Tag: Intraoperative neuromonitoring

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Historical evolution of microvascular decompression after Jannetta’s establishment: Anatomical maps and physiological compasses—a narrative review

Acta Neurochirurgica (2026) 168:74

This narrative review chronicles five decades of refinement in microvascular decompression (MVD) for trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia, tracing developments from Jannetta’s microsurgical breakthrough to contemporary practice. It emphasizes evolving microsurgical anatomy, tailored craniotomies, endoscopic/exoscopic visualization, and nuanced decompression techniques such as noncompressive transposition versus prosthetic interposition.

The article also highlights operative support advances—high-resolution MRI/MRA, virtual simulation, and intraoperative neuromonitoring (BAEP, LSR)—as physiological “compasses” that improve safety and outcome durability. Together, anatomical “maps” and physiological feedback frame current standards and ongoing challenges in achieving long-term, biologically harmonious decompression.

Microvascular Decompression (MVD) Evolution: MVD has developed from Jannetta’s original microsurgical demonstration of vascular compression into a safe, durable, and standardized surgical treatment for neurovascular compression syndromes, especially trigeminal neuralgia (TN), hemifacial spasm (HFS), and glossopharyngeal neuralgia (GPN).

Anatomical Foundations: Detailed microsurgical anatomy, including the “Rule of Three” for the cerebellopontine angle (CPA), enables tailored, minimally invasive approaches and underpins the understanding of neurovascular conflicts and surgical route selection.

Tailored Surgical Approaches: Three individualized approaches—lateral supracerebellar-infratentorial for TN, infrafloccular for HFS, and transcondylar fossa for GPN—minimize cerebellar retraction and optimize decompression, improving safety and efficacy.

Decompression Strategies: Techniques have shifted from prosthetic interposition (placing a material between vessel and nerve) to noncompressive transposition (mobilizing and securing the vessel away from the nerve), with evidence supporting better long-term outcomes for transposition.

Visualization and Simulation Advances: The integration of endoscopic/exoscopic systems, neuronavigation, and virtual simulation has enhanced visualization, surgical precision, and education, extending the original ethos of microscopic surgery.

Intraoperative Monitoring: Real-time monitoring using brainstem auditory evoked potentials (BAEPs) and lateral spread response (LSR) on facial EMG helps avoid complications and assess decompression adequacy, significantly reducing postoperative morbidity.

Role of Imaging: High-resolution MRI and MRA now routinely identify neurovascular compression preoperatively, though imaging findings are considered supportive rather than diagnostic due to limited specificity in low-grade conflicts.

Sustained First-Line Role: Despite advances in radiosurgery and pharmacotherapy, MVD remains the first-line surgical option for appropriately selected patients, due to its proven long-term efficacy and safety.

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Neuroapraxia of Trigeminal Nerve Controlled by Neuromonitoring During Microvascular Decompression in Multiple Sclerosis Patients Affected by Drug-Resistant Trigeminal Neuralgia Recurrent After Previous Operations

Operative Neurosurgery 29:295–300, 2025

This case series reports the first use of intraoperative neuromonitoring-controlled neuroapraxia of the trigeminal nerve with a temporary aneurysm clip during microvascular decompression for drug-resistant, recurrent trigeminal neuralgia in multiple sclerosis patients, showing immediate pain relief and no complications at up to 10 months’ follow-up.

• Trigeminal neuralgia (TN) in multiple sclerosis (MS) patients is difficult to treat and often recurs after surgery.

• This report describes the first 3 cases of recurrent, drug-resistant MS-related TN treated with intraoperative neuromonitoring (IONM)-controlled neuroapraxia during microvascular decompression (MVD).

• Neuroapraxia was induced by applying a temporary titanium aneurysm clip to the trigeminal nerve for up to 30 seconds, with real-time IONM to avoid nerve damage.

• All patients achieved immediate pain relief and maintained Barrow Neurological Institute pain score I at 9–10 months follow-up, with no major complications.

• Compared to previous techniques, this approach minimized complications by reducing clip time and using neuromonitoring.

• This technique may offer a safe, promising option for MS patients with recurrent TN, but larger studies with longer follow-up are needed.

• The study’s main limitation is the small patient number and short follow-up period.

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Dorsal column mapping in resection of intramedullary spinal cord tumors: a prospective comparison of two methods and neurological follow‑up

Acta Neurochirurgica (2023) 165:3493–3504

In surgery for intramedullary spinal cord tumors (imSCT), distortion of the anatomy challenges the visual identification of dorsal columns (DC) for midline myelotomy. Dorsal column mapping (DCM) and spinal cord stimulation (SCS) can identify DC neurophysiologically. We compare application and feasibility of both methods.

Methods Patients with surgically treated imSCT were prospectively included between 04/2017 and 06/2019. The anatomical midline (AM) was marked. SSEPs at the DC after stimulation of tibial/median nerve with an 8-channel DCM electrode and cortical SSEP phase reversal at C3/C4 after SCS using a bipolar concentric probe were recorded. Procedural and technical aspects were compared. Standardized neurological examinations were performed preoperatively, 1 week postoperatively and after more than 12 months.

Results The DCM electrode detected the midline in 9/13 patients with handling limitations in the remaining patients. SCS was applicable in all patients with determination of the midline in 9/13. If both recordings could be acquired (6/13), concordance was 100%. If baseline SSEPs were poor, both methods were limited. SCS was less time-consuming (p = 0.001), cheaper, and easier to handle. In 92% of cases, the AM and neurophysiologic midlines were concordant. After myelotomy, 3 patients experienced > 50% reduction in amplitude of SSEPs. Despite early postoperative worsening of DC function, longterm follow-up showed significant recovery and improvement in quality of life.

Conclusion DCM and SCS may help confirm and correct the AM for myelotomy in imSCT, leading to a favorable longterm neurological outcome in this cohort. SCS evolved to be superior concerning applicability, cost-effectiveness, and time expenditure.

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Intraoperative MRI–based elastic fusion for anatomically accurate tractography of the corticospinal tract

Neurosurg Focus 50 (1):E9, 2021

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.

METHODS 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.

RESULTS 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.

CONCLUSIONS The present study shows that tractography after IBEF accurately correlates with IONM and patient outcomes and thus demonstrates reliability in this initial study.

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Continuous subcortical motor evoked potential stimulation using the tip of an ultrasonic aspirator for the resection of motor eloquent lesions

Continuous subcortical motor evoked potential stimulation

J Neurosurg 123:301–306, 2015

Resection of a motor eloquent lesion has become safer because of intraoperative neurophysiological monitoring (IOM). Stimulation of subcortical motor evoked potentials (scMEPs) is increasingly used to optimize patient safety. So far, scMEP stimulation has been performed intermittently during resection of eloquently located lesions. Authors of the present study assessed the possibility of using a resection instrument for continuous stimulation of scMEPs.

Methods An ultrasonic surgical aspirator was attached to an IOM stimulator and was used as a monopolar subcortical stimulation probe. The effect of the aspirator’s use at different ultrasound power levels (0%, 25%, 50%, 75%, and 100%) on stimulation intensity was examined in a saline bath. Afterward monopolar stimulation with the surgical aspirator was used during the resection of subcortical lesions in the vicinity of the corticospinal tract in 14 patients in comparison with scMEP stimulation via a standard stimulation electrode. During resection, the stimulation current at which an MEP response was still measurable with subcortical stimulation using the surgical aspirator was compared with the corresponding stimulation current needed using a standard monopolar subcortical stimulation probe at the same location.

Results The use of ultrasound at different energy levels did result in a slight but irrelevant increase in stimulation energy via the tip of the surgical aspirator in the saline bath. Stimulation of scMEPs using the surgical aspirator or monopolar probe was successful and almost identical in all patients. One patient developed a new permanent neurological deficit. Transient new postoperative paresis was observed in 28% (4 of 14) of cases. Gross-total resection was achieved in 64% (9 of 14) cases and subtotal resection (> 80% of tumor mass) in 35% (5 of 14).

Conclusions Continuous motor mapping using subcortical stimulation via a surgical aspirator, in comparison with the sequential use of a standard monopolar stimulation probe, is a feasible and safe method without any disadvantages. Compared with the standard probe, the aspirator offers continuous information on the distance to the corticospinal tract.

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Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors

Continuous dynamic subcortical mapping

J Neurosurg 120:1015–1024, 2014

The authors developed a new mapping technique to overcome the temporal and spatial limitations of classic subcortical mapping of the corticospinal tract (CST). The feasibility and safety of continuous (0.4–2 Hz) and dynamic (at the site of and synchronized with tissue resection) subcortical motor mapping was evaluated.

Methods. The authors prospectively studied 69 patients who underwent tumor surgery adjacent to the CST (< 1 cm using diffusion tensor imaging and fiber tracking) with simultaneous subcortical monopolar motor mapping (short train, interstimulus interval 4 msec, pulse duration 500 μsec) and a new acoustic motor evoked potential alarm. Continuous (temporal coverage) and dynamic (spatial coverage) mapping was technically realized by integrating the mapping probe at the tip of a new suction device, with the concept that this device will be in contact with the tissue where the resection is performed. Motor function was assessed 1 day after surgery, at discharge, and at 3 months.

Results. All procedures were technically successful. There was a 1:1 correlation of motor thresholds for stimulation sites simultaneously mapped with the new suction mapping device and the classic fingerstick probe (24 patients, 74 stimulation points; r2 = 0.98, p < 0.001). The lowest individual motor thresholds were as follows: > 20 mA, 7 patients; 11–20 mA, 13 patients; 6–10 mA, 8 patients; 4–5 mA, 17 patients; and 1–3 mA, 24 patients. At 3 months, 2 patients (3%) had a persistent postoperative motor deficit, both of which were caused by a vascular injury. No patient had a permanent motor deficit caused by a mechanical injury of the CST.

Conclusions. Continuous dynamic mapping was found to be a feasible and ergonomic technique for localizing the exact site of the CST and distance to the motor fibers. The acoustic feedback and the ability to stimulate the tissue continuously and exactly at the site of tissue removal improves the accuracy of mapping, especially at low (< 5 mA) stimulation intensities. This new technique may increase the safety of motor eloquent tumor surgery.

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Predictive Value and Safety of Intraoperative Neurophysiological Monitoring With Motor Evoked Potentials in Glioma Surgery

Neurosurgery 70:1060–1071, 2012 DOI: 10.1227/NEU.0b013e31823f5ade

Resection of gliomas in or adjacent to the motor system is widely performed with intraoperative neuromonitoring (IOM). Despite the fact that data on the safety of IOM are available, the significance and predictive value of the procedure are still under discussion. Moreover, cases of false-negative monitoring affect the surgeon’s confidence in IOM.

OBJECTIVE: To examine cases of false-negative IOM to reveal structural explanations.

METHODS: Between 2007 and 2010, we resected 115 consecutive supratentorial gliomas in or close to eloquent motor areas using direct cortical stimulation for monitoring of motor evoked potentials (MEPs). The monitoring data were reviewed and related to new postoperative motor deficit and postoperative imaging. Clinical outcomes were assessed during follow-up.

RESULTS: Monitoring of MEPs was successful in 112 cases (97.4%). Postoperatively, 30.3% of patients had a new motor deficit, which remained permanent in 12.5%. Progression- free follow-up was 9.7 months (range, 2 weeks-40.6 months). In 65.2% of all cases, MEPs were stable throughout the operation, but 8.9% showed a new temporary motor deficit, whereas 4.5% (5 patients) presented with permanently deteriorated motor function representing false-negative monitoring at first glance. However, these cases were caused by secondary hemorrhage, ischemia, or resection of the supplementary motor area.

CONCLUSION: Continuous MEP monitoring provides reliable monitoring of the motor system, influences the course of operation in some cases, and has to be regarded as the standard for IOM of the motor system. In our series, we found no false-negative MEP results.

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Motor-evoked potentials (MEP) during brainstem surgery to preserve corticospinal function

Acta Neurochir (2011) 153:1753–1759. DOI 10.1007/s00701-011-1065-7

Brainstem surgery bears a risk of damage to the corticospinal tract (CST). Motor-evoked potentials (MEPs) are used intraoperatively to monitor CST function in order to detect CST damage at a reversible stage and thus impede permanent neurological deficits. While the method of MEP is generally accepted, warning criteria in the context of brainstem surgery still have to be agreed on.

Method We analyzed 104 consecutive patients who underwent microsurgical resection of lesions affecting the brainstem. Motor grade was documented prior to surgery, early postoperatively and at discharge. A baseline MEP stimulation intensity threshold was defined and intraoperative testing aimed to keep MEP response amplitude constant. MEPs were considered deteriorated and the surgical team was notified whenever the threshold was elevated by ≥20 mA or MEP response fell under 50%.

Findings On the first postoperative day, 18 patients experienced new paresis that resolved by discharge in 11. MEPs deteriorated in 39 patients, and 16 of these showed new postoperative paresis, indicating a 41% risk of new paresis. In the remaining 2/18 patients, intraoperative MEPs were stable, although new paresis appeared postoperatively. In one of these patients, intraoperative hemorrhage caused postoperative swelling, and the new motor deficit persisted until discharge. Of all 104 patients, 7 deteriorated in motor grade at discharge, 92 remained unchanged, and 5 patients have improved.

Conclusions Adjustment of surgical strategy contributed to good motor outcome in 33/39 patients. MEP monitoring may help significantly to prevent motor deficits during demanding neurosurgical procedures on the brainstem.

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