Proposal for a magnetic resonance imaging protocol for the detection of epileptogenic lesions at early outpatient stages

SPECT-PET in Epilepsy and Clinical Approach in Evaluation

In epilepsy, a detailed history, blood chemistry, routine electroencephalography, and brain MRI are important for the diagnosis of seizure type or epilepsy syndrome for the decision of appropriate drug treatment. Although antiepileptic drugs are mostly successful for controlling epileptic seizures, 20%-30% patients are resistant to medical treatment and continue to have seizures. In this intractable patient group, surgical resection is the primarily preferred treatment option. This particular group of patients should be referred to the epilepsy center for detailed investigation and further treatment. When the results of electroencephalography, MRI, and clinical status are discordant or there is no structural lesion on MRI, ictal-periictal SPECT, and interictal PET play key roles for lateralization or localization of epileptic region and guidance for the subsequent subdural electrode placement in intractable epilepsy. SPECT and PET show the functional status of the brain. SPECT and PET play important roles in the evaluation of epilepsy sydromes in childhood by showing abnormal brain regions. Most of the experience has been gained with (18)FDG-PET, in this respect. (11)C-flumazenil-PET usually deliniates the seizure focus more smaller than (18)FDG-PET and is sensitive in identifying medial temporal sclerosis. (11)C-alpha-methyl-l-tryptophan is helpful in the differentiation of epileptogenic and nonepileptogenic regions in children especially in tuberous sclerosis and multifocal cortical dysplasia for the evaluation of surgery. Finally, when there is concordance among these detailed investigations, resective surgery or palliative procedures can be discussed individually.

Seven tesla MRI improves detection of focal cortical dysplasia in patients with refractory focal epilepsy

Objective

The aim of this study is to determine whether the use of 7 tesla (T) MRI in clinical practice leads to higher detection rates of focal cortical dysplasias in possible candidates for epilepsy surgery.

Methods

In our center patients are referred for 7 T MRI if lesional focal epilepsy is suspected, but no abnormalities are detected at one or more previous, sufficient‐quality lower‐field MRI scans, acquired with a dedicated epilepsy protocol, or when concealed pathology is suspected in combination with MR‐visible mesiotemporal sclerosis—dual pathology. We assessed 40 epilepsy patients who underwent 7 T MRI for presurgical evaluation and whose scans (both 7 T and lower field) were discussed during multidisciplinary epilepsy surgery meetings that included a dedicated epilepsy neuroradiologist. We compared the conclusions of the multidisciplinary visual assessments of 7 T and lower‐field MRI scans.

Results

In our series of 40 patients, multidisciplinary evaluation of 7 T MRI identified additional lesions not seen on lower‐field MRI in 9 patients (23%). These findings were guiding in surgical planning. So far, 6 patients underwent surgery, with histological confirmation of focal cortical dysplasia or mild malformation of cortical development.

Significance

Seven T MRI improves detection of subtle focal cortical dysplasia and mild malformations of cortical development in patients with intractable epilepsy and may therefore contribute to identification of surgical candidates and complete resection of the epileptogenic lesion, and thus to postoperative seizure freedom.

Introduction to Magnetic Resonance Imaging for Neurologists

PURPOSE OF REVIEW

In neuroradiology, highly sophisticated methods such as MRI are implemented to investigate different entities of the central nervous system and to acquire miscellaneous images where tissues display varying degrees of characteristic signal intensity or brightness. Compared to x-ray, CT, and ultrasound, MRI produces clearer images of tissues, body fluids, and fat. The basics of MRI may be unknown to neurologists; this article introduces MRI physics, techniques, and interpretation guidelines.

RECENT FINDINGS

This article discusses the basics of MRI to provide clinicians with the scientific underpinning of MRI technology and to help them better understand image features and improve their diagnosis and differential diagnosis by combining MRI characteristics with their knowledge of pathology and neurology.

SUMMARY

This article will help neurologists deepen their knowledge and understanding of MRI by introducing the basics of MRI physics, technology, image acquisition, protocols, and image interpretation.

Non-invasive Evaluation for Epilepsy Surgery

Epilepsy surgery is aimed to remove the brain tissues that are indispensable for generating patient's epileptic seizures. There are two purposes in the pre-operative evaluation: localization of the epileptogenic zone and localization of function. Surgery is planned to remove possible epileptogenic zone while preserving functional area. Since no single diagnostic modality is superior to others in identifying and localizing the epileptogenic zone, multiple non-invasive evaluations are performed to estimate the location of the epileptogenic zone after concordance between evaluations. Essential components of non-invasive pre-surgical evaluation of epilepsy include detailed clinical history, long-term video-electroencephalography monitoring, epilepsy-protocol magnetic resonance imaging (MRI), and neuropsychological testing. However, a significant portion of drug-resistant epilepsy is associated with no or subtle MRI lesions or with ambiguous electro-clinical signs. Additional evaluations including fluoro-deoxy glucose positron emission tomography (FDG-PET), magnetoencephalography and ictal single photon emission computed tomography can play critical roles in planning surgery. FDG-PET should be registered on three-dimensional MRI for better detection of focal cortical dysplasia. All diagnostic tools are complementary to each other in defining the epileptogenic zone, so that it is always important to reassess the data based on other results to pick up or confirm subtle abnormalities.

MRI in the evaluation of localization-related epilepsy

This article covers the MRI evaluation of patients with epilepsy, with a focus on neuroimaging in those with localization-related epilepsy who may be potential epilepsy surgery candidates. The article includes structural MRI to identify a lesion, functional MRI to identify the eloquent cortex and diffusion tensor imaging to identify the eloquent white matter tracts. We consider the equipment, protocol or procedures, and reporting of MRI in patients with epilepsy. Recommendations for both adult and pediatric patients are described for protocols and procedures. The authors hope that this article will provide a standardized approach for clinical imaging of patients with suspected localization-related epilepsy who may be evaluated for epilepsy surgery. J. Magn. Reson. Imaging 2016.

Current use of imaging and electromagnetic source localization procedures in epilepsy surgery centers across Europe

OBJECTIVE

In 2014 the European Union-funded E-PILEPSY project was launched to improve awareness of, and accessibility to, epilepsy surgery across Europe. We aimed to investigate the current use of neuroimaging, electromagnetic source localization, and imaging postprocessing procedures in participating centers.

METHODS

A survey on the clinical use of imaging, electromagnetic source localization, and postprocessing methods in epilepsy surgery candidates was distributed among the 25 centers of the consortium. A descriptive analysis was performed, and results were compared to existing guidelines and recommendations.

RESULTS

Response rate was 96%. Standard epilepsy magnetic resonance imaging (MRI) protocols are acquired at 3 Tesla by 15 centers and at 1.5 Tesla by 9 centers. Three centers perform 3T MRI only if indicated. Twenty-six different MRI sequences were reported. Six centers follow all guideline-recommended MRI sequences with the proposed slice orientation and slice thickness or voxel size. Additional sequences are used by 22 centers. MRI postprocessing methods are used in 16 centers. Interictal positron emission tomography (PET) is available in 22 centers; all using 18F-fluorodeoxyglucose (FDG). Seventeen centers perform PET postprocessing. Single-photon emission computed tomography (SPECT) is used by 19 centers, of which 15 perform postprocessing. Four centers perform neither PET nor SPECT in children. Seven centers apply magnetoencephalography (MEG) source localization, and nine apply electroencephalography (EEG) source localization. Fourteen combinations of inverse methods and volume conduction models are used.

SIGNIFICANCE

We report a large variation in the presurgical diagnostic workup among epilepsy surgery centers across Europe. This diversity underscores the need for high-quality systematic reviews, evidence-based recommendations, and harmonization of available diagnostic presurgical methods.

Brain imaging in the assessment for epilepsy surgery

Brain imaging has a crucial role in the presurgical assessment of patients with epilepsy. Structural imaging reveals most cerebral lesions underlying focal epilepsy. Advances in MRI acquisitions including diffusion-weighted imaging, post-acquisition image processing techniques, and quantification of imaging data are increasing the accuracy of lesion detection. Functional MRI can be used to identify areas of the cortex that are essential for language, motor function, and memory, and tractography can reveal white matter tracts that are vital for these functions, thus reducing the risk of epilepsy surgery causing new morbidities. PET, SPECT, simultaneous EEG and functional MRI, and electrical and magnetic source imaging can be used to infer the localisation of epileptic foci and assist in the design of intracranial EEG recording strategies. Progress in semi-automated methods to register imaging data into a common space is enabling the creation of multimodal three-dimensional patient-specific datasets. These techniques show promise for the demonstration of the complex relations between normal and abnormal structural and functional data and could be used to direct precise intracranial navigation and surgery for individual patients.

Computational analysis in epilepsy neuroimaging: A survey of features and methods

Epilepsy affects 65 million people worldwide, a third of whom have seizures that are resistant to anti-epileptic medications. Some of these patients may be amenable to surgical therapy or treatment with implantable devices, but this usually requires delineation of discrete structural or functional lesion(s), which is challenging in a large percentage of these patients.

Advances in neuroimaging and machine learning allow semi-automated detection of malformations of cortical development (MCDs), a common cause of drug resistant epilepsy. A frequently asked question in the field is what techniques currently exist to assist radiologists in identifying these lesions, especially subtle forms of MCDs such as focal cortical dysplasia (FCD) Type I and low grade glial tumors. Below we introduce some of the common lesions encountered in patients with epilepsy and the common imaging findings that radiologists look for in these patients. We then review and discuss the computational techniques introduced over the past 10 years for quantifying and automatically detecting these imaging findings. Due to large variations in the accuracy and implementation of these studies, specific techniques are traditionally used at individual centers, often guided by local expertise, as well as selection bias introduced by the varying prevalence of specific patient populations in different epilepsy centers. We discuss the need for a multi-institutional study that combines features from different imaging modalities as well as computational techniques to definitively assess the utility of specific automated approaches to epilepsy imaging. We conclude that sharing and comparing these different computational techniques through a common data platform provides an opportunity to rigorously test and compare the accuracy of these tools across different patient populations and geographical locations. We propose that these kinds of tools, quantitative imaging analysis methods and open data platforms for aggregating and sharing data and algorithms, can play a vital role in reducing the cost of care, the risks of invasive treatments, and improve overall outcomes for patients with epilepsy.

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We introduce common epileptogenic lesions encountered in patients with drug resistant epilepsy.

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We discuss state of the art computational techniques used to detect lesions.

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There is a need for multi-institutional studies that combine these techniques.

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Clinically validated pipelines alongside the advances in imaging and electrophysiology will improve outcomes.

International Veterinary Epilepsy Task Force recommendations for a veterinary epilepsy-specific MRI protocol

Epilepsy is one of the most common chronic neurological diseases in veterinary practice. Magnetic resonance imaging (MRI) is regarded as an important diagnostic test to reach the diagnosis of idiopathic epilepsy. However, given that the diagnosis requires the exclusion of other differentials for seizures, the parameters for MRI examination should allow the detection of subtle lesions which may not be obvious with existing techniques. In addition, there are several differentials for idiopathic epilepsy in humans, for example some focal cortical dysplasias, which may only apparent with special sequences, imaging planes and/or particular techniques used in performing the MRI scan. As a result, there is a need to standardize MRI examination in veterinary patients with techniques that reliably diagnose subtle lesions, identify post-seizure changes, and which will allow for future identification of underlying causes of seizures not yet apparent in the veterinary literature.

There is a need for a standardized veterinary epilepsy-specific MRI protocol which will facilitate more detailed examination of areas susceptible to generating and perpetuating seizures, is cost efficient, simple to perform and can be adapted for both low and high field scanners. Standardisation of imaging will improve clinical communication and uniformity of case definition between research studies. A 6–7 sequence epilepsy-specific MRI protocol for veterinary patients is proposed and further advanced MR and functional imaging is reviewed.

Supratentorial white matter blurring associated with voltage-gated potassium channel-complex limbic encephalitis

INTRODUCTION

Limbic encephalitis (LE) associated with voltage-gated potassium channel-complex antibodies (VGKC-LE) is frequently non-paraneoplastic and associated with marked improvement following corticosteroid therapy. Mesial temporal lobe abnormalities are present in around 80 % of patients. If associated or preceded by faciobrachial dystonic seizures, basal ganglia signal changes may occur. In some patients, blurring of the supratentorial white matter on T2-weighted images (SWMB) may be seen. The purpose of this study was to evaluate the incidence of SWMB and whether it is specific for VGKC-LE.

METHODS

Two experienced neuroradiologists independently evaluated signal abnormalities on FLAIR MRI in 79 patients with LE while unaware on the antibody type.

RESULTS

SWMB was independently assessed as present in 10 of 36 (28 %) compared to 2 (5 %) of 43 non-VGKC patients (p = 0.009). It was not related to the presence of LGI1 or CASPR2 proteins of VGKC antibodies. MRI showed increased temporomesial FLAIR signal in 22 (61 %) VGKC compared to 14 (33 %) non-VGKC patients (p = 0.013), and extratemporomesial structures were affected in one VGKC (3 %) compared to 11 (26 %) non-VGKC patients (p = 0.005).

CONCLUSION

SWMB is a newly described MRI sign rather specific for VGKC-LE.

Look back to leap forward: The emerging new role of magnetoencephalography (MEG) in nonlesional epilepsy

This review considers accumulating evidence for a new role of MEG/MSI in increasing the diagnostic yield of supposedly negative MRIs, and suggests changes in the use of MEG/MSI in presurgical epilepsy evaluations. Specific alterations in practice protocols for both the MEG practitioner (i.e. physician magnetoencephalographer) and MEG user (i.e. referring physician) are proposed that should further enhance the overall value of MEG/MSI. Although advances in MEG analysis methods will likely become increasingly assisted by computers, interpretive competency and prudent clinical judgment remain irreplaceable.

Presurgical MR Imaging in Epilepsy

Primary goal of magnetic resonance imaging in epilepsy patients is to detect epileptogenic lesions with small lesions best detectable on a 3D FLAIR SPACE sequence with 1 mm(3) voxels. Morphometric analysis of 3D T1-weighted data sets helps to find subtle lesions and may reveal the true extent of a lesion. In further presurgical work-up, language lateralization and spatial relationship of epileptogenic lesions to eloquent cortex and white matter tracts must be evaluated. With clear left lateralization language, fMRI is sufficient; in atypical lateralizations, Wada test and electrical stimulation mapping may be added. Primary motor cortex and corticospinal tract on one and visual cortex and optic radiation on the other side are displayed with fMRI and diffusion tensor tractography. For the corticospinal tract a "global" tracking algorithm, for the optic radiation including Meyer' loop, which may be damaged in anterior temporal lobe resections, a probabilistic algorithm is best suited.

Magnetic resonance imaging in adults with epilepsy: a pictorial essay

This pictorial essay highlights the role of the radiologist as a member of the adult epilepsy multidisciplinary team, and gives an overview of MRI-evident epileptogenic lesions.