Georg Neuloh

Motor Evoked Potential Monitoring with Supratentorial Surgery

OBJECTIVE To assess feasibility and clinical value of motor evoked potential (MEP) monitoring with surgery close to supratentorial motor areas and pathways. METHODS Functional mapping by somatosensory evoked potential phase reversal and continuous MEP recording after high-frequency repetitive electrical cortex stimulation was performed during 182 operations in 177 patients. Significant MEP changes were reported to trigger surgical reaction. Intraoperative surgical and electrophysiological findings were documented prospectively. Patient files were reviewed for clinical data. MEP monitoring results were correlated with motor outcome. RESULTS MEP recording was successful in 167 cases (91.8%). Inadequate electrode placement was an important reason for failed recording in the remaining patients, whereas preoperative paresis and anesthesia had no significant effect. Permanently disabling new motor deficit occurred in 8 cases (4.9%), whereas transient and nondisabling weakness was frequent (27.4%). Significant MEP changes occurred during 64 operations (39%). Irreversible MEP loss always predicted new, usually permanent, paresis. Unaltered MEP recordings indicated unimpaired motor function in the monitored muscle groups, except for rare transient deficit because of late edema and rebleeding. Irreversible MEP deterioration without loss and reversible changes could be associated with new paresis, which was transient in most patients. No major complications were observed, except for intraoperative generalized seizure in one epilepsy patient under insufficient anticonvulsant therapy. CONCLUSION MEP monitoring with supratentorial surgery is feasible and safe. It may help to maximize resection within the limits of preserved motor function. Further evidence is needed to confirm these results.

Intraoperative electrical stimulation in awake craniotomy: methodological aspects of current practice.

There is increasing evidence that the extent of tumor removal in low-grade glioma surgery is related to patient survival time. Thus, the goal of resecting the largest amount of tumor possible without leading to permanent neurological sequelae is a challenge for the neurosurgeon. Electrical stimulation of the brain to detect cortical and axonal areas involved in motor, language, and cognitive function and located within the tumor or along its boundaries has become an essential tool in combination with awake craniotomy. Based on a literature review, discussions within the European Low-Grade Glioma Group, and illustrative clinical experience, the authors of this paper provide an overview for neurosurgeons, neurophysiologists, linguists, and anesthesiologists as well as those new to the field about the stimulation techniques currently being used for mapping sensorimotor, language, and cognitive function in awake surgery for low-grade glioma. The paper is intended to help the understanding of these techniques and facilitate a comparison of results between users.

Insular gliomas: the case for surgical management

OBJECT Treatment for insular (paralimbic) gliomas is controversial. In this report the authors summarize their experience with microsurgical resection of insular tumors. METHODS The authors analyzed complications, functional outcomes, and survival in a series of 101 operations performed in 94 patients between 1995 and 2005. RESULTS A > 90% resection was achieved in 42%, and 70-90% tumor removal was accomplished in 51% of cases. Functional outcomes varied considerably between patient subgroups. For example, in neurologically intact patients < or = 40 years of age with WHO Grade I-III tumors, good outcomes (Karnofsky Performance Scale Score 80-100) were seen in 91% of cases. Predictors of an unfavorable functional outcome included histological features of glioblastoma, advanced age, and a low preoperative Karnofsky Performance Scale score. One year after surgery, 76% of patients who had presented with epilepsy were seizure free or experienced only isolated, nondebilitating seizures. Surprisingly good survival rates were seen after surgery for anaplastic gliomas. The median survival for patients with anaplastic astrocytomas (WHO Grade III) was 5 years, and the 5-year survival rate for those with anaplastic oligodendroglial tumors was 80%. Independent predictors of survival included younger age, favorable histological features (WHO Grade I and oligodendroglial tumors), Yaşargil Type 5A/B tumors with frontal extensions, and more extensive resections. CONCLUSIONS Insular tumor surgery carries substantial complication rates. However, surprisingly similar figures have been reported in large unselected craniotomy series and also after alternative treatment regimens. In view of the oncological benefits of resective surgery, our data would therefore argue for microsurgery as the primary treatment for most patients with a presumed WHO Grade I-III tumor. Patients with glioblastomas and/or age > 60 years require a more cautious approach.

Incidence, clinical manifestations, and course of water and electrolyte metabolism disturbances following transsphenoidal pituitary adenoma surgery: a prospective observational study.

OBJECT The authors prospectively studied the incidence, spectrum of clinical manifestations, course, and risk factors of water and electrolyte disturbances (WEDs) following transsphenoidal pituitary adenoma surgery. METHODS From the preoperative day to the 14th postoperative day, 57 successive patients undergoing transsphenoidal adenomectomy were monitored daily for body weight, balance of fluids, serum electrolytes, plasma osmolality, plasma antidiuretic hormone (ADH) levels, urinary sodium excretion, urinary osmolality, and subjective sensation of thirst. The type of adenoma operated on and the intraoperative manipulation of the neurohypophysis were also recorded. RESULTS Fifty-seven patients (mean age 55 years, 61.4% females) harbored 30 clinically hormone-inactive and 27 hormone-secreting pituitary adenomas. Postoperative WED occurred in 75.4% of the patients: in 38.5% as isolated diabetes insipidus (DI); in 21% as isolated hyponatremia; and in 15.7% as combined DI-hyponatremia. The maximum of medians of diuresis (5.750 L) in patients with isolated DI occurred on postoperative Day 2. Nadir of medians of hyponatremia (132 mmol/L) in patients with isolated hyponatremia occurred on postoperative Day 9. In patients with combined DI-hyponatremia, maximum of medians of diuresis (5.775 L) occurred on the 2nd day and nadir of medians of hyponatremia (130 mmol/L) on the 10th postoperative day. Altogether, 8.7% of the patients had to be treated with desmopressin because of DI persisting for >3 months. Of all the patients with hyponatremia, 42.8% were treated by transient fluid-intake restriction due to an IH of <130 mmol/L with or without clinical symptomatology. Transient acute renal failure occurred in one of these patients. Generally, the occurrence of postoperative WEDs was linked to the intraoperative manipulation of the neurohypophysis. Increased thirst correlated significantly with DI (p=0.001 and 0.02, respectively) and decreased thirst with the hyponatremic episode in patients with combined DI-hyponatremia (p=0.003). Decreased urine osmolality correlated significantly with the presence of DI (p=0.023). Electrolyte-free water clearance and urinary Na+ excretion were not correlated with DI and hyponatremia. Antidiuretic hormone was not suppressed during hyponatremia. CONCLUSIONS Water and electrolyte disturbances occurred in the majority of patients undergoing transsphenoidal adenomectomy and were usually transient. Diabetes insipidus is more frequent than hyponatremia. Diabetes insipidus usually occurs during the 1st postoperative day and resolves in the majority of cases within 10 days. In few patients, DI may persist and require therapy with ADH analogs. Hyponatremia usually occurs at the end of the 1st postoperative week and resolves in most cases within 5 days. Very few patients will need treatment other than fluid-intake restriction to avoid serious complications. Thus, careful monitoring of the WEDs in patients undergoing transsphenoidal pituitary adenoma surgery is mandatory for the first 10 postoperative days.

Endocrinological Outcome Following First Time Transsphenoidal Surgery for GH-, ACTH-, and PRL-Secreting Pituitary Adenomas

Summary.Background: To study remission rates and pituitary functions following transsphenoidal surgery of newly diagnosed GH-, ACTH-, and PRL-secreting pituitary adenomas.Methods: Out of a series of 329 newly diagnosed pituitary adenomas, 131 (39.8%) were hormone (67 GH-, 27 ACTH-, 37 PRL-) secreting. PRL-secreting adenomas were subjected to surgery because they failed to respond to previous medical treatment therapy. The data on secreting adenomas, regarding the results of standardised endocrinological testing, MRI findings and water metabolism disturbances, were extracted retrospectively from the pituitary data-base of the hospital. The mean follow-up was 3.7 years.Results: The overall remission rate for PRL-secreting adenomas (27%) was significantly lower than for GH- (71.6%) and ACTH-secreting (81.5%) ones. Remission rates correlated negatively with the magnitude of preoperative hormone excess (not in Cushings disease), tumour size (not in prolactinoma) and invasiveness. Generally, the improvement of the adenopituitary functions was statistically significant during the first three postoperative months, and thereafter remained unchanged. Diabetes insipidus persisting for more than three months occurred with similar frequency in the three patient groups (in 9.4% of GH-, in 6.7% of ACTH-, and in 10% of PRL-secreting adenomas). Tumour regrowths occurred more often in PRL-(20%) than in ACTH- (9.1%) and GH- (0%) secreting tumours.Conclusions: In GH- and ACTH-secreting pituitary adenomas, remission rates were significantly higher and recurrence rates lower than in PRL-secreting adenomas, which had failed to respond to previous medical therapy. The overall postoperative adenopituitary function was improved in all patient groups. Diabetes insipidus occurred with similar frequency in all patient groups. When reporting on results of surgery for secreting pituitary adenomas, not only remission and recurrence rates, but also the results of the pituitary function should be included.

Intraoperative preservation of corticospinal function in the brainstem

Background: The corticospinal tract features a largely exposed course through the brainstem, and is therefore at risk in many brainstem-related procedures. No large case series on motor-evoked potential (MEP) monitoring during brainstem surgery have been reported as yet. Objective: To understand intraoperative MEP changes during brainstem-related surgery, and to explore the value of MEP monitoring for preventing permanent new paresis. Methods: Myogenic MEPs after transcranial electrical train stimulation were monitored in 70 cases of intraparenchymal (n = 39) and extraparenchymal (n = 31) brainstem-related tumours and vascular lesions. MEP recordings failed in another five cases. Motor outcome and intraoperative MEP results were documented prospectively and correlated for this study. Results: Significant MEP changes occurred in 46% of cases. Stable and only reversibly deteriorated MEPs warranted unimpaired motor outcome (n = 50, 71% of all cases). Irreversible deterioration and reversible loss (n = 19, 27%) indicated a 37% risk for transient deficit. Irreversible loss (one case, 1.5%) predicted permanent paresis. MEPs and motor outcome correlated equally well in intra- and extraparenchymal lesions. Somatosensory-evoked potentials (SEPs) did not reliably reflect motor outcome. Permanent motor deficit occurred in one out five cases (20%) with failed MEP recordings. Conclusions: MEP monitoring—as opposed to SEPs—is a valid indicator of corticospinal function in brainstem-related surgery, independent from the type of lesion operated on. New deficit occurs only after more pronounced MEP changes than in supratentorial surgery, but complete loss as in spinal surgery is not required. MEPs may help to prevent permanent new paresis.

Intraoperative Neurophysiological Mapping and Monitoring for Supratentorial Procedures

Publisher Summary This chapter explores intraoperative neurophysiological mapping and monitoring for supratentorial procedures. The goal of delineation through mapping and monitoring of eloquent cortical areas and subcortical pathways is to achieve a more radical cytoreduction while still preserving unimpaired function. Somatosensory evoked potentials (SEPs) are typically elicited by the electrical bipolar stimulation of a peripheral nerve. The most commonly stimulated nerves are the median nerve, if sensory modalities and cortical regions representing the upper extremities are to be monitored, and the posterior tibial nerve for the lower extremities. SEP recording from these nerves is easiest to obtain and provides the most stable results. Neurophysiological mapping has corrected the presurgical estimation of the central sulcus location in 12% of patients. It also helps to identify the motor stimulation point for monitoring motor evoked potentials (MEPs). Intraoperative neurophysiological monitoring of the functional integrity of the cortical sensory and motor areas and pathways is noninvasive and does not interfere with the ongoing surgical procedure. It gives immediate feedback about functional impairment of the monitored structure. This provides the opportunity to rectify this impairment.

Stroke prevention during surgery for deep-seated gliomas

AIMS OF THE STUDY New motor deficit after surgery for deep-seated gliomas can occur from subcortical ischemia of the pyramidal tract. Motor evoked potentials (MEPs) validly indicate impending motor tract ischemia in cerebrovascular surgery. This study determines the feasibility and clinical utility of MEP monitoring for ischemic complication avoidance during surgery for deep-seated, specifically insular gliomas. METHODS MEPs were recorded during 100 operations of insular gliomas. Intraoperative MEP results were correlated with postoperative clinical and imaging results. RESULTS Useful MEP monitoring was possible in 89/100 cases, 88 of which were assessable since one patient died early postoperatively. Stable recordings warranted unimpaired motor outcome in 47/88 cases (53%). Surgical intervention reversed MEP attenuation in 26 of the remaining 41 cases (30% of the overall series) to prevent motor deficit except transient paresis in 12 (14%). Irreversible MEP changes without loss in eight cases (9%) resulted in only transient new deficit in seven cases, except one with permanent new paresis. Permanent paresis also occurred in seven cases (8%) where complete MEP loss could not be prevented. Permanent paresis arose exclusively through stroke of the deep motor pathways, whereas transient deficit typically corresponded to transitory ischemia of the pyramidal tract. MEP changes attributable to ischemic events frequently occurred spatially and temporally uncorrelated to resection in critical proximity of the motor tract. CONCLUSIONS Ischemia in deep-seated glioma surgery usually occurs uncorrelated to resection close to the pyramidal tract. MEP monitoring efficiently helps detect ischemia early and to avert definite stroke and permanent new paresis in part of these cases.

Continuous motor monitoring enhances functional preservation and seizure-free outcome in surgery for intractable focal epilepsy

PurposeComplete yet safe resection close to motor areas in medically intractable epilepsy requires functional information. New deficit may occur despite preservation of motor cortex, e.g., through vascular compromise. Here, we explore for the first time the feasibility, safety, and the clinical value of continuous motor-evoked potential (MEP) monitoring in focal epilepsy surgery.MethodsHigh-frequency stimulation for MEP monitoring was performed during 100 consecutive lesionectomies critically related to motor areas and pathways. Extraoperative motor cortex mapping was performed in 27 of these cases via chronically implanted subdural grid electrodes. MEP monitoring results, postoperative motor outcome, and seizure control were correlated in a prospective observational design.ResultsReliable MEP monitoring was achieved in 86 cases. Young age was the only discernible cause of unsuccessful recordings. Seizures from cortex stimulation did not occur. MEP changes (36%) predicted new motor deficit (17%) in all cases except purely cortical lesions. MEP changes predicted occurrence and permanence of new pareses. New deficit was significantly more frequent without (as compared with) successful monitoring (43% vs. 17%); permanently severe pareses from ischemia occurred only without MEPs (21% vs. 0%). Complete seizure control was significantly more frequent in successfully monitored cases (60% vs. 31%). Even with extraoperative motor mapping, severe paresis occurred only among cases with unsuccessful MEPs.ConclusionsContinuous MEP monitoring in epilepsy surgery is feasible and safe. It reflects motor function complementarily to the localizing motor mapping results. Successful MEP monitoring correlates with unimpaired motor outcome and full seizure control.

Does familiarity facilitate the cortical processing of music sounds

Automatic cortical sound discrimination, as indexed by the mismatch negativity (MMN) component of the auditory evoked potential, is facilitated for familiar speech sounds (phonemes). In musicians as compared to non-musicians, an enhanced MMN has been observed for complex non-speech sounds. Here, musically trained subjects were presented with sequences of either familiar (tonal) or structurally matched unfamiliar (atonal) triad chords, both with either fixed or randomly transposed chord root pitch. The MMN elicited by deviant chords did not differ for familiar and unfamiliar triad sequences, and was undiminished even to unfamiliar deviant sounds which were consciously undetectable. Only subsequent attention-related components indicated facilitated cognitive processing of familiar sounds, corresponding to higher behavioral detection scores.