Intraoperative Neuromonitoring Results Research Articles

Is the Use of Intraoperative Neuromonitoring Justified During Lumbar Anterior Approach Surgery?

Intraoperative neuromonitoring (IONM) became widely used in spine surgery to reduce the risk of iatrogenic nerve injury. However, the proliferation of IONM has fallen into question based on effectiveness and costs, with a lack of evidence supporting its benefit for specific spine surgery procedures. The purpose of this study was to evaluate the use of IONM and the rate of neurological injury associated with anterior lumbar spinal surgery. This was a retrospective study on a consecutive series of 359 patients undergoing lumbar anterior approach surgery for anterior lumbar interbody fusion (ALIF), total disc replacement (TDR), or hybrid (ALIF with TDR) for the treatment of symptomatic disc degeneration. Patients undergoing any posterior spine surgery were excluded. Operative notes were reviewed to identify any changes in IONM and the surgeon's response. Clinic notes were reviewed up to 3 months postoperatively for indications of iatrogenic nerve injury. There were 3 aberrant results with respect to IONM. Changes in IONM of a lower extremity occurred for 1 patient (0.3%). The surgeon evaluated the situation and there was no observable reason for the IONM change. Upon waking, the patient was found to have no neurological deficit. There were 2 cases of neurologic deficits in this population, which were classified as false-negatives of IONM (0.56%, 95% CI: 0.1% to 1.8%). In both cases, the patients were found to have a foot drop after the anterior approach surgery. In this study, there was 1 false-positive and 2 false-negative results of IONM. These data suggest that IONM is not beneficial in this population. However, many surgeons may feel obligated to use IONM for medicolegal reasons. There is a need for future studies to delineate cases in which IONM is beneficial and the type of monitoring to use, if any, for specific spine surgery types. This study questions the routine use of IONM in anterior lumbar approach surgery for the treatment of symptomatic disc degeneration. This has significant implications related to the cost of this practice.

The advantage of the combined use of intraoperative neuromonitoring and percutaneous ultrasonography of the larynx as a screening for postoperative vocal cord paresis

Background. One of the most common complications during thyroid surgery after hypoparathyroidism is a violation of the mobility of the vocal folds - paresis or paralysis of the larynx. The incidence of damage to the recurrent laryngeal nerves during primary surgical interventions can vary from 1 to 30%. Intraoperative neuromonitoring is the most effective method to reduce the amount of damage to the laryngeal nerves during surgical interventions on the thyroid and parathyroid glands. Assessment of the state of the vocal cords in the preoperative and postoperative period is crucial. In the preoperative period, this helps establish baseline characteristics and identify pre-existing laryngeal paresis, while postoperative early identification of vocal cord paresis helps develop a rapid treatment plan. Indirect laryngoscopy is still considered the reference standard for vocal cord examination. The main advantage is the ability to visualize the vocal cords in 99% of cases. However, this is an invasive procedure that can be painful and uncomfortable for patients, and increases medical costs and lead time.Materials and methods. The results of intraoperative neuromonitoring were analyzed in 25 patients who underwent total thyroidectomy according to indications (diffuse nodular non-toxic goiter — 17 patients (68%), diffuse nodular toxic goiter — 4 patients (16%), autoimmune thyroiditis, diffuse — nodular form — 4 patients (16%)), from September 2021 to February 2022. The patients’ age ranged from 18 to 73 years. There were 23 women (92%), men — 2 (8%). In the study, a C2 neuromonitor (InoMed, Germany), an electrode for EMG recording on an endotracheal tube, and a bipolar forked stimulating probe were used. To assess the mobility of the vocal folds, all patients underwent percutaneous ultrasonography before and after thyroid surgery.Results and discussion. In 20 patients (80%) before surgery on transcutaneous ultrasound of the larynx, the visualization of the structures of the larynx was good (grade 4-5), in 2 male patients (8%), the visualization of the structures of the larynx was satisfactory (grade 3), in 3 women (older than 45 years (12%)) — visualization of the structures of the larynx was satisfactory (grade 3), in all 25 patients (100%) — complete or normal symmetrical movement of the vocal folds (grade I). During the performance of precision extrafascial thyroidectomy in 3 patients (12%), a decrease in the amplitude of oscillations was recorded during stimulation of the left recurrent laryngeal nerve and the left vagus nerve, in order to prevent bilateral paresis of the larynx, it was decided to confine ourselves to hemithyroidectomy followed by a staged right-sided hemithyroidectomy. A day after the performed left-sided hemithyroidectomy, percutaneous ultrasound of the larynx in 2 patients showed a violation of the mobility of the vocal fold on the left (grade II), in 1 patient — symmetrical movement of the vocal folds (grade I) — a false positive reaction. In 22 patients (88%) who underwent total thyroidectomy on percutaneous ultrasound of the larynx, complete or normal symmetrical movement of the vocal folds (I degree).Conclusion. Intraoperative neuromonitoring is an effective tool to localize the recurrent laryngeal nerves regardless of whether a loss of signal (LOS) has occurred, as well as to determine the type of LOS (LOS 1, LOS 2) and staged thyroidectomy in the presence of LOS. Percutaneous vocal cord ultrasonography is currently an effective screening tool, saving 80% of patients from unnecessary invasive laryngoscopy. The complex of these methods should be an obligatory component in surgical interventions on the thyroid and parathyroid glands.

Intraoperative MRI-based elastic fusion for anatomically accurate tractography of the corticospinal tract: correlation with intraoperative neuromonitoring and clinical status.

Tractography is a useful technique that is standardly applied to visualize subcortical pathways. However, brain shift hampers tractography use during the course of surgery. While intraoperative MRI (ioMRI) has been shown to be beneficial for use in oncology, intraoperative tractography can rarely be performed due to scanner, protocol, or head clamp limitations. Elastic fusion (EF), however, enables adjustment for brain shift of preoperative imaging and even tractography based on intraoperative images. The authors tested the hypothesis that adjustment of tractography by ioMRI-based EF (IBEF) correlates with the results of intraoperative neuromonitoring (IONM) and clinical outcome and is therefore a reliable method. In 304 consecutive patients treated between June 2018 and March 2020, 8 patients, who made up the basic study cohort, showed an intraoperative loss of motor evoked potentials (MEPs) during motor-eloquent glioma resection for a subcortical lesion within the corticospinal tract (CST) as shown by ioMRI. The authors preoperatively visualized the CST using tractography. Also, IBEFs of pre- and intraoperative images were obtained and the location of the CST was compared in relation to a subcortical lesion. In 11 patients (8 patients with intraoperative loss of MEPs, one of whom also showed loss of MEPs on IBEF evaluation, plus 3 additional patients with loss of MEPs on IBEF evaluation), the authors examined the location of the CST by direct subcortical stimulation (DSCS). The authors defined the IONM results and the functional outcome data as ground truth for analysis. The maximum mean ± SD correction was 8.8 ± 2.9 (range 3.8-12.0) mm for the whole brain and 5.3 ± 2.4 (range 1.2-8.7) mm for the CST. The CST was located within the lesion before IBEF in 3 cases and after IBEF in all cases (p = 0.0256). All patients with intraoperative loss of MEPs suffered from surgery-related permanent motor deficits. By approximation, the location of the CST after IBEF could be verified by DSCS in 4 cases. The present study shows that tractography after IBEF accurately correlates with IONM and patient outcomes and thus demonstrates reliability in this initial study.

Filum terminale lipomas-the role of intraoperative neuromonitoring.

Filum terminale lipomas (FTL) represent a sub-type of spinal lipomas, where there is fatty infiltration of the filum. It becomes a surgical entity when it manifests as clinical or radiological tethered cord syndrome. Intraoperative neuromonitoring (IONM) has been suggested as a valuable tool in children for tethered cord surgeries. FTL is distinct and cannot be compared with complex tethered cord syndrome (TCS). Untethering an FTL is a relatively straightforward microsurgical exercise, usually based on anatomical findings. Neurological morbidity in FTL untethering is extremely low. The necessity of IONM in FTL has not been evaluated. The objective of this study was to identify the role of IONM in untethering an FTL METHODS: Available electronic data and case files were interrogated to identify children (0-18 years) who underwent an untethering of FTL between 2008 and 2019. We had a shift in our policy and tried to use IONM as often as possible in all tethered cord surgery from 2014. All children were categorised under 'IONM implemented' or 'no IONM' group. Outcomes analysed were as follows: (1) Clinical status on short-term and long-term follow-up, (2) alteration of surgical course by IONM and (3) complications specifically associated with IONM RESULTS: Among 80 children included in this study, IONM was implemented in 37 children and 43 children underwent untethering without IONM. 32.5% of children were 'syndromic'. Seventy-five percent of children were under age 3 years during surgery. Both groups (No IONM vs. IONM implemented) were well matched in most variables. Majority of 'no IONM' surgeries were performed prior to 2014. There was no neurological morbidity in the entire cohort. Mean duration of follow-up was 49.10 (± 33.67) months. Short-term and long-term clinical status remained stable in both cohorts. In 16 children, the filum was stimulated. Based on our protocol, majority had a negative response. One child showed a positive response, contradicted by thorough microscopic inspection. Despite a positive response, the filum was untethered. IONM was not associated with any complication in this study. FTL untethering is an inherently low-risk microsurgery in experienced hands with rarely reported neurological morbidity. IONM may not be required for all FTL and may be used more judiciously.

The Utility of Preoperative Neuromonitoring for Adolescent Idiopathic Scoliosis.

Intraoperative neuromonitoring is well established and widely used to assist in completing corrective surgery for adolescent idiopathic scoliosis (AIS) safely. The role of preoperative measurement of somatosensory evoked potentials (SSEPs) and/or transcranial magnetic stimulation (TMS) to determine if there is transpinal pathology, however, is not clear. We sought to determine if preoperative SSEP and/or TMS measurement provided clinical benefit to patients with AIS. A review of medical charts between 2010 and 2012 was conducted for patients undergoing surgery for scoliosis. Patients with diagnoses other than AIS were excluded. Patients with incomplete preoperative or intraoperative data were also excluded. Relevant clinical information such as age, sex, number of levels fused, and major Cobb angle were recorded. Preoperative neuromonitoring measurements and intraoperative neuromonitoring results were reviewed by an attending neurologist. Any instance in which an intraoperative surgical plan or neuromonitoring result interpretation was influenced by preoperative results was recorded. Further imaging obtained based on preoperative results was noted. Any acute neurologic complication such as paralysis was noted. Eighty-one patients met inclusion criteria (64 female, 17 male). Average age was 15 years (± 1.92). Major Cobb angle at preoperative evaluation averaged 57.5 degrees (± 10.81 degrees). Ten patients had abnormal preoperative SSEP/TMS results. There were no changes in protocol during intraoperative neuromonitoring based upon preoperative neuromonitoring findings. No additional imaging was required for patients with abnormal preoperative neuromonitoring results. There was no statistically significant difference in preoperative Cobb angle between the group of patients with abnormal preoperative neuromonitoring and those with normal baseline testing. Preoperative SSEP/TMS measurement prior to corrective surgery for AIS has limited utility. There were no instances in which a patient's clinical course was improved by testing. We recommend against routine use of preoperative SSEP/TMS testing for AIS patients requiring corrective surgery.

Anesthetic Considerations of Intraoperative Neuromonitoring in Thyroidectomy.

Intraoperative neuromonitoring (IONM) might reduce the incidence of injury to the recurrent laryngeal nerve (RLN) during thyroidectomy. Although dislocation of endotracheal tube surface electrodes can lead to false-positive IONM results (loss of signal), the risk factors for dislocation and the effects of muscle relaxants are unclear. Therefore, to identify factors that affect IONM results, we examined the frequency and risk factors for tube dislocation after cervical extension before surgery, the effect of sugammadex administration, and the correlation between IONM results and postoperative RLN palsy. Thirty-nine patients scheduled for thyroidectomy from October 2016 to April 2017 were enrolled. All patients underwent standard IONM and pre- and postoperative laryngoscopy. Differences in patient characteristics in the tube dislocation group and non-dislocation group, and differences in amplitude during vagal stimulation before and after sugammadex administration, were assessed by the Mann-Whitney test or Fisher's exact test. Tube dislocation occurred in 27 patients (69%). Sterno-cricoid distance was significantly shorter in the dislocation group (n=27) than in the non-dislocation group (n=12) (43.88 [32.2-55.91] mm vs 49.46 [40.66-55.91] mm, respectively; p=0.048). Without sugammadex, amplitude during vagal stimulation was sufficient for monitoring. Nine patients had new-onset RLN palsy, which was transient in all patients. The sensitivity of IONM was 100%, the positive predictive value was 60%, and the negative predictive value was 100%. The present findings suggest that anesthesiologists should use video laryngoscopy to correct tube dislocation and that a rocuronium dose of 0.6 mg/kg, without sugammadex, is adequate for IONM.

Rating of intra-operative neuro-monitoring results in operative correction of the spinal deformities

Purpose of the work was filing the electrophysiological phenomena observed in the process of intra-operative neuromonitoring followed by development of the results’ scale of intra-operative neuro-physiological testing of the pyramidal tract. Materials and мethods. The selection for evaluation included data of 147 protocols of intra-operative neuromonitoring in 135 patients (53 males, 82 females), aged from 1 y. 5 m. to 52 years (14,1±0,7 years) with spinal deformities of different etiology who underwent instrumentation spinal correction followed by fixation of thoracic / thoracolumbar spine segments using various variants of internal systems of trans-pedicular fixation. Intra-operative neuro-monitoring was performed using system «ISIS IOM» (Inomed Medizintechnik GmbH, Germany). The changes of motor evoked potentials were evaluated according to this scale. Results. Five types of pyramidal system reaction to operative invasion were revealed. According to neurophysiological criteria three grades of the risk of neurological disorders development during operative spinal deformity correction and, correspondingly, three levels of anxiety for the surgeon were defined. Conclusion. Intra-operative neurophysiological monitoring is the effective highly technological instrument to prevent neurological disorders in the spinal deformity. Offered rating scale of the risk of neurological complications gives the possibility to highlight three levels of anxiety during operative invasion.

Double probe intraoperative neuromonitoring with a standardized method in thyroid surgery

IntroductionThe purpose of this study was to evaluate the effectiveness of intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN) and the vagus nerve (VN) with a standardized approach in thyroid surgery. MethodsRetrospective study with an experimental group with which IONM was used, both with the RLN that the VN, and a control one, each consisting of 300 total thyroidectomies. Each patient underwent a pre-and post-operative videolaryngoscopy. The number of RLNs identified and the number of transient and permanent RNL injuries for each group were assessed, and then compared with χ2 tests. In the experimental group Sensitivity, Specificity, Positive Predictability, Negative Predictability and Accuracy of IONM were evaluated, depending on the number of true positive results, false negatives, true negatives and false positives obtained by comparing the results of IONM with the post-operative videolaryngoscopies. ResultsThe results obtained for the experimental group vs. the control group were: RLNs identified 595 (99.1%) vs. 552 (92%) -P Value <0.0001; Permanent RLNs injuries 4 (1.33%) vs. 5 (1.67%) -P Value 1; transient RLNs injuries 1 (0.33%) vs. 8 (2.67%) -P Value 0.044.The IONM system, for the RLN and VN showed respectively: Sensitivity 66.7% vs. 83.3%; specificity 97.6% vs. 99.5%; Positive Predictability 22.2% vs. 62.5%; Negative Predictability 99.6% vs. 99.3%; Accuracy 97.3% vs. 99.3%. ConclusionsOur study highlights that using IONM with a standardized method in thyroid surgery, improves the ability to identify the RLN and a reduction in the incidence rate of transient RLN injuries.

Surgical strategy during intended total thyroidectomy after loss of EMG signal on the first side of resection

Unambiguous identification of the recurrent laryngeal nerve with detection of nerve dysfunction giving rise to postoperative vocal cord palsy (VCP) is the principal objective of intraoperative neuromonitoring (IONM) in thyroid surgery. Because intraoperative loss of the electromyographic (EMG) signal (LOS) does not result in VCP in one third of patients, controversy surrounds the issue of whether a change in strategy is needed in planned total thyroidectomy after LOS on the first side of resection. This was a retrospective institutional study of 1,049 consecutive patients (2,086 nerves at risk) with intended bilateral thyroid surgery who were operated on between April 2010 and July 2012 with the use of IONM. The rates of temporary and permanent VCP were analyzed on the basis of the IONM results of the first side of resection and the extent of contralateral resection for completion: resection without LOS (group1); resection with LOS and contralateral thyroidectomy (group2); resection with LOS and contralateral subtotal resection (group3); resection with LOS without any contralateral resection (group4). LOS on the first side of resection was noted in 27 patients (2.6 %). All VCPs were unilateral. The rates of temporary and permanent VCP were 2.5 and 0.4 %, respectively, overall; specifically: group1: 0.5 and 0 %; group2: 64 and 9.1 %; group3: 100 and 50 %; group4: 83 and 8.3 %, respectively. Because an abnormal intraoperative electromyogram carries an 80 % risk for early postoperative VCP, the initial plan of bilateral surgery needs to be critically reviewed after LOS has occurred on the first side of resection, taking into account the underlying thyroid disease of the patient and surgeon expertise. Since more than 80 % of affected nerves will fully recover after the operation, staged completion thyroidectomy is recommended.

Results of Intraoperative Neuromonitoring in Thyroid Surgery and Preoperative Vocal Cord Paralysis

Systematic studies of intermittent intraoperative neuromonitoring (IONM) have shown that IONM enhances recurrent laryngeal nerve (RLN) identification via functional assessment, but does not significantly reduce rates of vocal cord (VC) paralysis (VCP). The reliability of functional nerve assessment depends on the preoperative integrity of VC mobility. The present study was therefore performed to analyze the validity of IONM in patients with pre-existing VC paralysis. Of 8,128 patients, 285 (3.5%) with preoperative VCP underwent thyroid surgery using standardized IONM of the RLN and vagus nerves (VNs). VC function was assessed by pre- and postoperative direct videolaryngoscopy. Quantitative parameters of IONM in patients with VCP were compared with IONM in patients with intact VC function. Clinical symptoms and surgical outcomes of patients with pre-existing VCP were analyzed. A total of 244 patients revealed negative, and 41 revealed positive IONM on the side of the VCP. VCP with positive IONM revealed significantly lower amplitudes of VN and RLN than intact VN (p=0.010) and RLN (p=0.011). Symptoms of patients with VCP included hoarseness (25%), dyspnea (29%), stridor (13%), and dysphagia (13%); 13% were asymptomatic. New VCP occurred in five patients, ten needed tracheostomy for various reasons, and one patient died. Patients with pre-existing VCP revealed significantly reduced amplitude of ipsilateral VN and RLN, indicating retained nerve conductivity despite VC immobility. Preoperative laryngoscopy is therefore indispensable for reliable IONM and risk assessment, even in patients without voice abnormalities.

Total Mesorectal Excision with Intraoperative Assessment of Internal Anal Sphincter Innervation Provides New Insights into Neurogenic Incontinence

The aim of this prospective study was to assess internal anal sphincter (IAS) innervation in patients undergoing total mesorectal excision (TME) by intraoperative neuromonitoring (IONM). Fourteen patients underwent TME. IONM was carried out through pelvic splanchnic nerve stimulation under continuous electromyography of the IAS. Anorectal function was assessed with the digital rectal examination scoring system and a standardized questionnaire. Nine of 11 patients who underwent low anterior resection had positive IONM results, with stimulation-induced increased IAS electromyographic amplitudes (median 0.23 μV (interquartile range [IQR] 0.05, 0.56) vs median 0.89 μV (IQR 0.64, 1.88), p < 0.001) after TME. The patients with the positive IONM results were continent after stoma closure. Of 2 patients with negative IONM results, 1 had fecal incontinence after closure of the defunctioning stoma and received a permanent sigmoidostomy. In the other patient the defunctioning stoma was deemed permanent due to decreased anal sphincter function. In 3 patients who underwent abdominoperineal excision, IONM assessed denervation of the IAS after performance of the abdominal part. This study demonstrated that IONM of IAS innervation in rectal cancer patients is feasible and may predict neurogenic fecal incontinence.

The Impact of Intraoperative Neuromonitoring (IONM) on Surgical Strategy in Bilateral Thyroid Diseases: Is it Worth the Effort?

Intraoperative nerve monitoring (IONM) of the recurrent laryngeal nerve and the vagal nerve can detect nonfunctioning nerves (recurrent laryngeal nerve palsy, RLNP) that are visibly intact. The use of IONM is questionable, however, as we still lack evidence that it reduces the rate of postoperative nerve injuries. Since negative IONM results after thyroid dissection of the first side could change our surgical strategy and thus could prevent patients from bilateral RLNP, we questioned whether IONM results are reliable enough to base changes in surgical strategy and whether this has any effect on surgical outcome. We retrospectively analyzed the data of 1333 consecutive patients with suggested benign bilateral thyroid disease who had been operated on under a defined protocol, including the use of a specific IONM technique (tube electrodes and stimulation of the vagal nerve and the inferior recurrent nerve before and after thyroid resection), between January 1, 2006 and December 31, 2008. In four patients the IONM system did not work, two nerves had not been found, and in eight patients the tube had to be readjusted. Of five permanent nerve injuries, four were visible during surgery and one was suspected. Sensitivity of IONM in detecting temporary nerve injuries of macroscopically normal-appearing nerves was 93%. Specificity was 75-83% at first side of dissection and 55-67% at the second side, with an overall specificity of 77%. In 11 of 13 patients (85%) with known nerve injury (preexisting or visible) and in 20 of 36 patients (56%) with negative IONM stimulation at the first side of dissection, the surgical strategy was changed (specific surgeon or restricted resection) with no postoperative bilateral RLNP. This was in contrast to 3 of 18 (17%) bilateral RLNP (p < 0.05), when surgeons were not aware of a preexisting or highly likely nerve injury at the first side of thyroid dissection. Failed IONM stimulation of the vagal or recurrent laryngeal nerve after resection of the first thyroid lobe is specific enough to reconsider the surgical strategy in patients with bilateral thyroid disease to surely prevent bilateral RLNP.

Standardization of Intraoperative Neuromonitoring of Recurrent Laryngeal Nerve in Thyroid Operation

The lack of standardized procedures of intraoperative neuromonitoring (IONM) during thyroid operations may lead to highly variable results, and many of these results can cause misleading information and, conversely, increase the risk of recurrent laryngeal nerve (RLN) injury. Therefore, standardization of IONM procedures is necessary. A total of 289 patients (435 nerves at risk) who underwent thyroidectomy by the same surgeon were enrolled in this study. Each patient was intubated with EMG endotracheal tube by the same anesthesiologist. Standardized IONM procedures were applied in each patient. The procedures include preoperative and postoperative video-recording of vocal cord movement, ensuring the correct position of electrodes after the neck was placed at full extension, vagal stimulation and registration of EMG signals before and after RLN dissection, and photographic documentation of the exposed RLN. Five patients encountered dysfunction of IONM, which was caused by malposition of electrodes and the problem was detected at once. One patient with non-RLN was detected at the earlier stage of operation. Eighteen nerves experienced loss of EMG signals during thyroid dissection, and the causes of nerve injuries were well elucidated with the application of our standardized IONM procedures. The standardized IONM procedures are useful and helpful not only to eliminate false IONM results, but also to elucidate the mechanism of RLN injury. After ascertaining the surgical pitfalls and improving the surgical techniques, the palsy rate was significantly reduced in this study.

Surgical resection of gliomas WHO grade II and III located in the opercular region.

Surgery in the opercular region especially in the dominant hemisphere impose a major challenge for the neurosurgeon due to the close vicinity to functional important motor and speech areas. The purpose of the present study is to analyse on a homogenous patient group pre- and postoperative functional deficits with regard to different speech qualities (e.g. aphasia, apraxia), and to correlate these data with MR and intraoperative monitoring results. Fourteen patients with suspected low grade astrocytomas in the opercular region consecutively treated by surgery were eligible for this study (histology revealed 3 WHO grade III tumours). Degree and duration of postoperative deficits were retrospectively evaluated according to tumour location and boundaries on MR, intraoperative neuromonitoring results and extent of tumour resection. Postoperatively, 8 patients showed speech or language disturbances, in 4 patients combined with motor deficits mainly of the contralateral upper extremity. Fifty percent of the neuropsychologically tested patients exhibited speech apraxia while the other 50% had a true aphasic syndrome. Recovery of the latter deficits was in general faster and more complete. The severity and duration of postoperative deficits was in good correlation with the distance of the resection margin to the next positive stimulation point(s), and a distance of more than 0.5 cm proved to avoid major impairments. The distribution of functional important stimulation points in relation to the tumour extension was not predictable, and -- unexpectedly -- up to 50% of these sites were found overlaying the tumour. Surgery for WHO grade II and III gliomas in the opercular region can result in speech apraxia or an aphasic syndrome with or without concomitant motor deficits. Intraoperative cortical electrical stimulation is essential in resecting tumours in the opercular region to avoid permanent morbidity.

Surgical resection of grade II astrocytomas in the superior frontal gyrus.

Surgery in the superior frontal gyrus partially involving the supplementary motor area (SMA) may be followed by contralateral transient weakness and aphasia initially indistinguishable from damage to the primary motor cortex. However, recovery is different, and SMA deficits may resolve completely within days to weeks. No study has assessed the distinct postoperative deficits after tumor resection in the SMA on a homogeneous patient group. Twenty-four patients with World Health Organization Grade II astrocytomas in the superior frontal gyrus consecutively treated by surgery were studied. Degree and duration of postoperative deficits were evaluated according to tumor location and boundaries via magnetic resonance imaging scans, intraoperative neuromonitoring results, and extent of tumor resection. Postoperatively, motor deficits were evident in 21 of 24 and speech deficits in 9 of 12 patients. Motor function quickly recovered in 11 and speech function in 3 patients. None of the 12 patients in whom the posterior tumor resection line was at a distance of more than 0.5 cm from the precentral sulcus experienced persistent motor deficits. Eight of these patients developed typical SMA syndrome with transient initiation difficulties. Seven of 12 patients in whom the tumor extended to the precentral sulcus still had motor deficits at the 12-month follow-up assessment. Surgery for Grade II gliomas in the superior frontal gyrus is more likely to result in permanent morbidity when the resection is performed at a distance of less than 0.5 cm from the precentral gyrus or positive stimulation points. Therefore, cortical mapping of motor and speech function, in critical cases under local anesthesia with the patient as his or her own monitor, is recommended; resection should be tailored to obtain good functional outcome and maintain quality of life.