Simultaneous combination of electromagnetic navigation with visual evoked potential in endoscopic transsphenoidal surgery: clinical experience and technical considerations

Learning Curve for Endoscopic Transsphenoidal Surgery: A Systematic Review and Meta-Analysis

BACKGROUND

Endoscopic transsphenoidal surgery (ETSS) is emerging as an effective, minimally invasive surgery technique for brain tumors of the pituitary fossa. Using a surgical endoscope, surgeons can obtain a broader, nearer, and more apparent visual field with minimal keyhole entrance. However, ETSS may require a steep learning curve to achieve technical competence and relevant outcomes. Moreover, there is no consensus on the learning process of ETSS. We aimed to review and determine the technical proficiency points of ETSS and discuss how to accelerate the learning curve.

METHODS

Core databases, including PubMed, Embase, and the Cochrane Library, were systematically searched for learning curve studies that demonstrated the clinical outcomes and learning status of ETSS for pituitary adenomas using numerical data. Quality assessments of the included articles were performed using the Newcastle-Ottawa scale. The cutoff points were evaluated based on various outcome measures.

RESULTS

Eleven full-text articles, representing 2780 cases, were selected from 317 screened studies. The outcome measures were operative time, tumor removal, endocrinological results, visual field, and surgical complications. The plateaus or cutoff points in the learning curve varied with a mean of 103 ± 139.43 (range, 9-500) cases.

CONCLUSIONS

ETSS is an efficient and minimally invasive alternative surgical option for pituitary tumors. Plateau points may differ according to outcome measures, patient selection, training status, and surgical conditions. Therefore, great care should be taken when interpreting the learning curve. A systematic training program is essential to improve the learning process of endoscopic neurosurgical procedures.

Reliability of intraoperative visual evoked potentials (iVEPs) in monitoring visual function during endoscopic transsphenoidal surgery

OBJECTIVE

To refine a reliable and reproducible intraoperative visual evoked potentials (iVEPs) monitoring protocol during endoscopic transsphenoidal surgery. To assess the reliability of baseline iVEPs in predicting preoperative visual status and perioperative iVEP variation in predicting postoperative visual outcome.

METHODS

Sixty-four patients harboring tumors of the pituitary region were included. All patients underwent endoscopic endonasal approach (EEA) with iVEPs monitoring, using a totally intravenous anesthetic protocol. Ophthalmological evaluation included visual acuity and visual field studies.

RESULTS

Preoperatively, visual acuity was reduced in 86% and visual field in 76.5% of cases. Baseline iVEPs amplitude was significantly correlated with preoperative visual acuity and visual field (p = 0.001 and p = 0.0004, respectively), confirming the reliability of the neurophysiological/anesthetic protocol implemented. Importantly, perioperatively the variation in iVEPs amplitude was significantly correlated with the changes in visual acuity (p < 0.0001) and visual field (p = 0.0013). ROC analysis confirmed that iVEPs are an accurate predictor of perioperiative visual acuity improvement, with a 100% positive predictive value in patients with preoperative vision loss.

CONCLUSIONS

iVEPs during EEA is highly reliable in describing preoperative visual function and can accurately predict postoperative vision improvement.

SIGNIFICANCE

iVEPs represent a promising resource for carrying out a more effective and safe endoscopic transsphenoidal surgery.

Comparison Between Conventional Flash and Off-Response Intraoperative Visual Evoked Potential Monitoring for Endoscopic Endonasal Surgery

BACKGROUND

Intraoperative flash stimulation visual evoked potential (VEP) monitoring has been used for endoscopic endonasal approach (EEA). Recently, off-response VEP, which is recorded when the light stimulus is turned off, was introduced to monitor visual function intraoperatively.

OBJECTIVE

To evaluate off-response VEP monitoring in comparison with the conventional flash stimulation VEP monitoring for EEA.

METHODS

From March 2015 to March 2020, 70 EEA surgeries with intraoperative VEP monitoring (140 eyes) were performed. Light stimuli were delivered by a pair of goggle electrodes. Recording electrodes were placed on the scalp over the occipital region. The warning signal was prompted by a reduction of the peak-to-peak amplitude of the VEP by more than 50% compared to the initial amplitude. Visual function was assessed pre- and postoperatively. Results of flash and off-response VEP monitoring were compared.

RESULTS

VEP was recorded in 134 eyes. Warning signal occurred in 23 eyes (transient in 17 eyes and permanent in 6 eyes). Two eyes showed permanent VEP attenuation for flash VEP monitoring, in which one patient had postoperative visual function deterioration. Four eyes showed permanent VEP attenuation for off-response VEP monitoring, where 2 patients had postoperative visual function deterioration. Sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 98.9%, 50%, and 100%, respectively, for flash stimulation VEP, and 100%, 97.8%, 50%, and 100%, respectively, for off-response VEP.

CONCLUSION

VEP monitoring was useful to monitor visual function in EEA surgery. Off-response VEP monitoring was not inferior to conventional flash stimulation VEP monitoring.

Intraoperative monitoring of visual evoked potentials in patients undergoing transsphenoidal surgery for pituitary adenoma: a systematic review

BACKGROUND

Transsphenoidal surgery is the gold standard for pituitary adenoma resection. Although rare, a serious complication of surgery is worsened vision post-operatively.

OBJECTIVE

To determine whether, in patients undergoing transsphenoidal surgery for pituitary adenoma, intraoperative monitoring of visual evoked potentials (VEP) is a safe, reproducible, and effective technological adjunct in predicting postoperative visual function.

METHODS

The PubMed and OVID platforms were searched between January 1993 and December 2020 to identify publications that (1) featured patients undergoing transsphenoidal surgery for pituitary adenoma, (2) used intraoperative optic nerve monitoring with VEP and (3) reported on safety or effectiveness. Reference lists were cross-checked and expert opinion sought to identify further publications.

RESULTS

Eleven studies were included comprising ten case series and one prospective cohort study. All employed techniques to improve reliability. No safety issues were reported. The only comparative study included described a statistically significant improvement in post-operative visual field testing when VEP monitoring was used. The remaining case-series varied in conclusion. In nine studies, surgical manipulation was halted in the event of a VEP amplitude decrease suggesting a widespread consensus that this is a warning sign of injury to the anterior optic apparatus.

CONCLUSIONS

Despite limited and low-quality published evidence regarding intra-operative VEP monitoring, our review suggests that it is a safe, reproducible, and increasingly effective technique of predicting postoperative visual deficits. Further studies specific to transsphenoidal surgery are required to determine its utility in protecting visual function in the resection of complex pituitary tumours.

Electromagnetic Navigation Systems and Intraoperative Neuromonitoring: Reliability and Feasibility Study

BACKGROUND

A recent influx of intraoperative technology is being used in neurosurgery, but few reports investigate the accuracy and safety of these technologies when used simultaneously.

OBJECTIVE

To assess the ability to use an electromagnetic navigation system alongside multimodal intraoperative neurophysiological monitoring (IONM).

METHODS

Single-institution prospective cohort study of patients requiring craniotomy for brain tumor resection operated using an electromagnetic navigation system (AxiEM, Medtronic®). motor evoked potentials, somatosensory evoked potentials (SSEPs), electroencephalography, and electromyography were recorded and analyzed with AxiEM on (with/without filters) and off. The neurological outcomes of the patients were recorded.

RESULTS

A total of 15 patients were included (8 males/7 females, mean age 52.13 yr). Even though the raw acquisition is affected by the electromagnetic field (particularly SSEPs), no significant difference was detected in the morphology, amplitude, and latency of the different monitoring modalities (AxiEM off vs on) after the appropriate software filter application. Adjustments to the frequency of SSEP stimulation and number of averages, and reductions to the low-pass filters were applied. Notch filters were used appropriately and changes to the physical setup of the IONM and electromagnetic navigation system equipment reduced noise. Postoperatively, none of the patients developed new focal deficits; 7 patients showed improvement in their motor deficit (4 recovered fully).

CONCLUSION

The information provided by the IONM in intracranial neurosurgery patients whilst also using electromagnetic navigation systems is reliable for monitoring, mapping, and detecting intraoperative complications, provided that the appropriate software filters and tools are applied.

Automatic robot-world calibration in an optical-navigated surgical robot system and its application for oral implant placement

PURPOSE

Robot-world calibration, used to precisely determine the spatial relation between optical tracker and robot, is regarded as an essential step for optical-navigated surgical robot system to improve the surgical accuracy. However, these methods are complicated with numerous computation. Therefore, a more efficient method of a robot-world calibration is necessary.

METHODS

A fully automatic robot-world calibration was proposed and applied in a surgical robot system for oral implant placement. Making full usage of the movement characteristics of a tandem robot, the least square fitting algorithm was implemented to calculate the relationship between the tool center point of the robot and the robot reference frame, with the robot-world calibration matrix obtained as result.

RESULTS

The experiment was designed to verify the accuracy of the robot-world calibration. The average distance deviation was 1.11 mm, and the average angle deviation was 0.99°. From the animal experiment on the pig maxilla, the entry, apical and angle deviation of the surgical robot system were 1.44 ± 1.01 mm, 1.68 ± 0.76 mm, 1.01 ± 1.06°, respectively.

CONCLUSION

The surgical robot system for oral implant placement with our robot-world calibration maintains a high precision. Besides, the operation range of the surgical tool is no longer limited by the visual range of the optical tracking device. Hence, it is unnecessary to adjust the optical tracking device for the planned implant trajectories to different positions and directions.

Extended endoscopic endonasal resection of craniopharyngioma using intraoperative visual evoked potential monitoring: technical note

BACKGROUND

To avoid deterioration of visual function, extended endoscopic endonasal transsphenoidal surgery (TSS) for craniopharyngioma was performed with visual evoked potential (VEP) monitoring using light-emitting diodes (LEDs).

METHODS

The position of the optic chiasm was carefully evaluated on the preoperative midsagittal magnetic resonance (MR) images. Intraoperatively, direct and sharp dissection of the tumor from the optic chiasm was performed under VEP monitoring with LEDs through extended endoscopic endonasal TSS. If the VEP finding changed and became unstable, the operator were informed and stopped the surgical manipulation for the optic chiasm to recover. After 5-10 min, recovery of VEP findings was checked and the procedure resumed.

RESULTS

Extended endoscopic endonasal TSS with VEP monitoring was performed in consecutive 7 adult patients with newly diagnosed suprasellar craniopharyngiomas with maximum diameters of 25-41 mm (mean 33.7 mm). VEPs were stable throughout the surgery in 5 cases, but showed temporary instability and amplitude decrease in 2 cases, although the VEPs had recovered at the end of the surgery. Visual function, evaluated using visual impairment score, was improved after surgery in all patients. Gross total removal was achieved in 5 cases, and subtotal removal (90%) in 2 cases.

CONCLUSIONS

Intraoperative VEP monitoring is the only way to test visual function during surgery, and may be important and helpful in extended endoscopic endonasal TSS, which requires direct dissection between the optic nerve and craniopharyngioma under the endoscope.

Delayed postoperative hyponatremia after endoscopic transsphenoidal surgery for pituitary adenoma

BACKGROUND

Hyponatremia generally occurs after transsphenoidal surgery (TSS) in a delayed fashion. Most patients with delayed postoperative hyponatremia (DPH) are asymptomatic or only express non-specific symptoms; consequently, DPH is associated with prolonged hospitalization. No consensus has been reached on which patients are at greatest risk of developing DPH. We reviewed patients with DPH and evaluated predictive factors for DPH.

METHODS

We retrospectively analyzed 107 consecutive patients who underwent endoscopic TSS for pituitary adenoma (January 2010-December 2016). Patients with DPH (hyponatremia group) and without DPH (normonatremia group) were compared according to their nadir sodium levels on postoperative days 3 to 10. We documented the patients' demographics, clinical features, and postoperative physiological characteristics.

RESULTS

Twenty-five (23.4%) patients developed DPH after endoscopic TSS. The patients' mean age was 54 ± 17 years, and 63.6% of the patients were female. The overall prevalence of DPH was 23.4%. The non-parametric χ2 test and the Mann-Whitney U test revealed statistically significant differences in age, use of antihypertensive drugs, nonfunctioning pituitary adenoma, and higher yet normal preoperative thyroid-stimulating hormone level between the hyponatremia and normonatremia groups (P < 0.05). Logistic regression analysis revealed that only older age was a useful independent predictive factor for DPH (odds ratio, 1.05; 95% confidence interval, 1.01-1.08; P = 0.01). The serum sodium levels on postoperative day 2 were significantly lower in the hyponatremia than normonatremia group (P < 0.01) and were negatively correlated with age (r = - 0.25, P < 0.05). The cut-off age for predicting DPH was 55 years. The hospital stay was significantly longer in the hyponatremia than normonatremia group (P < 0.01).

CONCLUSIONS

Age of more than 55 years was an independent predictive factor for DPH even after adjusting for potential confounders. Older age was negatively correlated with the serum sodium level on postoperative day 2. Preventing early decreases in the sodium level could reduce the risk of DPH.

TRIAL REGISTRATION

1707-027.

The Predictive Role of Intraoperative Visual Evoked Potentials in Visual Improvement After Endoscopic Pituitary Tumor Resection in Large and Complex Tumors: Description and Validation of a Method

BACKGROUND

With the advent of extensive endoscopic approaches for pituitary tumors, there has also been an increase in surgery for larger and more complex tumors. Intraoperative manipulation during endoscopic resection of sellar tumors poses potential risk in postoperative visual function in this tumor population. This study proposes a method of accurate intraoperative monitoring of visual evoked potentials (VEPs) and its role in predicting visual function outcomes.

METHODS

Intraoperative VEPs were monitored for 42 resections from a single surgical team, with average tumor size of 2.84 cm. Changes in VEP amplitude and latency in excess of 50% were considered significant. Preoperative and postoperative visual information was obtained from ophthalmology and hospital records, along with patient demographics, comorbidities, and tumor characteristics.

RESULTS

Patients were stratified as experiencing deteriorations in VEPs that did not restore to baseline (n = 4), deteriorations in VEPs that did restore to baseline (n = 6), no change in VEPs (n = 31), and improvement in VEPs (n = 1). Correlation between VEP changes and postoperative visual fields was measured through univariate ordered logistic regression. Improved intraoperative VEP measurements were associated with odds ratio (OR) of visual field improvement of 3.15 (95% confidence interval, 1.15-8.59). Specifically, changes in VEP amplitude were positively associated with visual field improvement with OR of 4.35 (OR, 1.29-14.7). No association was observed between VEPs and other patient or tumor characteristics.

CONCLUSION

Changes in VEP amplitude during endoscopic sellar tumor resection correlate with postoperative visual function. Intraoperative VEP monitoring can serve an important role in preventing postoperative visual field loss.