuronavigation images by real time displaying the endoscope and neuronavigation image datasets in the main operative microscope oculars. The proposed set-up was effective in displaying the three images dataset in an operationally actionable mode. Ergonomically, the ability of using the different image dataset without the need of taking the eyes off the microscope oculars did not disrupt the flow or the tempo of the operative procedure. However, new endoscopes specific to this application are recommended.     

Identification of Somatosensory Pathways by Focal-Cooling-Induced Changes of Somatosensory Evoked Potentials and EEG-Activity – an Experimental Study

Summary  Object. Function-preserving neurosurgery requires methods to identify functionally important CNS-areas intraoperatively. We investigated whether a combination of focal cerebro-cortical cooling and monitoring of somatosensory evoked potentials (SEP) is suited for this task, i.e. whether it is able to outline structures belonging to the somatosensory pathway.  Methods. In 17 Wistar rats the somatosensory cortex was focally cooled by 20°C below the initial tissue temperature for periods of five minutes. A cryoprobe with a tip diameter of 3 mm was used and tissue temperatures were measured below and at different distances to the cryoprobe. Tibial nerve evoked SEPs and EEG-spectra were recorded continuously.  Results. During cortical cooling the SEP-responses showed a marked delay and amplitude increase of the cortically generated components P13 and N18 and a small latency increase of the subcortically generated wave III. EEG-spectra were depressed mainly in the low frequency range. All cooling effects were reversible and in light- as well as electron-microscopic examinations no tissue damage was found.  Conclusions. Focal cooling of the cortex induces easily recognizable and reversible changes of the bio-electrical activity without causing any histological damage. Therefore the method seems suitable for identifying eloquent areas. It can be expected that clinical application of the cooling technique in combination with intraoperative electrophysiological monitoring will be helpful to further lower the risk of neurosurgical operations.  We propose that cooling mainly interferes with the synaptic transmission within the somatosensory cortex, because the observed amplitude increase can be explained by cold-induced depression of inhibitory cortical activity (disinhibition).     

Transsphenoidal-Transtuberculum Sellae Approach for Supradiaphragmatic Tumours: Technical Note

Summary  The Classic transsphenoidal approach may not afford sufficient exposure for a supradiaphragmatic tumour adjacent to the pituitary stalk. Various transcranial approaches have been utilized to access such a lesion with adequate results. This report describes a less invasive technique, termed “transsphenoidal-transtuberculum sellae approach”. This modified transsphenoidal approach requires a bone ablation of the tuberculum sellae, the limbus sphenoidalis, and a portion of the planum sphenoidale, in addition to an opening of the anterior floor of the sella turcica. The dura mater on the tuberculum sellae and the pituitary fossa is sectioned with a bilateral obliteration of the anterior intercavernous sinus. The anterior pituitary gland is not necessarily resected. The optic chiasm, optic nerves, pituitary stalk, and tuber cinereum can be directly observed, making it possible to safely dissect a lesion from these structures. Utilizing this approach, we have removed 14 supradiaphragmatic tumours without complications and dealt with other lesions such as optic nerve injuries or cerebrospinal fluid rhinorrhea, leaving pituitary function intact. The transsphenoidal-transtuberculum sellae approach for accessing small supradiaphragmatic tumours is a useful procedure requiring only a minor modification of the classic transsphenoidal technique.