An investigation into quality of life improvement in patients undergoing microvascular decompression for hemifacial spasm

Decompression Surgery in Elderly Patients with Hemifacial Spasm Refractory to Botulinum Toxin

BACKGROUND

Botulinum toxin is an effective treatment for hemifacial spasm in elderly patients. However, some patients do not tolerate the side effects and frequency of botulinum toxin treatments.

OBJECTIVES

The purpose of this study was to evaluate the characteristics and outcomes of a cohort of elderly patients referred by neurologists for surgical decompression of the facial nerve following botulinum toxin treatment.

METHODS

In a prospective cohort study, logistic regression was used to detect potential predictors of spasm-freedom after surgical decompression of the facial nerve in elderly patients that received ≤8 and >8 botulinum toxin treatments for hemifacial spasm before surgery. Age, sex, side, preoperative symptom duration, and preoperative botulinum toxin treatment were assessed as potential predictors of spasm-freedom at last follow-up.

RESULTS

Of 76 elderly patients with hemifacial spasm treated with botulinum toxin and microvascular decompression, with at least 2-years of follow-up (median, 44.5 months), 84.2% were spasm-free at last follow-up. Age (P = 0.38), sex (P = 0.59), side (P = 0.15), preoperative symptom duration (P = 0.7), and number of preoperative botulinum toxin treatments (P = 0.3) were not predictors of long-term spasm-freedom. Permanent ipsilateral hearing loss was the most frequent complication (3.9%).

CONCLUSION

This study provides evidence that elderly patients can undergo botulinum toxin treatment for hemifacial spasm without compromising their likelihood of achieving spasm-freedom with future surgical decompression. Therefore, surgical decompression of the facial nerve is an effective therapy for elderly patients with hemifacial spasm refractory to botulinum toxin.

White matter structural changes before and after microvascular decompression for hemifacial spasm

Hemifacial spasm (HFS) is a syndrome characterized by involuntary contractions of the facial muscles innervated by the ipsilateral facial nerve. Currently, microvascular decompression (MVD) is an effective treatment for HFS. Diffusion weighted imaging (DWI) is a non-invasive advanced magnetic resonance technique that allows us to reconstruct white matter (WM) virtually based on water diffusion direction. This enables us to model the human brain as a complex network using graph theory. In our study, we recruited 32 patients with HFS and 32 healthy controls to analyze and compare the topological organization of whole-brain white matter networks between the groups. We also explored the potential relationships between altered topological properties and clinical outcomes. Compared to the HC group, the white matter network was disrupted in both preoperative and postoperative groups of HFS patients, mainly located in the somatomotor network, limbic network, and default network (All P < 0.05, FDR corrected). There was no significant difference between the preoperative and postoperative groups (P > 0.05, FDR corrected). There was a correlation between the altered topological properties and clinical outcomes in the postoperative group of patients (All P < 0.05, FDR corrected). Our findings indicate that in HFS, the white matter structural network was disrupted before and after MVD, and that these alterations in the postoperative group were correlated with the clinical outcomes. White matter alteration here described may subserve as potential biomarkers for HFS and may help us identify patients with HFS who can benefit from MVD and thus can help us make a proper surgical patient selection.

Safety and efficacy of endoscope-assisted versus microscopic microvascular decompression surgery for hemifacial spasm: a prospective cohort study

Microscopic microvascular decompression (M-MVD) is a classical treatment for relieving long-term hemifacial spasms (HFS). An endoscopy technique has recently been introduced to improve M-MVD; however, this application remains debatable. This study compared the safety and effectiveness of endoscope-assisted microvascular decompression (EA-MVD) and M-MVD for HFS. From February 2021 to September 2022, we enrolled 49 patients with HFS assigned to the EA-MVD (n = 26) and M-MVD (n = 23) groups. The patients were assessed with Park YS grades, operative time, hospital days, and complications. Evaluations were performed in the early postoperative period, at one month, 3 months, 6 months, and at least 12 months. Twenty-three (23/26, 88.5%) patients in the EA-MVD group and 20 (20/23, 87.0%) patients in the M-MVD group achieved spasm-free relief, ranging over "excellent" and "good" Park YS grades. The operative time in the EA-MVD and M-MVD groups were 143 ± 28 min and 145 ± 22 min (p = 0.002). The duration of hospital stay was 6.8 ± 0.8 days and 7.2 ± 1.3 days in the EA-MVD and M-MVD groups (p = 0.002), respectively. All surgeries for HFS were successful, with no death, stroke, hearing loss, facial numbness, or other extreme complications. In conclusion, EA-MVD, compared with M-MVD, demonstrated equally effective outcomes with decreased operative time and hospital stays, providing bright intraoperative illumination and flexible surgical vision.

Objective demonstration of eyelid spasm relief with smartphone and custom software in hemifacial spasm patients

PURPOSE

To objectively demonstrate eyelid spasms relief in hemifacial spasm (HFS) patients using a smartphone and a custom-made software.

METHODS

Nineteen patients with HFS had standardized videos recorded with a smartphone (iPhone 6S, Apple) camera before and 15 days after receiving onabotulinumtoxinA injections. Nineteen age-matched control subjects were also assessed. The Eye Aspect Ratio (EAR) is an algorithm previously described to determine whether the eye is opened or closed. When the eye is closed, EAR tends to be closer to zero. Analogously, if the eye is wide open, values are greater. A custom-made software using the EAR concept was developed and pre- and post-treatment EARs were analyzed to assess HFS patients.

RESULTS

Botulinum toxin (BoNT) injections led to a significant increase in the average EAR of the affected side: + 10.4% (p = 0.0175) of HFS patients, compared to baseline. Mean EAR before BoNT applications were significantly lower (16.2%) on the affected side (0.25 ± 0.05) of HFS patients when compared to controls (0.30 ± 0.05, p = 0.004). After BoNT injections, no statistically significant difference was observed for the average EAR between the affected side of HFS patients (0.27 ± 0.04) and controls (p = 0.20).

CONCLUSIONS

Use of a smartphone and custom-made software objectively demonstrated eyelid spasm relief in patients with HFS. Additional refinement of this system could permit more accurate assessments of treatment response rates for each patient, making it possible to be used in clinical practice.

Predictors of Multi-Vessel Identification, Outcome, and Optimal Surgical Timing for Microvascular Decompression in Hemifacial Spasm

OBJECTIVES AND BACKGROUND

Hemifacial spasm (HFS) is a disabling condition that imposes significant burden upon patients. Microvascular decompression (MVD) surgery is the most effective and long-lasting treatment for HFS, but outcomes following this surgery may vary based on a variety of clinical and operative factors. A more thorough understanding of the variables that impact patient outcome after MVD surgery is needed.

METHODS

A systematic review and meta-analysis of Medline, Embase, and Central was conducted (n = 2108 screened; n = 86 included) with the goal of determining the impact of the following variables on outcome: duration of disease, geographic location, intraoperative use of an endoscope, and intraoperative finding of single versus multi-vessel neurovascular compression.

RESULTS

Most cases of hemifacial spasm occur on the left side (53.9%, p < 0.001) and are more common in women than men (66.5% versus 33.5%, p < 0.0001). The offending vessel frequencies were: 40.8% anterior inferior cerebellar artery [AICA], 24.9% posterior inferior cerebellar artery [PICA], 17.2% multiple vessels, and 4.7% vertebral artery [VA]. Multiple vessel combinations involved: 26.5% PICA + AICA, 24.6% PICA + VA, 23.1% AICA + VA, and 4.7% AICA + PICA + VA. Relative to the Americas, AICA was less frequent in Europe (p = 0.005), while PICA more frequent in Europe (p = 0.009) and Asia (p < 0.0001). With endoscope assistance, frequency of multiple vessels identified was 31.7% (versus 14.7% with non-endoscopic, p = 0.005), and 27.4% for AICA (43.5% with non-endoscopic, p = 0.003). Spasm improvement was 94.1% near discharge and 96.0% at maximum follow-up. Complications occurred in 16.5% of cases, with spasm recurrence in 2.4%. Greatest frequency of spasm improvement (p < 0.0001) and lowest spasm recurrence rates (p = 0.0005) were reported in series from Asia. For every additional month of pre-operative spasm, the effect size of post-operative improvement decreased (p = 0.04). With every subsequent postoperative month, the effect size of spasm improvement increased (p = 0.0497). The frequency of spasm improvement was significantly higher in series published after 2005 (94.4% versus 97.4%, p = 0.005).

CONCLUSION

Clinical outcomes following MVD for HFS have improved since 2005. Consideration should be given to earlier operation (shorter disease duration) and use of an endoscope may increase detection of multiple offending vessels. Further studies are needed to understand regional differences in culprit vessel incidence and surgical outcomes in the Americas, Europe, and Asia.

Intraoperative Monitoring of the Facial Nerve during Microvascular Decompression for Hemifacial Spasm

This review article discusses the clinical significance of intraoperative neurophysiological monitoring (IONM), provides recommendations for monitoring protocols, and considers the interpretation of results in microvascular decompression (MVD) for hemifacial spasm (HFS). The lateral spread response (LSR) is an important monitoring parameter during MVD. It helps to identify the responsible blood vessel and confirms its thorough decompression from the facial nerve. The disappearance of the LSR during surgery is associated with favorable clinical outcomes. Standard and revised monitoring protocols and the confirmation of LSR persistence and disappearance are also discussed. The blink reflex and other facial nerve monitoring modalities, such as free-running electromyography, facial motor evoked potentials, F-waves, and the Z-L response, are further considered.

Applying a deep convolutional neural network to monitor the lateral spread response during microvascular surgery for hemifacial spasm

BACKGROUND

Intraoperative neurophysiological monitoring is essential in neurosurgical procedures. In this study, we built and evaluated the performance of a deep neural network in differentiating between the presence and absence of a lateral spread response, which provides critical information during microvascular decompression surgery for the treatment of hemifacial spasm using intraoperatively acquired electromyography images.

METHODS AND FINDINGS

A total of 3,674 image screenshots of monitoring devices from 50 patients were prepared, preprocessed, and then adopted into training and validation sets. A deep neural network was constructed using current-standard, off-the-shelf tools. The neural network correctly differentiated 50 test images (accuracy, 100%; area under the curve, 0.96) collected from 25 patients whose data were never exposed to the neural network during training or validation. The accuracy of the network was equivalent to that of the neuromonitoring technologists (p = 0.3013) and higher than that of neurosurgeons experienced in hemifacial spasm (p < 0.0001). Heatmaps obtained to highlight the key region of interest achieved a level similar to that of trained human professionals. Provisional clinical application showed that the neural network was preferable as an auxiliary tool.

CONCLUSIONS

A deep neural network trained on a dataset of intraoperatively collected electromyography data could classify the presence and absence of the lateral spread response with equivalent performance to human professionals. Well-designated applications based upon the neural network may provide useful auxiliary tools for surgical teams during operations.

Facial Nerve Massage for the Treatment of Hemifacial Spasm Refractory to Microvascular Decompression: Outcomes and Complications

BACKGROUND

After microvascular decompression (MVD) for hemifacial spasm (HFS), a minority of patients realize little to no relief of spasms. In some patients, the absence of relief of spasms results from incomplete or inadequate decompression of vascular compression of the facial nerve, and these patients represent excellent candidates for repeat MVD. However, in other patients, repeat MVD is not appropriate because adequate decompression and resolution of neurovascular compression, as determined by postoperative high-resolution MRI, was achieved with the initial operation.

OBJECTIVE

To present a cohort of patients with a history of HFS refractory to MVD, with no evidence of neurovascular compression on postoperative MRI, who underwent facial nerve massage (FNM) in the posterior fossa in an attempt to relieve spasms.

METHODS

Thirteen patients with a history of incomplete relief of spasms after technically adequate MVD surgery for hemifacial spasm underwent FNM. Immediate and long-term degree of spasm relief and complications after FNM were documented through in-person or telemedicine interview.

RESULTS

At follow-up after FNM, 7 of 12 patients (58.3%) reported complete spasm relief (grade I), 2 of 12 patients (16.7%) reported &gt;75% spasm relief (grade II), 0 patient (0%) reported &gt;50% spasm relief (grade III), 3 of 12 (25.0%) patients reported &lt;50% spasm relief (grade IV), and 1 patient was lost to follow-up. One patient experienced a delayed facial paresis, and another patient experienced high-frequency hearing loss.

CONCLUSION

After FNM, durable and, at least, partial relief of spasms with a relatively low complication rate was observed in most patients with HFS with incomplete relief of spasms after technically adequate prior MVD.

[Higher efficacy of botulinum toxin therapy for hemifacial spasm recurrence after vascular decompression. Case report and literature review]

Hemifacial spasm (HFS) is an involuntary synchronous tonic and/or clonic contraction of mimic muscles following ipsilateral facial nerve dysfunction. The last one is a result of neurovascular conflict between the facial nerve and vessel. Currently, vascular decompression is a pathogenetic treatment modality for primary HFS. Various authors describe postoperative recurrence of HFS, and botulinum toxin therapy remains the only option for these patients. We aimed to describe the efficacy of botulinum toxin therapy in patients with HFS recurrence after surgical vascular decompression. The article presents a female patient with a long-term history of HFS and botulinum toxin therapy (with different formulations). Efficacy of therapy gradually decreased (progressive reduction of intervals between injections). MRI revealed a close relationship between posterior inferior cerebellar artery and roots of acoustic-facial nerves near the brainstem. The patient underwent vascular decompression of the left facial nerve root under intraoperative monitoring with positive postoperative outcome. However, HFS symptoms recurred in 3 days after surgery. Botulinum toxin type A (BTA) injections were resumed with significant positive effect that can be explained by reduction of one of the factors involved into HFS. Thus, patients with HFS recurrence after vascular decompression may benefit from BTA therapy.

Factors Influencing Patient Satisfaction after Microvascular Decompression for Hemifacial Spasm: A Focus on Residual Spasms

INTRODUCTION

Patients with hemifacial spasm (HFS) experience improvement in symptoms after microvascular decompression (MVD); however, patient satisfaction is sometimes low. This study aimed to analyze the relationship between residual spasms and patient satisfaction, identify factors affecting satisfaction, and investigate the degree of improvement in spasms which result in patient satisfaction after surgery.

METHODS

297 patients who completed a questionnaire after MVD for HFS between March 2020 and June 2020 were included. Information on surgical outcomes and patient satisfaction was collected using the questionnaire, and their relationships were analyzed.

RESULTS

Among the 297 patients, the mean residual spasm percentage and patient satisfaction score were negatively correlated with 14.0% and 8.8 points, respectively. In addition to residual spasms, discomfort caused by persistent spasms, psychological problem-solving, better social life, and interpersonal relationship improvement were associated with satisfaction. There was no significant association between the presence of complications and satisfaction. There was no significant difference in the satisfaction score at up to 30% residual spasm, and the patients with 0-30% residual spasm had a satisfaction score of 7 points or higher.

CONCLUSION

Residual spasms and discomfort from residual spasms decreased patient satisfaction after MVD for HFS. It is then necessary to perform accurate surgical resolution to improve surgical outcomes and provide adequate management to reduce postoperative discomfort and anxiety, and ultimately to enhance satisfaction. Residual spasms of up to 30% compared with the preoperative severity can be considered a good outcome when evaluating surgical outcomes.

Prevalence and severity of neurovascular compression in hemifacial spasm patients

Hemifacial spasm is typically caused by vascular compression of the proximal intracranial facial nerve. Although the prevalence of neurovascular compression has been investigated in a cohort of patients with classical trigeminal neuralgia, the prevalence and severity of neurovascular compression has not been well characterized in patients with hemifacial spasm. We aimed to investigate whether presence and severity of neurovascular compression are correlated to the symptomatic side in patients with hemifacial spasm. All patients in our study were evaluated by a physician who specializes in the management of cranial nerve disorders. Once hemifacial spasm was diagnosed on physical exam, the patient underwent a dedicated cranial nerve protocol magnetic resonance imaging study on a 3 T scanner. Exams were retrospectively reviewed by a neuroradiologist blinded to the symptomatic side. The presence, severity, vessel type, and location of neurovascular compression along the facial nerve was recorded. Neurovascular compression was graded as contact alone (vessel touching the facial nerve) versus deformity (indentation or deviation of the nerve by the culprit vessel). A total of 330 patients with hemifacial spasm were included. The majority (232) were female while the minority (98) were male. The average age was 55.7 years. Neurovascular compression (arterial) was identified on both the symptomatic (97.88%) and asymptomatic sides (38.79%) frequently. Neurovascular compression from an artery along the susceptible/proximal portion of the nerve was much more common on the symptomatic side (96.36%) than on the asymptomatic side (12.73%), odds ratio = 93.00, P < 0.0001. When we assessed severity of arterial compression, the more severe form of neurovascular compression, deformity, was noted on the symptomatic side (70.3%) much more frequently than on the asymptomatic side (1.82%) (odds ratio = 114.00 P < 0.0001). We conclude that neurovascular compression that results in deformity of the susceptible portion of the facial nerve is highly associated with the symptomatic side in hemifacial spasm.

Quality of life after hemifacial spasm surgery: French versions of the HFS-8 and HFS-30 questionnaires

OBJECTIVES

The aim of the present study was to assess quality of life before and after surgery for hemifacial spasm, in order to validate two specific quality of life scales translated in French. Surgical results and complications were reported.

MATERIAL AND METHODS

Twenty-three patients with hemifacial spasm treated by microvascular decompression were retrospectively included. The HFS-8 and HFS-30 quality of life scales were translated from English into French using a forward-backward method and implemented on patients at least one year after surgery.

RESULTS

Median HFS-8 and HFS-30 values were respectively 16±12.5 (range: 8-20.5) and 38±38.5 (range: 23-61.5) before surgery and 0.5±4.5 (range: 0-4.5) and 5±17.5 (range: 1-18.5) after surgery, showing significant improvement in quality of life (P<0.001). The internal consistency of both scales was excellent (Cronbach's alpha>0.9), and they were significantly correlated (Pearson coefficient=0.95; 95% CI [0.91; 0.98]; P<0.0001). Success rates were 83% and 91%, respectively, after primary and revision surgeries. Complications were transient with minor consequences in 80% of cases, but could impact quality of life when lasting.

CONCLUSIONS

These results support the validity of the French versions of HFS-8 and HFS-30. Microvascular decompression is a safe and effective treatment for hemifacial spasm, and these scales are reliable tools to assess postoperative quality of life.

The Utility of Intraoperative Lateral Spread Recording in Microvascular Decompression for Hemifacial Spasm: A Systematic Review and Meta-Analysis

BACKGROUND

Microvascular decompression (MVD) is the surgical treatment of choice for hemifacial spasm (HFS). During MVD, monitoring of the abnormal lateral spread response (LSR), an evoked response to facial nerve stimulation, has been traditionally used to monitor adequacy of cranial nerve (CN) VII decompression.

OBJECTIVE

To assess the utility of LSR monitoring in predicting spasm-free status after MVD postoperatively.

METHODS

We searched PubMed, Web of Science, and Embase for relevant publications. We included studies reporting on intraoperative LSR monitoring during MVD for HFS and spasm-free status following the procedure. Sensitivity of LSR, specificity, diagnostic odds ratio, and positive predictive value were calculated.

RESULTS

From 148 studies, 26 studies with 7479 patients were ultimately included in this meta-analysis. The final intraoperative LSR status predicted the clinical outcome of MVD with the following specificities and sensitivities: 89% (0.83- 0.93) and 40% (0.30- 0.51) at discharge, 90% (0.84-0.94) and 41% (0.29-0.53) at 3 mo, 89% (0.83-0.93) and 40% (0.30-0.51) at 1 yr. When LSR persisted after MVD, the probability (95% CI) for HFS persistence was 47.8% (0.33-0.63) at discharge, 40.8% (0.23-0.61) at 3 mo, and 24.4% (0.13-0.41) at 1 yr. However, when LSR resolved, the probability for HFS persistence was 7.3% at discharge, 4.2% at 3 mo, and 4.0% at 1 yr.

CONCLUSION

Intraoperative LSR monitoring has high specificity but modest sensitivity in predicting the spasm-free status following MVD. Persistence of LSR carries high risk for immediate and long-term facial spasm persistence. Therefore, adequacy of decompression should be thoroughly investigated before closing in cases where intraoperative LSR persists.

The long-term effects of microvascular decompression on social phobia and health-related quality of life in patients with hemifacial spasm: a 3-year prospective study

BACKGROUND

Although not a life-threatening condition, hemifacial spasm (HFS) frequently leads to social phobia because it causes significant facial disfigurement and consequently reduces health-related quality of life (HRQoL). The purpose of the current study was to examine the long-term effects of MVD on psychological aspects and HRQoL in HFS patients with social anxiety over a 36-month follow-up.

METHODS

Thirty patients with HFS who underwent MVD from January 2015 to May 2015 were included in this prospective study. Clinical data, including standardized measures of general anxiety and depression (Hospital Anxiety Depression Scale (HADS)), social anxiety (Liebowitz Social Anxiety Scale (LSAS)), and the severity of HFS, were collected postoperatively, and 6 months and 36 months after MVD. Likewise, data on HRQoL were collected at baseline, and 6 months and 36 months after MVD using the Korean version of the Short Form 36 (SF-36).

RESULTS

Twenty-two patients who completed the 36-month follow-up were classified into social phobia group and non-social phobia group based on the LSAS total scores of 60. Repeated measures analysis of variance demonstrated significant differences between the two groups over time for the total LSAS score (p < 0.001), anxiety subscale score of the HADS (p = 0.002), and the Mental Component Summary (MCS) (p = 0.046) of the SF-36. A comparison of these two groups in terms of differences observed in their scales at 6 months after MVD has shown that the improvements of the social phobia group in HADS anxiety subscale (p = 0.010), LSAS total score (p = 0.008), and MCS (p = 0.040) were significantly more improved than the those of non-social phobia group. And at 36 months after surgery, the improvement of the scales mentioned above was maintained, and additionally Vitality (p = 0.040) and Mental Health (p = 0.040) dimensions showed a statistically significant improvement.

CONCLUSIONS

The improvements previously observed in psychological aspects and HRQoL over a short-term follow-up after MVD in HFS patients with social phobia were maintained for at least 36 months after MVD.

Geographic Disparities in the Surgical Management of Hemifacial Spasm in Canada

BACKGROUND

We aimed to interrogate the Canadian Institute for Health Information (CIHI) database in order to determine the geographic distribution and outcomes of microvascular decompression (MVD) for the treatment of hemifacial spasm (HFS).

METHODS

The CIHI database was searched from 2004 to 2017 for relevant diagnostic and procedure codes. A new database was populated with the following categories: year, institution, province, number of interventions per year, and mean length of stay. Descriptive statistics were generated. Provincial utilization rates of MVD for HFS were calculated.

RESULTS

During the period 2004-17, we identified 671 MVDs performed for HFS at 20 centers across Canada. During the study period, 286 MVDs (42.6%) were performed at one center in Manitoba. Another 131 (19.5%) and 72 (10.7%) were performed at one center in British Columbia and Ontario, respectively. The remaining 182 (27.1%) MVDs for HFS were performed at 17 centers across the rest of Canada where the mean number of cases performed per year was 1.1 (SD=0.9, range 0.2-2.9). When out-of-province cases were re-allocated to place of residence, the adjusted provincial utilization of MVD for HFS ranged between 0.5 and 6.1 patients per million per year.

CONCLUSIONS

Microvascular decompression for HFS is performed relatively rarely and there is a tremendous geographic variation in utilization across Canada. Although most of these surgeries are performed by a few surgeons, more than half of Canadian centers perform an average of less than 1 case per year. Further examination of the impact of these discrepancies appears warranted.

Toward Improving Safety in Neurosurgery with an Active Handheld Instrument

Microsurgical procedures, such as petroclival meningioma resection, require careful surgical actions in order to remove tumor tissue, while avoiding brain and vessel damaging. Such procedures are currently performed under microscope magnification. Robotic tools are emerging in order to filter surgeons' unintended movements and prevent tools from entering forbidden regions such as vascular structures. The present work investigates the use of a handheld robotic tool (Micron) to automate vessel avoidance in microsurgery. In particular, we focused on vessel segmentation, implementing a deep-learning-based segmentation strategy in microscopy images, and its integration with a feature-based passive 3D reconstruction algorithm to obtain accurate and robust vessel position. We then implemented a virtual-fixture-based strategy to control the handheld robotic tool and perform vessel avoidance. Clay vascular phantoms, lying on a background obtained from microscopy images recorded during petroclival meningioma surgery, were used for testing the segmentation and control algorithms. When testing the segmentation algorithm on 100 different phantom images, a median Dice similarity coefficient equal to 0.96 was achieved. A set of 25 Micron trials of 80 s in duration, each involving the interaction of Micron with a different vascular phantom, were recorded, with a safety distance equal to 2 mm, which was comparable to the median vessel diameter. Micron's tip entered the forbidden region 24% of the time when the control algorithm was active. However, the median penetration depth was 16.9 μm, which was two orders of magnitude lower than median vessel diameter. Results suggest the system can assist surgeons in performing safe vessel avoidance during neurosurgical procedures.