"Thursday 28 September"

Objective: Breathing-synchronised hypoglossal nerve stimulation is a treatment option for suitable patients with severe obstructive sleep apnea. The classical implantation technique requires three incisions: anterior submandibular to place the stimulating electrode on the hypoglossal nerve, subclavicular to place the impulse generator and on the lateral chest wall to place the sensor lead. More recently, a two incision technique has been propagated whereby the sensor lead is placed deeper to the IPG pocket. Our department switched to the 2-incision technique in May 2021 and we set out to compare the two methods in respect to the generated breath curves at implantation and clinical follow-up parameters.

Methods: Cases operated between October 2020 and September 2022 were included. Parameters considered included age, gender, BMI, OR time, positioning of the sensor lead, preoperative Apnea-Hypopnea Index (AHI) and Epsworth Sleepiness Scale (ESS). The generated breath curves were categorised by an independent expert blinded to the surgical technique into "good" and "satisfactory" curves regarding conduciveness to optimal stimulation.

Results: 24 patients were included. 5 of these were operated with the 3-incision technique. There were no significant differences in the recorded parameters among the two groups. The expert opinion on the breath curves did not vary between groups. Mean OR time was marginally shorter in the 2-incision group by 4% (138.2 minutes for the 2-incision vs. 144 minutes for the 3-incision group). This might however be attributed to increasing surgeon expertise over time.

Conclusion: The 2-incision technique generates breath curves at par with those generated with 3-incision implants. The limited patient data collected in this analysis suggests the OR-time can be reduced using the 2-incision technique. There were no cases of postoperative infection in our patient group but it can be postulated that a 2-incision implant might have a lower risk of infection due to the reduced wound surface.

The recent discovery that neurovascular compression of the vagus nerve can generate an intermittent tickling sensation in the lungs that triggers a chronic cough which can be cured with microvascular decompression (MVD) raises an important question.  What is the diagnostic test of choice?  There is a growing recognition of neurogenic cough by otolaryngologists and it is vitally important that neurosurgeons only operate on those with vagus associated neurogenic cough occurring due to unilateral encroachment of its root (VANCOUVER syndrome).  This study proposes two screening tests and the definitive diagnostic test of choice for VANCOUVER syndrome.

The vagus nerve provides sensation (tickle not pain) to the tracheobronchial tree. Similar to trigeminal neuralgia, intermittent sensations can be triggered by a vascular compression of the nerve (and cured with MVD). Continuing the analogy with trigeminal neuralgia, these vagus sensations – tickling that forces an irresistible cough - can be damped with anti-neuralgia medications and temporarily eliminated with local anesthetic. Our first screening test is inhaled nebulized lidocaine (a common procedure in the laryngologist’s office) which eliminates the tickling sensation and therefore coughing for the duration of the anesthetic effect. Our second screening test is MRI of the lower cranial nerves. A prospective analysis of 100 consecutive patients receiving MRI of their lower cranial nerves showed that half of asymptomatic individuals have a vessel compressing one their vagus nerves. Vascular compression of the vagus nerve is therefore required but not sufficient for the diagnosis.

Our proposed definitive diagnostic test is a unilateral percutaneous vagus nerve block. If coughing stops in response to a unilateral block and does not stop following a later contralateral block then the vagus pathology is unilateral. If that side correlates with a vascular compression of the vagus nerve on MRI, then consideration for MVD of that Xth nerve is offered.

The technique for vagus nerve block is presented with case examples. The intraoperative findings in VANCOUVER syndrome are presented.

Patients with hemi-laryngopharyngeal spasm (HeLPS syndrome) present with intermittent severe throat contractions and coughing due to neurovascular compression of the vagus nerve and can be cured with microvascular decompression (MVD) of the Xth nerve. Without treatment, symptoms can lead to tracheostomy and repeated syncope. Patients are often misdiagnosed as 'psychosomatic' because the condition is not recognized. A definitive diagnostic protocol is required because the symptoms of coughing and choking are common and compression of the vagus nerve can be seen in up to 50% of asymptomatic individuals’ MRI.

We propose a diagnostic protocol for hemi-laryngopharyngeal spasm. Patients are screened by a laryngologist to rule out common causes of throat contractions and cough. Laryngoscopy may demonstrate a pathognomonic unilateral vocal cord movement disorder in approximately one-third of patients (examples will be shown). Patients can lateralize their throat contractions if the affected muscles are in their pharynx (or if they have concomitant glossopharyngeal neuralgia). Patients will not be able to lateralize their symptoms and instead describe a circumferential choking if the affected muscles are in their larynx.  For patients who can not lateralize their symptoms, unilateral botulinum toxin injections into the affected laryngeal muscles will dramatically reduce the contractions for several months (similar to hemifacial spasm).  If contralateral injections, done at a later date (>3 months), do not relieve the muscle spasms then the vagus nerve pathology is unilateral.  If this correlates with the side of compression on an MRI, then consideration can be given to MVD of the Xth cranial nerve.

The intraoperative findings in hemi-laryngopharyngeal spasm are presented. Functional neurosurgeons need to be aware of this recently discovered medical condition and are encouraged to share this knowledge with their otolaryngology colleagues.

Objective. Interstitial photodynamic therapy (iPDT) is a minimally invasive treatment based on the interaction of light, a photosensitizer and oxygen. In brain gliomas, iPDT consists in the stereotaxic introduction of one or more light guides into the tumor area, without extensive craniotomy, to irradiate photosensitized tumor cells. iPDT causes necrosis and/or apoptosis of tumor cells, can destroy the tumor vasculature and induce an inflammatory reaction that triggers the stimulation of an antitumor immune response.

Purpose. To analyze the possibilities of iPDT in the treatment of deep-seated, small-sized relapses of malignant gliomas.

Materials and methods. The study with iPDT included 3 patients with a Karnofsky score of at least 70 points, who had a recurrence of single-focal limited malignant glioma after standard complex therapy. Local tumor recurrence, or tumor progression, did not exceed a maximum spread of 3 cm as determined by tumor enhancement on gadolinium T1-weighted MRI. Tumor tissue viability was preliminarily confirmed using minimally invasive stereotaxic biopsy procedures, followed by morphological examination to rule out effects associated with treatment or pseudoprogression of the tumor. The size limitation was based on the maximum number of light fibers per laser, since the optimal distance between light diffusers is about 7–9 mm, for accurate tissue irradiation without critical thermal effects. Photoditazine with the active ingredient chlorin e6 diluted in 200 ml of saline at the rate of 1 mg of the drug per 1 kg of the patient's body weight was used as a photosensitizer. Interstitial irradiation was performed using a laser (Latus 2.5 (Atkus, Russia)) with a wavelength of 662 nm and a maximum power of 2.5 W and cylindrical scattering fibers. Target volume was determined after combining multimodal CT images (contrast-enhanced scan, 0.6 mm axial slices) with preoperative MRI. Spatial accurate interstitial irradiation of the tumor volume was planned using software. The duration of irradiation did not exceed 15–20 min. To prevent the possibility of thermal tissue damage during irradiation, the bed was continuously irrigated with saline. The light dose averaged 150 J/cm2.

Results. Postoperative MRI performed within 24 hours after iPDT showed a decrease or absence of contrast enhancement in the PDT area, at a distance of about 10 mm from the irradiation center. No transient increase in edema around the tumor irradiation zone was observed. In 1 patient, a transient worsening of the neurological status was observed. Follow-up was followed in all 3 patients. The median duration of follow-up after iPDT was 13.9 months. The cause of death was tumor progression. Median overall survival from first diagnosis of malignant glioma to death was 25 months. Median time between first diagnosis and iPDT was 11 months.

Conclusions. Interstitial PDT of gliomas remains a challenging procedure due to the limited depth of light penetration into the brain tissue, the complex procedure for planning and implanting the irradiator, and the potential risk of clinical deterioration, especially after treatment in functionally significant areas of the brain. However, iPDT may be a promising treatment option in a high-risk patient population. It does not interfere with, but rather can complement, other treatment options for recurrent disease, such as repeat radiation therapy and chemotherapy. iPDT remains a potential option for deep-seated gliomas in patients with high surgical risk and tumor recurrence. The hospital stay can be 3-4 days, which reduces the cost of hospitalization. Patients treated with iPDT may receive adjuvant treatment faster than patients with standard craniotomy. These data strongly support further studies under controlled prospective conditions.

Introduction:

The craniopharyngioma, histologically benign tumor, is a disease of life.

Many authors agree to use the term remission rather than cure.

Microsurgical excision, radiosurgery and endocavitary treatments being different therapeutic choices which must be complementary.

Endocavitary treatment with interferon alpha 2b currently holds an important place in the therapeutic arsenal for craniopharyngioma cysts.

Methods :

Fourteen patients were treated with this even less invasive and structurally less aggressive technique of adjacent vessels and nerves.

Interferon alpha 2b is currently recognized as the least neurotoxic product among the various molecules to be instilled.

The placement of the subcutaneous reservoirs, Rickham or Omaya, is carried out under stereotactic conditions under MRI, assisted by neuronavigation allowing a better study of the trajectory and the structures with a path going from the entry orifice to our deep target.

Results :

Our series of cystic craniopharyngiomas treated with interferon alpha allowed us a satisfactory tumor control rate, comparable to the series published in the literature which are close to controls by nearly 80% with an interest in recurrent forms.

Conclusion:

This technique, practiced with a view to inhibiting the secretion of tumor fluid by the internal wall of the cyst, without significantly damaging the adjacent vascular and neural structures, is currently recognized and practiced for the treatment of this serious chronic pathology.

INTRODUCTION: The use of robot-assisted frameless stereotactic biopsy or laser ablation  is becoming more common. Among available robotic arms, Stealth Autoguide (Medtronic, Minneapolis, MN, USA) is a miniaturized device, that is used together with a standard head fixation device. Experience with the stealth autoguide is recent and limited to adult patients. The aim of this study is to present our preliminary  experience in pediatric patients.

METHODS: Clinical and surgical data of all patients undergoing frameless stereotactic biopsies using theStealth Autoguide from 2020 to May 2023 have been prospectively collected and retrospectively analyzed.

RESULTS: Thirty-four patients were included in the study; they underwent 15 bioptic procedures as stand-alone procedure and 19 laser ablation procedures . Mean age was 8 years old, range 2-18. The most common indication for biopsy was diffuse intrinsic brain stem tumor (to confirm diagnosis and to obtain tissue for molecular studies), followed by diffuse supratentorial tumor. Laser ablation was indicated for epilepsy (4 pts) , cavernoma (2 pts) or brain tumors (9 low grade tumors and 4 high grade tumors).  13 procedures were performed in prone position, 18 in supine position and 3 in lateral position. Facial surface registration was adopted in 5 cases. In all MRgLITT cases positioning of skull fixed fiducials were preferred and also , in the biopsy group, for patient in prone position and/or affected by deep lesion. In younger patients (less than 5 year-old), the head was fixed using a DORO skull clamp with 4 pediatric cranial pins, and it was also supported on the integrated Gel Head Ring, (DORO QR3 multipurpose skull clamp set - Pro Med Instruments). Diagnostic tissue samples were obtained in all cases and all patients received a definitive histological diagnosis. Laser fiber insertion was successuful in all MrgLITT patients. Neither mortality nor morbidity related to the surgical procedure were recorded.

CONCLUSION: The Stealth Autoguide was able to compensate for surgeon movement and , together with neuronavigation, provide real-time feedback during the procedure, leading to improved accuracy and reduced complications.  Our preliminary experience with the use of the Stealth Autoguide as an aid in frameless stereotactic procedures in pediatric neurosurgery suggests that this technology is safe, feasable and accurate also in pediatric patients. Virtually all position can be used, also prone position that is precluded to other kind of robotic arms.

Objective

Lesions of the posterior fossa (brainstem and cerebellum) are challenging regarding diagnosis and treatment since they are often located in eloquent areas and total resection is rarely possible. Therefore, frame-based stereotactic biopsies are commonly used to asservate tissue for neuropathological diagnosis and further treatment determination. The aim of our study was to assess the safety and diagnostic success rate of frame-based stereotactic biopsies for lesions in the posterior fossa via the suboccipital, transcerebellar approach.

Methods

We performed a retrospective database analysis of all frame-based stereotactic biopsy cases at our institution since 2007 to identify all cases of surgeries for infratentorial lesion biopsies via the suboccipital, transcerebellar approach. We collected clinical data regarding outcome, complications, diagnostic success, radiological appearances and stereotactic trajectories.

Results

A total of n=79 cases of stereotactic biopsies for posterior fossa lesions via the suboccipital, transcerebellar approach (41 women and 38 men) utilizing the Zamorano-Duchovny stereotactic system were identified. Mean age at the time of surgery was 42.5 years (+/-23.3, range: 1-87 years). All patients were operated with intraoperative stereotactic imaging (n=62 MRI, n=17 CT). The absolute diagnostic success rate was 87.3%. Most common diagnoses were glioma, lymphoma and inflammatory disease. The overall complication rate was 8.7% (7 cases). All patients with complications showed new neurological deficits which were permanent in 3 cases. Hemorrhage was detected in 5 cases with complications. The 30-day mortality rate was 7.6%, 1 year survival rate was 70.0%.

Conclusion

Our data suggests that frame-based stereotactic biospies with the Zamorano-Duchovny stereotactic system via the suboccipital, transcerebellar approach are safe and reliable for infratentorial lesions bearing a high diagnostic yield and an acceptable complication rate. Further research should focus on the planning of safe trajectories and a careful case selection with the goal to minimize complications and maximize diagnostic success.

Magnetic resonance imaging (MRI) is a powerful non-invasive technique that allows excellent contrast in soft tissues and high spatial resolution. Although MRI is the preferred imaging modality for stereotactic radiosurgery treatment planning, anatomic distortion is present in all MRI data due to hardware- and patient-related disturbances of the magnetic field homogeneity, thereby potentially jeopardizing the efficacy of SRS treatments. This study evaluated the potential for uncorrected MRI to lead to inadequate treatment planning in Gamma Knife radiosurgery (GKRS) for metastatic brain tumors (METs). We performed a retrospective analysis of 26 consecutive patients with 70 METs treated in our department from 2020-2021. MRIs were corrected for distortion using commercially available software (Cranial Distortion Correction, Brainlab Elements, Brainlab AG, Munich, Germany). To assess the clinical significance of anatomic distortion, an SRS plan was generated using each uncorrected tumor volume, and these plans were evaluated for coverage of the corrected tumor volume to demonstrate the dose distribution that would be achieved if the distortion had not been corrected. Plans were considered inadequate if ≥2% of the corrected tumor volume received less than 100% of the prescription dose. Displacement of the center of mass of the uncorrected tumor volume, relative to its corrected position, was measured for each lesion in millimeters. The median target volume was 0.381 cm³ (range, 0.01-12.382 cm³), and all radiosurgery plans met the optimization criterion of at least 98% of the uncorrected tumor volume (median 99.55%, range 98.1-100%) receiving at least 100% of the prescription dose. However, the percent of the corrected tumor volume receiving the full prescription dose was a median of 95.45%, with a range of 23.1-99.5%. The median displacement was 0.545 mm (range, 0.1-2.87 mm), and there was a statistically significant, strong negative correlation between corrected tumor volume and displacement (r=-.538, p<0.001). While MRI distortion is often subtle on visual inspection, this distortion has a significant clinical impact on SRS planning. Distortion-corrected MRI should uniformly be used for intracranial radiosurgery planning as distortion is sometimes sufficient to cause a volumetric miss of SRS targets. 

Objective: Medically refractory trigeminal neuralgia can be treated by microvascular decompression of the trigeminal nerve, by ablative percoutaneous treatments such as thermocoagulation, glycerol/ alcohol injection and ballon compression of the ganglion Gasseri or, far less invasive, by radiosurgery that has been proven to elegantly and highly effictively treat this pain condition. We here report about the results at our institution

Methods: We evaluated our outcomes retrospectively in our patients with medically refractory trigeminal neuralgia treated with radiosurgery. One 4mm shot was placed allong the  the trigeminal nerve (either retrogasserian, midcysternal or at the root entry zone) as the chosen target. Pain scores and side effects were documented regularely.

Results: 232 patients treated between the years 1999-2019 were included into this study. 15 patients received repeated gamma Knife radiosurgery. The average age was 65 years. 58 patients had prior therapies other than medication. Mean follow up was 406 days. Multiple sclerosis as a comorbidity was present in 38 patients. Pain condition last in average 10 years till radiosurgery was performed. The average dose was 89Gy.  The 10Gy volume oft he brain stem in average was 0,12ccm. Radiosurgery was succesfull in 78% as defined by the Barrow neurological institute pain score (BNI) I-III and failed in 22% oft he patients. Hypesthesia was seen in 12%. Pain quality changed to ongoing pain in 4 patients.

Conclusion: Radiosurgery is proven to be an effective and safe treatment option for trigeminal neuralgia and long term results are available. In our patients side effects are rare and less present then generally sited in the literature and its risk profile is lower compared to any other treatment. Given the fact of absent invasivness radiosurgery shoud be considered in the first place in patients with (high risk) comorbidities, elderly patients and patients with prior surgically treatments and refractory/ relapse pain condition. 

Introduction

MR-guided laser interstitial thermal therapy (MRgLITT) is a minimally invasive technique that can be used for treatment of deep-seated brain lesions. Currently the radiological changes that occur after the ablation are still not completely characterized.

The goal of this current study is to retrospectively examine the outcome and describe the radiological volume changes that occur after MRgLITT ablation of brain tumors.

Method

We retrospectively collected clinical and imaging data of all adults’ patients that underwent MRgLITT of brain tumors (primary and metastatic) between 2020-2023 at the Tel-Aviv Medical Center. Lesions’ volume, length and diameter were measured before, during and in follow-ups on T1-weighted images with contrast. The post-operative ablation volume was compared to Medtronic thermal damage estimate (TDE). Local control was assessed at last follow-up.

Results

Twenty patients (average age 57±11 years) were available for follow-up. Most lesions (n=11) were metastatic, and the rest 9 patients had high grade gliomas. Mean follow-up was 8±7.5 months. Average pre-op tumor volume was 2.26±1.96 CC³, and immediate post-op (in the end of the ablation) was 4.65±2.5 CC³. During follow-up the average lesion volume was: one week 7.7±4.85 CC³, 1-2 month 4.8±3.22 CC³, 3 months 4±3 CC³, 6 months 2±1.86 CC³ and 9 months 1.2±1.2 CC³. Forward extension of the enhancing lesion from the tip of the catheter post ablation was on average 3.4±2 mm. All high-grade glioma tumor had a failure (local/distance after 3-6 months).

Discussion

MRgLITT can cause an enlargement in the lesion volume during the first months after the ablation, moreover the forward thermal damage is around 4mm.

Title

Laser interstitial thermal therapy using an uncooled laser catheter in a diagnostic MR suite

Hjalmar Bjartmarz, Irena Grubor, Charlotte Edvardsson, Roger Siemund and Peter Siesjö
Skane University Hospital, Departments of Neurosurgery and Diagnostic Radiology, Skane University Hospital, Lund, Sweden,

Abstract

Background

Laser interstitial thermal therapy (LITT) has emerged as an alternative to open surgery for both primary and secondary brain tumors. Additionally, thermal ablation by laser can be used to eradicate epileptic foci and to treat radiation necrosis. During the procedure, a laser catheter has to be placed in the targeted lesion under navigation guidance. To control temperature during ablation MR thermography is utilized, thus the ablation procedure is commonly performed inside a dedicated intraoperative MR. As most catheter insertions are performed outside the MR camera, shorter or longer transports with the indwelling laser catheter are needed. This poses a potential hazard for unintentional catheter dislodgment during transport. Navigation procedures outside the MR camera can also result in misplacement of the catheter which can lead to abandonment of the procedure or return to the operative suite. Currently used catheters for thermal ablation necessitates a cooling procedure after ablation imposing additional risks and logistics. To minimize the above stated hazards, we here present a workflow where both catheter placement and ablation are performed inside a diagnostic MR suite using a new laser catheter without cooling.

Methods

In an open-label, pilot, exploratory, single centre, early feasibility and safety clinical phase 1-2 trial, patients with recurrent glioblastoma were included after informed consent. Patients 18-80 years with lesions < 30 mm were eligible. Single or multiple ablations were performed in a diagnostic MR suite using a MR compatible navigation system (ClearPoint® Neuro Navigation System) together with a new uncooled laser catheter and MR thermography (Tranberg Thermal Therapy System and Thermoguide Workstation).

Results

5 patients with recurrent glioblastoma fulfilling all inclusion criteria and no exclusion criteria were treated with single or multiple laser thermal ablations in a diagnostic MR suite.  Laser effects between 2 and 4 W were used with ablation times between 270 and 570 seconds. The workflow was executable and sustainable without any treatment related side effects or device mis performance noted. Details of the workflow will be presented.

Conclusions

LITT using a non-cooled laser catheter inside an outpatient MRI suite was feasible and reproducible. The procedure may reduce risks associated with LITT procedures.

Introduction
The standard frameless biopsy procedure is guided solely by preoperative images. Consequently, the procedure is associated with adverse events such as inconclusive results and hemorrhage. Intraoperative feedback relying on tissue fluorescence has been suggested [1]. Our group has previously presented an optical probe system [2] integrated into the biopsy needle. The system provides feedback on tissue characteristics in situ before the tissue sample is taken. However, further information could be gained through a multimodal approach. This study aimed to evaluate a pipeline that connects the in situ optical information to the pre-, intra-, and postoperative image information and neuropathological results for postoperative analysis.

Methods
Six patients planned for frameless needle biopsies were included in the study (written informed consent, EPM-2020-01404, mean age: 59, range: 18-78, two women). Inclusion was based on suspected malignant intracerebral tumors as identified by contrast enhancement on preoperative 3T MRI. An oral dose of Gliolan (20 mg/kg, Medac GmbH, Germany) was administered to the patient 2-3 h before anesthesia. Trajectory planning and frameless navigation were performed using the StealthStation® (S8, Medtronic Inc, USA). After burr-hole trephination and opening of the dura, the optical probe was placed in the modified outer cannula of the biopsy needle (Passive Biopsy Needle Kit, Medtronic Inc). Then, the probe-needle kit was secured in the AutoGuide® (Medtronic Inc). Errors between the preoperative images and the patient’s physical anatomy (i.e., registration) as well as between the locked and planned trajectory (i.e., targeting) were noted. Tissue fluorescence, perfusion, and gray-whiteness were measured in millimeter steps along the trajectory and displayed to the surgeon in real time. The corresponding coordinates on preoperative MRI were logged. When fluorescence peaks at 635 nm were registered at or in the vicinity of the precalculated target, the probe was replaced by the inner cannula of the biopsy needle, and tissue samples were taken. Postoperative images (CT or MRI) were acquired within 12 h of surgery on which final entry and biopsy positions were defined.

A pipeline for postoperative analysis of secondary outcomes and comparison of planned and actual trajectories was constructed. The pipeline combines pre-, intra-, and postoperative data and presents all data in preoperative navigation image space.

Results and Discussion
Real-time feedback on tissue fluorescence, perfusion, and light intensity was obtained in 70 locations. In six patients, tissue fluorescence was found (14 locations) and pathology results confirmed tissue samples to be tumorous after 30-60 minutes. In one patient, no fluorescence peak was detected; the tissue sample was confirmed to be non-tumor. For this patient, high perfusion signals were recorded before tissue sampling. Postoperative imaging confirmed a local (asymptomatic) hemorrhage. Final CNS WHO 2021 diagnoses included Glioblastoma IDH-wildtype, grade 4; Astrocytoma IDH-wildtype, high-grade; and Primary diffuse large B-cell lymphoma.

The registration and targeting errors were 1.3-2.1 mm and 0.1-0.5, respectively. The average shift between pre- and postoperative positions was 3.85 (±2.63) mm. This shift is believed to be a combination of errors during registration of the preoperative images to the patient’s physical anatomy, changed conditions (e.g., brain shift), and potential errors in the image coregistration process.

We present a pipeline combining pre-, intra-, and postoperative data. The pipeline allows postoperative analysis of secondary outcomes by combining optical signals, final biopsy positions, and neuropathology. This multimodal approach could give further insights into tumor location beyond navigation on preoperative MRI.

References
[1] Millesi, M.; Kiesel, B.; Wöhrer, A.; Mercea, P.A.; Bissolo, M.; Roetzer, T.; Wolfsberger, S.; Furtner, J.; Knosp, E.; Widhalm, G. Is Intraoperative Pathology Needed If 5-Aminolevulinic-Acid-Induced Tissue Fluorescence Is Found in Stereotactic Brain Tumor Biopsy? Neurosurgery 2020, 86, 366–373.
[2] Klint E, Mauritzon S, Ragnemalm B, Richter J, Wårdell K. FluoRa - a system for combined fluorescence and microcirculation measurements in brain tumor surgery. Annu Int Conf IEEE Eng Med Biol Soc. 2021;2021:1512-1515.

Background: Gamma Knife Radiosurgery (GKRS) has traditionally been considered the gold standard therapy for single-fraction high-dose irradiation of relatively small brain lesions. Despite the steep radiation dose gradient  used in the GK treatment, eloquent structures that lie within 2 to 5 mm from targets are considered at risk. Fractionated stereotactic radiosurgery (fSRS) delivered over 3 to 5 days, is used to treat tumors located next to critical structures such as the optic pathways in order to minimize healthy tissue toxicity.  In many centers an invasive Leksell pin-based frame system is still used with GKRS . It  represents an advantage in terms of accuracy and precision of the treatment, but it involves also a negative aspect in terms of treatment compliance.  The new generation of GKRS: “Leksell Gamma Knife Icon (GK Icon)”, utilizes a frameless immobilization system associated with cone-beam computed tomography (CBCT) to evaluate motion error. 

Objective: Analyze the feasibility of fractionated stereotactic radiosurgery with GK Icon system for the treatment of benign lesions in close proximity to the optical apparatus.  

Methods: Patients were treated with GK Icon system applying the combination of fGKRS and a frameless immobilization system. Clinical and radiological follow-up was performed and the incidence of side effects was compared to reported data about patients treated with fGKRS using a traditional frame to immobilize the patient’s head (qui va detto il punto forte del vostro studio). also Importantly, we studied the error in the daily repositioning of the patient in the X, Y, Z axes, for both rotation and translation in order to evaluate the accuracy of the repositioning.

Results: Radiological control was achieved in 99% of tumors. Most patients had stable clinical symptoms, while we observed improvement of initial symptoms in 3 patients (8,1%). Out of the 37 symptomatic patients at onset, 5 of them reported worsening symptoms (13,5%). None of asymptomatic patients become symptomatic. Overall the percentage of clinical worsening was 6%.

Conclusion:  fGKRS Icon combines accuracy, significantly steeper gradients, and lower total body dose of the GKRS with the flexibility of fractionated treatment combined with the frameless immobilization system.

Meningiomas located near a sinus or draining vein can cause  venous congestion and lead to the development of edema around the tumour. Stereotactic radiosurgery treatment may aggravate existing edema or induce delayed edema formation in a significant percentage of patients (5%- 10%). In this study, we developed a machine learning model to predict the occurrence of new edemas after Gamma Knife radiosurgery for meningiomas. Our model integrates radiomics features extracted from the pre- treatment MRI scans with clinical information and dosimetric data from the treatment plans. Data imbalance is taken into account with machine learning methods.  The model is explainable  globally and at single patient level with game theoretical Shapley values. Counterfactuals restricted to change only the dosimetric part are used to gain further insights on the predictions. 

Background: Neurosurgical stereotactic biopsies are afflicted by hemorrhage, neurological impairment, or inconclusive neuropathological results. Therefore, it is imperative to reach the tissue sampling site safely and precisely with minimum needle insertions. A system was designed for intraoperative feedback on the brain tissue and of 5-aminolevulinic acid (5-ALA) fluorescence and for blood vessel detection during stereotactic needle biopsies [1]. 

Methods: A probe with optical fibers was designed to fit into the outer cannula of a Sedan Side-Cutting Biopsy Kit 2 for the Leksell stereotactic system (Elekta, Sweden). An opening at the tip of the cannula allows emitting and receiving light while moving forward through untouched tissue by our in-house developed mechanical insertion device [2]. The probe simultaneously detects microvascular blood flow, gray-whiteness of the brain tissue, and 5-ALA fluorescence spectra along the trajectory. The probe is connected to the FluoRa system [3] for sampling, storage, and real-time display of the optical information in the OR.

Stereotactic biopsies were performed in three consecutive cases, males aged 45 to 68, with suspected malignant intracerebral tumors on MRI. Written consent was obtained. The patients were given 20 mg/kg 5-ALA (Gliolan^®, Medac, Germany) 3-4 hours preoperatively. The stereotactic frame was applied under anesthesia. A 3D-MRI (Ingenia 3T, Philips) including T1wGd-, T2w-, and FLAIR-sequences was acquired and registered in the stereotactic planning system (StealthStation S8, Medtronic, USA). Biopsy positions and trajectories were defined in each case. Through a burr hole trephination and a minimal dura mater incision, the biopsy needle with the optical probe inside was forwarded to the target points in millimeter steps while recording gray-whiteness (Total Light Intensity; TLI), microvascular blood flow (perfusion) and fluorescence (FL). The real-time measurements of the different modalities were displayed next to the stereotactic navigation system screen.

Results: The variations of the TLI matched the pathways through the brain tissue, from gray to white and darker in the tumor. No high perfusion was registered. The FL showed high peaks at 635 nm at the targets, confirming malignant tumor. The optical probe was then replaced by the inner cannula of the biopsy needle and tissue samples were taken from the spots of the highest fluorescence. The corresponding pathological findings were Glioblastoma in two cases and lymphoma in one case. 

Conclusions: Optical monitoring of the trajectory and identification of the target is safe and can reduce the number of needle insertions in stereotactic biopsies and shorten the procedure.

References:

[1] Richter J, Haj-Hosseini N, Milos P, Hallbeck M, Wårdell K. Optical brain biopsy with a fluorescence and vessel tracing probe. Oper Neurosurg. 2021;21(4):217-224. 

[2] Klint E, Mauritzon S, Ragnemalm B, Richter J, Wårdell K. FluoRa - a system for combined fluorescence and microcirculation measurements in brain tumor surgery. Annu Int Conf IEEE Eng Med Biol Soc. 2021;2021:1512-1515. 

[3] Wårdell K, Hemm-Ode S, Rejmstad P, Zsigmond P. High-resolution laser Doppler measurements of microcirculation in the deep brain structures: a method for potential vessel tracking. Stereotact Funct Neurosurg. 2016;94(1):1-9. 

INTRODUCTION

During awake surgery mapping of cognitive functions with the current standards,  inaccuracies, and redundant communication can occur by lack of clear testing methodology.

The neat definition and hence reproducibility of stimulation points, the asynchronous stimulation and task presentation, the kind of tasks where, are important criteria to obtain a precise and reliable cortical mapping.

Concerning subcortical mapping, there seems to develop a consensus about the need for continuous multimodal testing with time constraint and intermittent stimulation.

Avoidance of time gaps is essential.

METHODS

Cortical mapping should be analytical, with maximal specificity, while subcortical testing needs to be more ad hoc with maximally sensitive tasks. So we developed a module for both cortical and subcortical testing, adaptable to any team.

The cortical cognitive mapping module integrates in 1 screen (with all steps simultaneously available) :

1.           selection and presentation of tasks by neuro-psycho/linguist ,

2.           stimulation parameters,

3.           observation of patient’s face,

4.           visualisation of the stimulated cortex with overlay grid of stimulated points,

5.           evaluation of the results and its registration,

6.           recording of all the events (video)

For the subcortical testing, navigation data are integrated in the screen, coinciding with the resecting navigated CUSA-tip.

A dedicated multimodal task,  with simultaneous motor testing on touch screen for the patient,  is basically proposed.

In case of negative testing, CUSA-resection is performed within the checked area; the positive points are registered directly within the navigation.

As well for cortical as for subcortical mapping, stress is put on the sequencing of continuous  task presentation and stimulation (intermittent, synchronous with task,). When the bipolar stimulation is  provided by CUSA-tip and suction tip, time gaps are avoided.

RESULTS

A significant increase in accuracy and ergonomy is noted: in cortical mapping, the surgeon has to stimulate the indicated cortical preselected point, and the neuro-psycho/linguist evaluates with a simple mouse click – correct or not.

During subcortical testing, the accuracy of resection is enhanced since performed in a delimited stimulated area.

Since no time gaps occur,  an important gain of time is obtained; it is a closed loop system, with exclusion of communication errors.

The modules are versatile and adaptable to each team.

CONCLUSION

A module is proposed yielding an exhaustive corticosubcortical mapping, by which all relevant data are synthetised and integrated in one screen, intra- or postoperative re-evaluation is easy to obtain when the mapping is recorded, also valuable in redo-surgery and as future database.