Comparing radiation dose of image-guided techniques in lumbar fusion surgery with pedicle screw insertion; A systematic review

Background Context

Fluoroscopic devices can be used to visualize subcutaneous and osseous tissue, a useful feature during pedicle screw insertion in lumbar fusion surgery. It is important that both patient and surgeon are exposed as little as possible, since these devices use potential harmful ionizing radiation.

Purpose

This study aims to compare radiation exposure of different image-guided techniques in lumbar fusion surgery with pedicle screw insertion.

Study Design

Systematic review.

Methods

Cochrane, Embase, PubMed and Web of Science databases were used to acquire relevant studies. Eligibility criteria were lumbar and/or sacral spine, pedicle screw, mGray and/or Sievert and/or mrem, radiation dose and/or radiation exposure. Image-guided techniques were divided in five groups: conventional C-arm, C-arm navigation, C-arm robotic, O-arm navigation and O-arm robotic. Comparisons were made based on effective dose for patients and surgeons, absorbed dose for patients and surgeons and exposure. Risk of bias was assessed using the 2017 Cochrane Risk of Bias tool on RCTs and the Cochrane ROBINS-I tool on NRCTs. Level of evidence was assessed using the guidelines of Oxford Centre for Evidence-based Medicine 2011.

Results

A total of 1423 studies were identified of which 38 were included in the analysis and assigned to one of the five groups. Results of radiation dose per procedure and per pedicle screw were described in dose ranges. Conventional C-arm appeared to result in higher effective dose for surgeons, higher absorbed dose for patients and higher exposure, compared to C-arm navigation/robotic and O-arm navigation/robotic. Level of evidence was 3 to 4 in 29 studies. Risk of bias of RCTs was intermediate, mostly due to inadequate blinding. Overall risk of bias score in NRCTs was determined as 'serious'.

Conclusions

Ranges of radiation doses using different modalities during pedicle screw insertion in lumbar fusion surgery are wide. Based on the highest numbers in the ranges, conventional C-arm tends to lead to a higher effective dose for surgeons, higher absorbed dose for patients and higher exposure, compared to C-arm-, and O-arm navigation/robotic. The level of evidence is low and risk of bias is fairly high. In future studies, heterogeneity should be limited by standardizing measurement methods and thoroughly describing the image-guided technique settings.

Value of ultra-high field MRI in patients with suspected focal epilepsy and negative 3 T MRI (EpiUltraStudy): protocol for a prospective, longitudinal therapeutic study

PURPOSE

Resective epilepsy surgery is a well-established, evidence-based treatment option in patients with drug-resistant focal epilepsy. A major predictive factor of good surgical outcome is visualization and delineation of a potential epileptogenic lesion by MRI. However, frequently, these lesions are subtle and may escape detection by conventional MRI (≤ 3 T).

METHODS

We present the EpiUltraStudy protocol to address the hypothesis that application of ultra-high field (UHF) MRI increases the rate of detection of structural lesions and functional brain aberrances in patients with drug-resistant focal epilepsy who are candidates for resective epilepsy surgery. Additionally, therapeutic gain will be addressed, testing whether increased lesion detection and tailored resections result in higher rates of seizure freedom 1 year after epilepsy surgery. Sixty patients enroll the study according to the following inclusion criteria: aged ≥ 12 years, diagnosed with drug-resistant focal epilepsy with a suspected epileptogenic focus, negative conventional 3 T MRI during pre-surgical work-up.

RESULTS

All patients will be evaluated by 7 T MRI; ten patients will undergo an additional 9.4 T MRI exam. Images will be evaluated independently by two neuroradiologists and a neurologist or neurosurgeon. Clinical and UHF MRI will be discussed in the multidisciplinary epilepsy surgery conference. Demographic and epilepsy characteristics, along with postoperative seizure outcome and histopathological evaluation, will be recorded.

CONCLUSION

This protocol was reviewed and approved by the local Institutional Review Board and complies with the Declaration of Helsinki and principles of Good Clinical Practice. Results will be submitted to international peer-reviewed journals and presented at international conferences.

TRIAL REGISTRATION NUMBER

www.trialregister.nl : NTR7536.

Ultra-high field magnetic resonance imaging in human epilepsy: A systematic review

RATIONALE

Resective epilepsy surgery is an evidence-based curative treatment option for patients with drug-resistant focal epilepsy. The major preoperative predictor of a good surgical outcome is detection of an epileptogenic lesion by magnetic resonance imaging (MRI). Application of ultra-high field (UHF) MRI, i.e. field strengths ≥ 7 Tesla (T), may increase the sensitivity to detect such a lesion.

METHODS

A keyword search strategy was submitted to Pubmed, EMBASE, Cochrane Database and clinicaltrials.gov to select studies on UHF MRI in patients with epilepsy. Follow-up study selection and data extraction were performed following PRISMA guidelines. We focused on I) diagnostic gain of UHF- over conventional MRI, II) concordance of MRI-detected lesion, seizure onset zone and surgical decision-making, and III) postoperative histopathological diagnosis and seizure outcome.

RESULTS

Sixteen observational cohort studies, all using 7T MRI were included. Diagnostic gain of 7T over conventional MRI ranged from 8% to 67%, with a pooled gain of 31%. Novel techniques to visualize pathological processes in epilepsy and lesion detection are discussed. Seizure freedom was achieved in 73% of operated patients; no seizure outcome comparison was made between 7T MRI positive, 7T negative and 3T positive patients. 7T could influence surgical decision-making, with high concordance of lesion and seizure onset zone. Focal cortical dysplasia (54%), hippocampal sclerosis (12%) and gliosis (8.1%) were the most frequently diagnosed histopathological entities.

SIGNIFICANCE

UHF MRI increases, yet variably, the sensitivity to detect an epileptogenic lesion, showing potential for use in clinical practice. It remains to be established whether this results in improved seizure outcome after surgical treatment. Prospective studies with larger cohorts of epilepsy patients, uniform scan and sequence protocols, and innovative post-processing technology are equally important as further increasing field strengths. Besides technical ameliorations, improved correlation of imaging features with clinical semiology, histopathology and clinical outcome has to be established.

Protocol for intraoperative assessment of the human cerebrovascular glycocalyx

INTRODUCTION

Adequate functioning of the blood-brain barrier (BBB) is important for brain homoeostasis and normal neuronal function. Disruption of the BBB has been described in several neurological diseases. Recent reports suggest that an increased permeability of the BBB also contributes to increased seizure susceptibility in patients with epilepsy. The endothelial glycocalyx is coating the luminal side of the endothelium and can be considered as the first barrier of the BBB. We hypothesise that an altered glycocalyx thickness plays a role in the aetiology of temporal lobe epilepsy (TLE), the most common type of epilepsy. Here, we propose a protocol that allows intraoperative assessment of the cerebrovascular glycocalyx thickness in patients with TLE and assess whether its thickness is decreased in patients with TLE when compared with controls.

METHODS AND ANALYSIS

This protocol is designed as a prospective observational case-control study in patients who undergo resective brain surgery as treatment for TLE. Control subjects are patients without a history of epileptic seizures, who undergo a craniotomy or burr hole surgery for other indications. Intraoperative glycocalyx thickness measurements of sublingual, cortical and hippocampal microcirculation are performed by video microscopy using sidestream dark-field imaging. Demographic details, seizure characteristics, epilepsy risk factors, intraoperative haemodynamic parameters and histopathological evaluation are additionally recorded.

ETHICS AND DISSEMINATION

This protocol has been ethically approved by the local medical ethical committee (ID: NL51594.068.14) and complies with the Declaration of Helsinki and principles of Good Clinical Practice. Informed consent is obtained before study enrolment and only coded data will be stored in a secured database, enabling an audit trail. Results will be submitted to international peer-reviewed journals and presented at international conferences.

TRIAL REGISTRATION NUMBER

NTR5568.

Morphology of the human cervical vagus nerve: implications for vagus nerve stimulation treatment

OBJECTIVES

The vagus nerve has gained a role in the treatment of certain diseases by the use of vagus nerve stimulation (VNS). This study provides detailed morphological information regarding the human cervical vagus nerve at the level of electrode implant.

RESULTS

Eleven pairs of cervical vagus nerves and four pairs of intracranial vagus nerves were analysed by the use of computer software. It was found that the right cervical vagus nerve has an 1.5 times larger effective surface area on average than the left nerve [1,089,492 ± 98,337 vs 753,915 ± 102,490 μm(2), respectively, (P < 0.05)] and that there is broad spreading within the individual nerves. At the right side, the mean effective surface area at the cervical level (1,089,492 ± 98,337 μm(2)) is larger than at the level inside the skull base (630,921 ± 105,422) (P < 0.05). This could imply that the vagus nerve receives anastomosing and 'hitchhiking' branches from areas other than the brainstem. Furthermore, abundant tyrosine hydroxylase (TH)- and dopamine ß-hydroxylase (DBH)-positive staining nerve fibres could be identified, indicating catecholaminergic neurotransmission. In two of the 22 cervical nerves, ganglion cells were found that also stained positive for TH and DBH. Stimulating the vagus nerve may therefore induce the release of dopamine and noradrenaline. A sympathetic activation could therefore be part of mechanism of action of VNS. Furthermore, it was shown that the right cervical vagus nerve contains on average two times more TH-positive nerve fibres than the left nerve (P < 0.05), a fact that could be of interest upon choosing stimulation side. We also suggest that the amount of epineurial tissue could be an important variable for determining individual effectiveness of VNS, because the absolute amount of epineurial tissue is widely spread between the individual nerves (ranging from 2,090,000 to 11,683,000 μm(2)).

CONCLUSIONS

We conclude by stating that one has to look at the vagus nerve as a morphological entity of the peripheral autonomic nervous system, a composite of different fibres and (anastomosing and hitchhiking) branches of different origin with different neurotransmitters, which can act both parasympathetic and sympathetic. Electrically stimulating the vagus nerve therefore is not the same as elevating the 'physiological parasympathetic tone', but may also implement catecholaminergic (sympathetic) effects.

Tonic GABAA Receptors as Potential Target for the Treatment of Temporal Lobe Epilepsy

Tonic GABA_A receptors are a subpopulation of receptors that generate long-lasting inhibition and thereby control network excitability. In recent years, these receptors have been implicated in various neurological and psychiatric disorders, including Parkinson’s disease, schizophrenia, and epilepsy. Their distinct subunit composition and function, compared to phasic GABA_A receptors, opens the possibility to specifically modulate network properties. In this review, the role of tonic GABA_A receptors in epilepsy and as potential antiepileptic target will be discussed.

The effects of vagus nerve stimulation on tryptophan metabolites in children with intractable epilepsy

BACKGROUND

The mechanism of action of vagus nerve stimulation (VNS) in intractable epilepsy is not entirely clarified. It is believed that VNS causes alterations in cytokines, which can lead to rebalancing the release of neurotoxic and neuroprotective tryptophan metabolites. We aimed to evaluate VNS effects on tryptophan metabolites and on epileptic seizures and investigated whether the antiepileptic effectiveness correlated with changes in tryptophan metabolism.

METHODS

Forty-one children with intractable epilepsy were included in a randomized, active-controlled, double-blind study. After a baseline period of 12 weeks, all children underwent implantation of a vagus nerve stimulator and entered a blinded active-controlled phase of 20 weeks. Half of the children received high-output (therapeutic) stimulation (n=21), while the other half received low-output (active control) stimulation (n=20). Subsequently, all children received high-output stimulation for another 19 weeks (add-on phase). Tryptophan metabolites were assessed in plasma and cerebrospinal fluid (CSF) by use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and compared between high- and low-output groups and between the end of both study phases and baseline. Seizure frequency was recorded using seizure diaries. Mood was assessed using Profile of Mood States (POMS) questionnaires.

RESULTS

Regarding tryptophan metabolites, anthranilic acid (AA) levels were significantly higher at the end of the add-on phase compared with baseline (p=0.002) and correlated significantly with improvement of mood (τ=-0.39, p=0.037) and seizure frequency reduction (τ=-0.33, p<0.01). No significant changes were found between high- and low-output groups regarding seizure frequency.

CONCLUSION

Vagus nerve stimulation induces a consistent increase in AA, a neuroprotective and anticonvulsant tryptophan metabolite. Moreover, increased AA levels are associated with improvement in mood and reduction of seizure frequency.

Vagus nerve stimulation in refractory epilepsy: effects on pro- and anti-inflammatory cytokines in peripheral blood

OBJECTIVE

The vagus nerve has important immunological functions that may be relevant for its anticonvulsive action. We postulate that this anticonvulsive action is activated by a shift in the immune system resulting in a reduction of neurotoxic and an increase of neuroprotective tryptophan metabolites.

METHODS

Eleven patients with refractory epilepsy and 11 controls matched for age and gender were included in this study. The primary outcome measure was a 50% seizure reduction. Other variables were pro-inflammatory cytokines IL-6 and TNF-α, anti-inflammatory cytokine IL-10, cortisol, and the tryptophan metabolites 3-hydroxykynurenine (3-OH-KYN), kynurenic acid (KYNA), kynurenine, serotonin (5-HT) and 5-hydroxyindol acetic acid (5-HIAA). Blood samples were scheduled during baseline, and in week 28 of add-on treatment.

RESULTS

IL-6 levels were higher in the responders than in the control group, and decreased after vagus nerve stimulation (VNS), whereas IL-10 was low and increased after VNS. In nonresponders, VNS resulted in an increase of IL-6 plasma levels and in a decrease of IL-10. Cortisol concentrations are higher in the epilepsy group than in the control group. After VNS, these concentrations decreased. The concentrations of the tryptophan metabolites were lower in the epilepsy group than in the control group. The KYNA ratios are defined as the ratio of neuroprotective KYNA versus neurotoxic 3-OH-KYN and KYNA versus neurotoxic kynurenine: these ratios were lower in epilepsy patients than in controls, and they both moderately increased after VNS.

CONCLUSION

The outcome of this preliminary study indicates that VNS causes a rebalancing of the immune system. This results in: (1) a reduction of neurotoxic and an increase of neuroprotective kynurenine metabolites and (2) in the normalization of cortisol levels.