Positron Emission Tomography In Epilepsy Research Articles

The Utility of Positron Emission Tomography in Epilepsy.

The role of fludeoxyglucose F 18 positron emission tomography (PET) in the presurgical evaluation of patients with medically intractable epilepsy continues to be refined. The purpose of this study was to systematically review the literature to assess the diagnostic accuracy and utility of PET in this setting. Thirty-nine studies were identified through MEDLINE and EMBASE databases that met the inclusion criteria. In adult patients, PET hypometabolism showed a 56 to 90% agreement with seizure onset localized by intracranial electroencephalogram (pediatric: 21 to 86%). In temporal lobe epilepsy patients with good surgical outcome, PET displayed moderate to high sensitivity in localizing the seizure focus (range: 71 to 89%). The sensitivity increased by 8 to 23% when PET results were combined with magnetic resonance imaging or electroencephalogram. PET has been shown to affect patient management by improving the guidance of intracranial electrodes placement, altering the decision to perform surgery, or excluding patients from further evaluation.

PET and SPECT in epilepsy

Epilepsy is one of the most frequent chronic neurological disorders, affecting 1–2% of the population. Patients with complex partial drug resistant episodes may benefit from a surgical treatment consisting in the excision of the epileptogenic area. Localization of the epileptogenic area was classically performed with video-EEG and magnetic resonance (MR). Recently, functional neuroimaging studies of nuclear medicine, positron emission tomography (PET) and single photon emission tomography (SPECT) have demonstrated their utility in the localization of the epileptogenic area prior to surgery. Ictal SPECT with brain perfusion tracers show an increase in blood flow in the initial ictal focus, while PET with 18FDG demonstrates a decrease of glucose metabolism in the interictal functional deficit zone.In this review, the basic principles and methodological characteristics of the SPECT and PET in epilepsy are described. The ictal SPECT injection mechanism, different patterns of perfusion based on the time of ictal, postictal or interictal injection are detailed and the different diagnostic sensitivities of each one of these SPECT are reviewed. Different methods of analysis of the images by subtraction and fusion systems with the MR are described. Similarly, the injection methodology, quantification and evaluation of the images of the PET in epilepsy are described. Finally, the main clinical indications of SPECT and PET in temporal and extratemporal epilepsy are detailed.

Alpha-Methyl-l-Tryptophan Positron Emission Tomography in Epilepsy With Cortical Developmental Malformations

Preliminary studies suggest that alpha[(11)C]methyl-l-tryptophan positron emission tomography can detect the epileptic focus within malformations of cortical development. We determined the sensitivity and specificity of alpha-[(11)C]methyl-l-tryptophan positron emission tomography in identifying epileptic focus in children with intractable, neocortical epilepsy with and without malformations of cortical development. Seventy-three epileptic children were classified into lesional and nonlesional groups, and compared regarding focal increased alpha-[(11)C]methyl-l-tryptophan uptake. The sensitivity and specificity of focal increased alpha-[(11)C]methyl-l-tryptophan uptake, using intracranial electroencephalogram localization of seizure onset as the standard, were compared between lesional and nonlesional groups. The specificity of alpha-[(11)C]methyl-l-tryptophan positron emission tomography for detecting seizure onset lobe was equally high in lesional (97%) and nonlesional groups (100%), whereas sensitivity was higher in the lesional than the nonlesional group (47% versus 29%; P = 0.047). The incidence of alpha-[(11)C]methyl-l-tryptophan uptake abnormality was higher in the lesional than the nonlesional group (P < 0.01). Alpha-[(11)C]methyl-l-tryptophan positron emission tomography localized and visualized epileptogenic regions in 25% of patients with nonlocalizing magnetic resonance imaging. Although overall sensitivity of alpha-[(11)C]methyl-l-tryptophan positron emission tomography in identifying neocortical epileptic focus is modest, specificity is extremely high. When an alpha-[(11)C]methyl-l-tryptophan focus is detected, it likely represents the epileptogenic region to be resected.

Positron emission tomography in neurological diseases

Positron emission tomography (PET) is the study of human physiology by electronic detection of positron-emitting radiopharmaceuticals. It is one of the noninvasive technologies that can measure the metabolic and functional activity of living tissue. Positron emission tomography finds its clinical applications in broadly three specialties--oncology, cardiology, and neurology. The current review focuses on its indications in neurological diseases. Recently published literature on the use of PET in neurology has been thoroughly analyzed. Several reports regarding the usage of PET in epilepsy, stroke, dementia, and movement disorders are available. Positron emission tomography does not appear to be useful as a primary or sole imaging technique in these conditions. On the other hand, it is useful in very specific situations, which have been elaborated in the review. It is also noteworthy that PET is complementary to the computed tomography/magnetic resonance imaging findings and data obtained from combining these modalities can be valuable in situations such as localization of the epileptogenic focus in cases of refractory epilepsy or for prediction of the outcome after thrombolysis in acute ischemic stroke. The major handicaps in widespread use of PET appear to be its lack of availability and its relatively high cost. Nevertheless, a review such as this would be helpful in judiciously selecting those patients who would benefit from undergoing a PET scan, at a time when PET imaging facility is likely to be available soon in the Indian private sector.

Emerging role of PET in epilepsy

To localize epileptogenic zones, preoperative evaluation of surgical candidates by F-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography (PET) has become a routine practice. Among 118 who were operated for medial temporal and neocortical epilepsies and followed up for more than a year, the sensitivity of FDG PET was 85%. In contrast, the sensitivity of MRI or ictal SPECT was only 75%. FDG PET is helpful in medial temporal lobe epilepsy (TLE), particularly in those patients with ambiguous sclerosis, in patients with bilateral sclerosis and/or atrophy and in those patients with normal MRI findings. About one third to one half of intractable patients are usually suspected to have neocortical epilepsy. According to our previous study, positive predictive value of FDG PET in cryptogenic epilepsy is over 70%. Among the complex partial seizure patients, lateral temporal lobe or frontal lobe epilepsies are relatively easy to diagnose. The sensitivity of FDG PET was 36% in patients without structural lesions on MRI and 73% in patients with structural lesions in frontal lobe epilepsy. As for the occipital lobe epilepsy, the localization rate was found to be 47% by MRI and 60% by PET. Statistical parametric mapping (SPM) is a voxel-based approach for determining the significantly different area from normal controls. The quantification method using automatic volume of interval on population-based atlas (statistical probabilistic anatomical map; SPAM) was first used to objectively quantify the asymmetric index, and these asymmetric indices could be used to localize epileptogenic zones on FDG PET for evaluation of the extent and severity of hypometabolism. In conclusion, FDG PET is helpful to localize epileptogenic zones, especially in patients with non-lesional epilepsy on MRI. Quantitative methods, such as SPM and SPAM, are believed to be able to enhance the objectivity of the analysis to find epileptogenic zones by revealing hypometabolic areas.