Abstract

Unlike interictal Positron Emission Tomography (PET), ictal PET is not regularly used in the study of refractory focal epilepsy, and its usefulness in presurgical evaluations, and prognosis value have not been established. The aim is to present six patients with epilepsy whose PET/CT brain scans showed focal hypermetabolism, and analyze their correlation with the histopathological findings and clinical results. We reviewed 146 18F-FDG PET/CT scans performed on patients with refractory focal epilepsy. Only those cases with hypermetabolic foci which were subsequently surgically resected were selected. The epidemiological and clinical data were reviewed in addition to the brain MRI, Electroencephalography (EEG), video-EEG monitoring, intraoperative Electrocorticography (ECoG), histopathology, and postsurgical outcome. The PET findings were correlated with the clinical characteristics of the seizures, the EEG, brain MRI, ECoG, and histopathology. Seven PET/CT scans carried out on six patients showed well-defined hypermetabolic foci (three temporal, four extratemporal). There was a high correlation between the clinical lateralization, EEG/ECoG findings, and hypermetabolic foci located by PET. An MRI correctly identified the resected histopathological lesion in five cases and it was negative in two. Three patients had Focal Cortical Dysplasia (FCD), one had FCD with areas of polymicrogyria, one had temporal lobe cavernoma associated with hippocampal sclerosis, and one had a focal subcortical heterotopia. Mean postsurgical follow-up was 29.1 months (range: 16-24 months) and all patients were seizure free during this period. This small series of patients who underwent surgery for intractable focal epilepsy have shown good correlation between the ictal F18-FDG PET/CT scan and the electroclinical and pathological findings. These results suggest that hypermetabolic foci showed in PET/CT provides a reliable estimation of epileptogenic zone. Focus size underestimation in one case suggest the need of doing an interictal PET before surgery.

Highlights

  • Positron Emission Tomography (PET) of the brain plays an important role in the study of patients with drug-resistant focal epilepsy since it helps identify epileptogenic foci in non-lesional cases

  • The purpose of this study is to report seven ictal 18F-FDG PET/CT studies performed on six patients with refractory focal epilepsy that presented focal brain glucose hypermetabolism, and analyze their correlation with the histopathological findings and clinical results

  • Isotopic techniques are of great help in determining the epileptogenic zone and they are mainly represented by ictal SPECT (Single Photon Emission Computed Tomography) and the interictal PET [10]

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Summary

Introduction

Positron Emission Tomography (PET) of the brain plays an important role in the study of patients with drug-resistant focal epilepsy since it helps identify epileptogenic foci in non-lesional cases. The study is normally carried out during the interictal phase (without clinical seizures) when a cortical area with a reduced glucose uptake can be observed. The sensitivity of interictal PET with 18F-FDG for lateralization of focus is 80-90% in temporal epilepsy and 50-70% in extratemporal epilepsy, higher than a MRI in cases of cortical dysplasia [1,2,3]. Several authors have reported the occurrence of clinical or electrographic seizures while the PET is being performed, associated with hypermetabolic areas of the brain (meaning, a higher uptake of glucose) and this has been given the name of ictal PET [4,5]. The purpose of this study is to report seven ictal 18F-FDG PET/CT studies performed on six patients with refractory focal epilepsy that presented focal brain glucose hypermetabolism, and analyze their correlation with the histopathological findings and clinical results

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