Factors affecting bilateral temporal lobe hypometabolism on 18F-FDG PET brain scan in unilateral medial temporal lobe epilepsy Supatporn Tepmongkol a, ⁎, Teeradej Srikijvilaikul b , Pataramon Vasavid a a Nuclear Medicine Division, Department of Radiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand b Department of Neurology, Prasat Neurological Institute, Bangkok, Thailand abstract article info Article history: Received 10 July 2013 Revised 16 August 2013 Accepted 17 August 2013 Available online 26 September 2013 Keywords: Temporal lobe epilepsy Bitemporal Positron emission tomography Epilepsy imaging Seizure localization Hypometabolism Epileptogenic zone Functional deficit zone Seizure duration Bilateral temporal lobe hypometabolism (BTH) on 18 F-FDG PET brain scan is frequently seen in unilateral medial temporal lobe epilepsy (mTLE). This study aimed to identify the factors that influence BTH in patients with mTLE in order to minimize the significant factor(s) prior to performing a FDG-PET brain scan. Forty patients with uni- lateral mTLE who underwent 18 F-FDG PET scan for presurgical epilepsy workup were included. Bilateral temporal lobe hypometabolism of the anterior and medial parts of the temporal lobe was identified by a semiquantitative visual scale. Lateralization of TLE was identified by either intracranial EEG (22/40 cases) and/or improvement of seizure 2 years after temporal lobectomy (37/40 cases). The factors analyzed included basic demographic char- acteristics (age, sex, occupation, years of education, and handedness), history related to seizure (age at epilepsy onset and epilepsy duration, history of febrile seizure and head injury, frequency of seizure with impaired cogni- tion in the last 3 months, presence of secondarily generalized tonic–clonic seizure, automatism side, presence of postictal confusion, and side of MRI temporal abnormality), information during video-EEG monitoring (clinical lateralization, interictal scalp EEG lateralization (interictal epileptiform discharge), and ictal scalp EEG lateraliza- tion), and information during the FDG-PET study (duration from the last seizure (≤2 days or N 2 days), last sei- zure type, and the presence of slow waves or sharp waves during the FDG uptake period). Significant factors related to BTH were analyzed using multivariate analysis. Only the ≤2-day duration from the last seizure to the PET scan shows a significant effect (p = 0.021) on BTH finding with 15 times greater incidence compared to a duration N 2 days. Bilateral temporal lobe hypometabolism, which causes conflict in lateralizing the epilep- togenic zone in temporal lobe epilepsy, can be avoided by performing PET scan more than 2 days after the last seizure. © 2013 Elsevier Inc. All rights reserved. 1. Introduction Positron emission tomography (PET) is a functional imaging tech- nique that reflects functional deficit area(s) which incorporates the epileptogenic zone and seizure-spreading areas [1,2]. In intractable temporal lobe epilepsy (TLE), unilateral ictal onset from all presurgical data led to good surgical outcome. In some cases though, PET may be required when there is incongruent presurgical data. A finding of unilat- eral temporal lobe hypometabolism (UTH) on PET highly correlates with the epileptogenic zone in TLE and, thus, identifies the side of tem- poral lobectomy [3,4]. However, PET may show bilateral temporal lobe hypometabolism (BTH) in some patients with unilateral temporal lobe epilepsy. The presence of BTH leads to inconclusive results in temporal lobectomy side identification. Although previous studies suggest that there are several factors shown to influence BTH [5–12], most studies did not focus on patients with unilateral temporal lobe epilepsy with BTH therefore limiting the use of FDG-PET in this patient group. This study thus aimed to identify and evaluate all possible factors that influ- ence bilateral temporal lobe hypometabolism on 18 F-FDG PET/CT brain scan in order to minimize the significant factor(s) prior to the FDG- PET scan of the brain in patients with temporal lobe epilepsy. 2. Methods 2.1. Patients The study was approved by the Institutional Review Board of the Fac- ulty of Medicine, Chulalongkorn University. All patients with intractable temporal lobe epilepsy set to undergo positron emission tomography using 18 F-fluorodeoxyglucose (FDG-PET) at the PET/CT Center, Nuclear Medicine Division, Department of Radiology, King Chulalongkorn Memorial Hospital from December 2006 to December 2010 were identified. There were 76 patients with TLE who underwent FDG-PET. Epilepsy medical records from the Chulalongkorn Comprehensive Epi- lepsy Center (CCEP) as well as medical records from the hospital's files were retrospectively reviewed. Patients who underwent FDG-PET and had medial temporal lobe epilepsy with unilateral temporal ictal Epilepsy & Behavior 29 (2013) 386–389 ⁎ Corresponding author. Fax: +66 2 2564162. E-mail address: supatporn@hotmail.com (S. Tepmongkol). 1525-5050/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yebeh.2013.08.017 Contents lists available at ScienceDirect Epilepsy & Behavior journal homepage: www.elsevier.com/locate/yebeh