Contralateral temporal hypometabolism on positron emission tomography in temporal lobe epilepsy

Introduction — No detailed case studies report lateralised hypometabolism on positron emission tomography (PET) contralateral to the epileptogenic focus in temporal lobe epilepsy (TLE). Material and methods — We performed ¹⁸F fluorodeoxyglucose (FDG) PET in two intractable TLE patients. Results — One had right temporal interictal spikes on electroencephalography (EEG) and a right medial temporal lobe lesion on magnetic resonance imaging (MRI). FDG-PET showed decreased uptake in the left temporal lobe. Right temporal ictal onset, with bilateral interictal epileptiform activity, occurred on intracranial EEG. He is seizure free after right temporal lobectomy and ganglioglioma resection. The second had right temporal lobe interictal and ictal EEG activity. MRI demonstrated right anteriomedial temporal increased T2 signal. Neuropsychology revealed bilateral cognitive dysfunction. FDG-PET showed left anterior temporal and lateral frontal hypometabolism. He is seizure free after right temporal lobectomy. Conclusion — These findings suggest that regional uptake asymmetry on FDG-PET may be give misleading lateralising information in TLE.     

FDG-Positron Emission Tomography and Invasive EEG: Seizure Focus Detection and Surgical Outcome

Summary: Purpose : To study the value of [¹⁸F]2-deoxyglucose (FDG)-positron emission tomography when surface ictal EEG is nonlocalizing.
Methods : FDG-PET scans were performed in 46 patients with complex partial seizures (CPS) not localized by ictal SUT-face-sphenoidal video-EEG (VEEG) telemetry. Interictal PET was performed with continuous EEG monitoring, and images were analyzed with a standard template. Forty patients subsequently had subdural and 6 had depth electrodes (invasive EEG, IEEG); 22 had bilateral implants. A focus was detected in 40, and 35 had temporal lobectomy based on IEEG localization.
Results : There was a close association between IEEG and PET localization (p < 0.01): 26 patients had relative unilateral temporal FDG-PET hypometabolism, all had congruent IEEG, and 18 of 23 were seizure-free after temporal lobectomy. Five patients had unilateral frontotemporal hypometabolism (3 of 5 were seizure-free), 1 had frontal hypometabolism, and 14 had no lateralized PET abnormality (4 of 7 were seizure-free). Patients who became seizure-free had significantly higher lateral temporal asymmetry index (AI). PET showed 315% relative temporal hypometabolism (AI) in 12 of 22 patients with non-lateralized surface ictal VEEG and was capable of distinguishing between frontal and temporal foci in 16 of 24 patients with lateralized, but not localized, surface ictal video-EEG.
Conclusions : FDG-PET provides valuable data in patients with unlocalized surface ictal EEG and can reduce the number of patients who require IEEG studies. Quantitation is necessary for optimal PET interpretation.     

Non-invasive examinations successfully select patients with medial temporal lobe epilepsy for anterior temporal lobectomy]

We retrospectively analyzed 8 patients with intractable medial temporal lobe epilepsy (MTLE) who underwent the anterior temporal lobectomy with hippocampectomy (ATL) without invasive examinations such as chronic subdural electrode recording. Five patients had a history of febrile convulsion. While all 8 patients had oral automatism, automatism of ipsilateral limbs with dystonic posture of contralateral limbs was demonstrated in 2 patients. Bilateral temporal paroxysmal activities on interictal EEG was observed in 4 patients and all patients had clear ictal onset zone on unilateral anterior temporal region. MRI demonstrated unilateral hippocampal sclerosis in 5 cases. Interictal FDG-PET depicted hypometabolism of the unilateral temporal lobe in all cases, however, ECD-SPECT failed to reveal the hypoperfusion of the unilateral temporal lobe in a case. Postoperatively, 7 cases became seizure free, and one had rare seizure. Non-invasive examinations, especially ictal EEG and concordant FDG-PET findings, in patients with oral automatism in seizure semiology, successfully select patients with MTLE for ATL.     

Regional brain glucose metabolism in patients with complex partial seizures investigated by intracranial EEG.

We performed interictal 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (18FDG-PET) studies in 57 patients with complex partial epilepsy (CPE), not controlled by medical treatment and considered for surgical resection of their epileptic focus. A precise localization of the epileptic focus was obtained in 37 of these patients with a combination of subdural and depth electrodes. We visually inspected the metabolic images; we also measured glucose consumption in a number of brain regions and compared the values with those obtained in 17 normal controls. Eighty-two percent of the 57 patients had an area of glucose hypometabolism on the 18FDG-PET images. Six patients had a frontal epileptic focus, 3 of them had a frontal lobe hypometabolism. Twenty-six patients had a unilateral temporal lobe focus and all of them displayed a temporal lobe hypometabolism. The asymmetry was more pronounced in the lateral temporal cortex (-20%) than in the mesial part of the temporal lobe (-9.6%). In each cortical brain region on the side of the epileptic focus (except the sensorimotor cortex), glucose consumption rate was lower than in the contralateral region or than in controls. No differences could be found between patients with a seizure onset restricted to the hippocampus and patients with a seizure onset involving the hippocampus and the adjacent neocortex. Divergent metabolic patterns were obtained in 5 patients with bilateral temporal seizure foci. Combined with other non invasive techniques (EEG, neuroradiology), PET contributes increasingly to the selection of patients with CPE who could benefit from surgical treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative study of interictal PET and ictal SPECT in complex partial seizures

Objective – To compare the sensitivity of ictal ^99mTc-HMPAO single photon emission computed tomography (SPECT) with interictal ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) in localization of the epileptogenic focus in patients with medically intractable complex partial seizures (MI-CPS). Material and methods – Retrospective analysis was performed on patients with MI-CPS who underwent anterior temporal lobectomy from January 1993 onwards when PET became available to us for clinical studies at the Indiana University Medical Center. There were 38 female and 29 male patients (total=67) with MI-CPS, 10 to 55.5 years of age (mean 31) and duration of their epilepsy from 1-46 years (mean 21). Interictal PET was evaluated for evidence of focal hypometabolism and ictal SPECT for focal perfusion abnormality (hyperperfusion or hypoperfusion) by visual analysis. Results – Both Ictal SPECT and interictal FDG-PET studies were obtained in 36 patients with MI-CPS. PET showed definite hypometabolism in 30 and questionable hypometabolism in an additional two patients. Ictal SPECT correctly localized the seizure focus in 27 patients by demonstrating ictal hyperperfusion whereas in one the hyperperfusion was falsely localized. In an additional seven patients the ictal SPECT provided probable localization by demonstrating ictal hypoperfusion in the appropriate temporal lobe. The sensitivity of ictal SPECT and interictal PET was 34/36 and 32/36, respectively, the difference was not statistically significant (χ²_y=0.18, DF=1, P=0.67). In six of the 36 patients the two tests were complementary to each other in providing localizing information. Conclusion – Ictal SPECT and interictal PET are equally sensitive and reliable techniques in localizing the epileptogenic focus in patients with MI-CPS. They play a critical role in providing localization in MRI negative patients allowing surgical resection to be undertaken in many without additional invasive electrographic monitoring.     

Positron emission tomographic measurement of cerebral blood flow and temporal lobectomy

We used positron emission tomography (PET) and bolus injection of H₂¹⁵O to measure interictal cerebral blood flow (CBF) in 32 patients who had temporal lobectomy for uncontrolled complex partial seizures. Seizure focus localization was confirmed by ictal video–electroencephalographic (video-EEG) telemetry, and patients who had imaging findings suggesting the presence of a tumor were excluded. PET-CBF studies were interpreted using a standard template by raters blinded to EEG and clinical data, and were not used in surgical planning. After surgery, patients were followed for 32 ± 18 months. Twenty-six patients were seizure free and 6 had persistent seizures. Mean lateral temporal hypoperfusion was 8 ± 14% in patients who became seizure free and 9 ± 6% in patients with persistent seizures. Fourteen patients had at least 15%, and 11 at least 20% hypoperfusion, but were not more likely to be seizure free. Three additional patients had 15 to 20% hypoperfusion in the temporal lobe contralateral to their EEG focus. PET measurement of CBF using bolus H₂¹⁵O should not be used to help select patients for temporal lobectomy.     

Complex partial seizures. Correlation of clinical and metabolic features

We compared metabolic patterns on 18F-2-deoxyglucose positron emission tomography (PET) with closed circuit television and simultaneous electroencephalographic ictal recordings of complex partial seizures in 48 patients. Closed circuit television and electroencephalographic data and PET scans were scored by "blinded" raters. Of the 48 patients, 26 had unilateral temporal; three, frontal; ten, ipsilateral frontotemporal; one, frontoparietal; and five, temporoparietal hypometabolism; and three had widespread hypometabolism affecting frontal, temporal, and parietal lobes. patients with frontal hypometabolism alone had shorter ictal and postictal durations, but involvement of multiple regions was associated with prolonged seizures. Auras were more likely to be present in patients with temporal hypometabolism alone, but an initial motionless stare did not distinguish this group. However, other metabolic patterns did not predict specific ictal clinical features. Vocalizations (formed or unformed) were not more closely associated with frontal involvement. When hypometabolism is multilobar, it may be difficult to use PET to distinguish between complex partial seizures of frontal and temporal origin.     

Comparison of the intracarotid amobarbital procedure and interictal cerebral 18-fluorodeoxyglucose positron emission tomography scans in refractory temporal lobe epilepsy.

The relationship between interictal focal hypometabolism determined by 18-fluorodeoxyglucose positron emission tomography (FDG-PET) scans and memory function with the intracarotid amobarbital procedure (IAP) was evaluated in 23 patients with temporal lobe epilepsy. All patients underwent prolonged EEG/video monitoring. The epileptogenic focus was defined by interictal epileptiform discharges and ictal onsets. All 23 patients had recorded seizures arising exclusively from one temporal lobe. PET showed temporal lobe hypometabolism ipsilateral to the epileptogenic focus in 86% (20 of 23) of patients; IAP showed impaired memory of the hemisphere of seizure onset in 65% (15 of 23). Sixty-five percent (13 of 20) of patients with focal hypometabolism had ipsilateral memory impairment. Memory impairment contralateral to the hypometabolic zone was not observed. Ninety-five percent (22 of 23) of patients demonstrated functional impairment by either PET or IAP (or both) on the epileptogenic side.     

Prognostic factors in neocortical epilepsy surgery: multivariate analysis

PURPOSE: Defining prognostic factors for neocortical epilepsy surgery is important for the identification of ideal candidates and for predicting the prognosis of individual patients. We use multivariate analysis to identify favorable prognostic factors for neocortical epilepsy surgery. METHODS: One hundred ninety-three neocortical epilepsy patients, including 91 without focal lesions on MRI, were included. Sixty-one had frontal lobe epilepsy (FLE), 80 had neocortical temporal lobe epilepsy (nTLE), 21 had parietal lobe epilepsy (PLE), and 22 had occipital lobe epilepsy (OLE). The primary outcome variable was patient status >or=2 years after surgery (i.e., seizure free or not). Clinical characteristics and the recent presurgical diagnostic modalities were considered as probable prognostic factors. Univariate and standard multiple logistic regression analyses were used to identify favorable prognostic factors. RESULTS: The seizure-free rate was 57.5%. By univariate analysis, a focal lesion on MRI, localized ictal onset on surface EEG, epilepsies other than FLE, localized hypometabolism on fluorodeoxyglucose-positron emission tomography (FDG-PET), and pathologies other than cortical dysplasia were significantly associated with a seizure-free outcome (p<0.05). Multivariate analysis revealed that a focal lesion on MRI (p=0.003), correct localization by FDG-PET (p=0.007), and localized ictal onset on EEG (p=0.01) were independent predictors of a good outcome. CONCLUSIONS: The presence of a focal lesion on MRI, correct localized hypometabolism on FDG-PET, or localized ictal rhythms on EEG were identified as predictors of a seizure-free outcome. Our results suggest that these findings allow the selection of better candidates for neocortical epilepsy surgery.     

The prognostic value of [F]FDG-PET in nonrefractory partial epilepsy

PURPOSE: Regional abnormalities of cerebral glucose metabolism, as identified by 18-fluorodeoxyglucose positron emission tomography (FDG-PET) have prognostic value regarding the outcome of epilepsy surgery in patients with refractory partial epilepsy. The value of FDG-PET abnormalities in nonrefractory patients has not been investigated systematically. This study examines whether FDG-PET could be used for early identification of nonrefractory epilepsy in patients who will become pharmacoresistant later during the course of their disease. METHODS: We investigated interictal abnormalities of cerebral glucose metabolism by using FDG-PET in 125 consecutive patients with nonrefractory cryptogenic partial epilepsy and normal cranial magnetic resonance imaging (MRI), and we compared relative changes in seizure frequency in 90 patients after > or =2 years of follow-up. RESULTS: Regional asymmetry of tracer distribution was seen in 43 of the 90 patients. Forty-one patients had regional glucose hypometabolism in the temporal and two patients in an extratemporal region. No difference between patients with and without a hypometabolic focus was found regarding seizure freedom after follow-up. This held true also for the subgroup of patients with epilepsy onset within 1 year before admission. Only patients with regional glucose metabolism showed an increase in seizure frequency. Multivariate analysis showed that only anticonvulsive treatment before index admission and the possibility of localizing the epileptogenic focus by using all available clinical and EEG data were independently associated with continuing seizures after a median follow-up period of 43 months. CONCLUSIONS: Regional hypometabolism in FDG-PET is not significantly associated with a lower likelihood of successful anticonvulsant drug therapy in patients with nonrefractory partial epilepsy. Careful analysis of all routinely available clinical and neurophysiologic data has a much better predictive power to identify patients with medically refractory epilepsy early in the course of the disease. However, if PET data are available, they could help in identifying patients with a less benign course.     

Relationship between preoperative hypometabolism and surgical outcome in neocortical epilepsy surgery

Purpose: Fluorine‐18‐fluorodeoxyglucose–positron emission tomography (FDG‐PET) hypometabolism has been used to localize the epileptogenic zone. However, glucose hypometabolism remote to the ictal focus is common and its relationship to surgical outcome has not been considered in many studies. We investigated the relationship between surgical outcome and FDG‐PET hypometabolism topography in a large cohort of patients with neocortical epilepsy. Methods: We identified all patients (n = 68) who had interictal FDG‐PET between 1994 and 2004 and who underwent resective epilepsy surgery with follow up for more than 2 years. The volumes of significant FDG‐PET hypometabolism involving the resected epileptic focus and its surrounding regions (perifocal hypometabolism) and those distant to and not contiguous with the perifocal hypometabolism (remote hypometabolism) were determined statistically using Statistical Parametric Mapping (voxel threshold p = 0.01, extent threshold ≥250 voxels, uncorrected cluster‐level significance p < 0.05) and were compared with magnetic resonance imaging (MRI) and clinical and demographic variables using a multiple logistic regression model to identify independent predictors of seizure outcome. Key Findings: Remote hypometabolism was present in 39 patients. Seizure freedom was 49% (19 of 39 patients) in patients with glucose hypometabolism remote from the epileptogenic zone compared to 90% (26 of 29 patients) in patients without remote hypometabolism. In 43 patients with an MRI‐identified lesion, seizure freedom was 79% (34 of 43 patients). In patients with normal MRI, cortical dysplasia was the predominant pathologic substrate. Multiple logistic regression analysis identified a larger volume of significant remote hypometabolism (p < 0.005) and absence of a MRI‐localized lesion (p = 0.006) as independent predictors of continued seizures after surgery. Significance: In patients with widespread glucose hypometabolism that is statistically significant when compared to controls, epilepsy surgery may not result in complete seizure freedom despite complete removal of the MRI‐identified lesion. The volume of significant glucose hypometabolism remote to the ictal‐onset zone may be an independent predictor of the success of epilepsy surgery.     

Focal functional deficits in temporal lobe epilepsy on PET scans and the intracarotid amobarbital procedure: comparison of patients with unitemporal epilepsy with those requiring intracranial recordings

PURPOSE: To analyze the relationship between the intracarotid amobarbital procedure (IAP) and positron emission tomography (PET) and study the lateralizing value of these tests in patients with unitemporal epilepsy and those requiring intracranial recordings. METHODS: We compared 51 patients with unitemporal epilepsy (group1) with 26 patients in whom surface recordings failed to reveal a distinct unitemporal focus, necessitating invasive recordings (group 2). RESULTS: The brain magnetic resonance imaging (MRI) scans for group 1 showed mesial temporal sclerosis in 70.5% of the patients. PET showed unilateral temporal hypometabolism in 88%. In addition, 74.5% of the patients in group 1 had impaired memory on the epileptogenic side on the IAP, and 89.4% of those patients also had ipsilateral temporal hypometabolism on PET scans. All the group 1 patients underwent temporal resections. The pathologic examination showed hippocampal sclerosis in 72% of the patients. Eighty percent of group 1 patients became seizure free, and 16% had rare seizures (follow-up, 2-7 years). MRIs for group 2 showed mesial temporal sclerosis in 31% of the patients; PET scans showed temporal hypometabolism in 39%. The IAP was lateralized in 47.8%. Sixty-nine percent had temporal lobe resections. The pathologic examination showed hippocampal sclerosis in 44% of the patients. Forty-four percent of group 2 patients became seizure free, and 27.7% had rare seizures (follow-up, 2-8 years). CONCLUSIONS: Ninety-six percent of the patients with unitemporal foci had focal functional deficits on the epileptogenic side on 18-fluorodeoxyglucose-(FDG) PET scans, the IAP, or both. The results of the FDG-PET were predictive of impaired memory on the IAP. Memory impairment contralateral to the temporal hypometabolism found on the PET scans was never seen. These patients had an excellent outcome. In contrast, <50% of the patients requiring intracranial recordings had focal functional deficits, suggesting that more a diffuse pathology may account for their less favorable outcome.     

Presurgical evaluation for partial epilepsy: relative contributions of chronic depth-electrode recordings versus FDG-PET and scalp-sphenoidal ictal EEG

One hundred fifty-three patients with medically refractory partial epilepsy underwent chronic stereotactic depth-electrode EEG (SEEG) evaluations after being studied by positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) and scalp-sphenoidal EEG telemetry. We carried out retrospective standardized reviews of local cerebral metabolism and scalp-sphenoidal ictal onsets to determine when SEEG recordings revealed additional useful information. FDG-PET localization was misleading in only 3 patients with temporal lobe SEEG ictal onsets for whom extratemporal or contralateral hypometabolism could be attributed to obvious nonepileptic structural defects. Two patients with predominantly temporal hypometabolism may have had frontal epileptogenic regions, but ultimate localization remains uncertain. Scalp-sphenoidal ictal onsets were misleading in 5 patients. For 37 patients with congruent focal scalp-sphenoidal ictal onsets and temporal hypometabolic zones, SEEG recordings never demonstrated extratemporal or contralateral epileptogenic regions; however, 3 of these patients had nondiagnostic SEEG evaluations. The results of subsequent subdural grid recordings indicated that at least 1 of these patients may have been denied beneficial surgery as a result of an equivocal SEEG evaluation. Weighing risks and benefits, it is concluded that anterior temporal lobectomy is justified without chronic intracranial recording when specific criteria for focal scalp-sphenoidal ictal EEG onsets are met, localized hypometabolism predominantly involves the same temporal lobe, and no other conflicting information has been obtained from additional tests of focal functional deficit, structural imaging, or seizure semiology.     

Surgical treatment of West syndrome.

The discovery of focal or multifocal cortical lesions using magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning in the majority of infants with West syndrome has led to a surgical approach in the treatment of some patients with intractable infantile spasms. The locations of these lesions should be concordant with localization of focal ictal and/or interictal electroencephalographic (EEG) abnormalities prior to proceeding with cortical resection. When a single lesion is present on the MRI or PET, and there is good correlation with EEG localization, surgical treatment is generally quite favorable in terms of both seizure control and cognitive development. Interictal glucose metabolism PET scans in children with intractable cryptogenic infantile spasms show unifocal cortical hypometabolism in about 20% of cases. In the majority, however, multifocal asymmetric hypometabolism is suggestive of multifocal underlying lesions, possibly multifocal cortical dysplasia. When the pattern of glucose hypometabolism is symmetric, a lesional etiology is less likely, thus neurometabolic or neurogenetic disorders should be considered. Therefore, the pattern of glucose hypometabolism on PET in infants with intractable cryptogenic spasms is a useful guide to decide whether a medical or surgical approach should be undertaken. In order to achieve the best cognitive outcome with surgery, it is important to resect the entire 'nociferous' area rather than just the seizure focus. Our research with new PET imaging probes has attempted to provide a comprehensive evaluation of the epileptogenic zone including the 'nociferous' cortex. We have used [(11)C]flumazenil (FMZ), which labels gamma aminobutyric acid(A) (GABA(A)) receptors, and have found this to be particularly useful in showing: (i) decreased receptor binding with medial temporal involvement thus indicating resection of medial temporal structures, (ii) the peri-lesional epileptogenic zone surrounding MRI lesions, (iii) the seizure onset zone in MRI-negative cases, and (iv) potential secondary epileptic foci. Another recently developed PET probe, alpha[(11)C]methyl-L-tryptophan (AMT) which is a precursor for the serotonin and the kynurenine metabolism pathways, is capable of differentiating between epileptogenic and non-epileptogenic tubers in patients with tuberous sclerosis complex and intractable epilepsy (including infantile spasms). Subsequently, we have applied AMT PET in patients with multifocal cortical dysplasia to determine the predominant seizure focus, and the results have been promising with regard to seizure control but not cognitive development. Thus, the introduction of newer more specific PET probes for epilepsy has led to improved and more accurate localization of seizure foci that should ultimately improve outcome of epilepsy surgery in West syndrome.     

Preoperative FDG-PET temporal lobe hypometabolism and verbal memory after temporal lobectomy

OBJECTIVE: To examine the relationship of preoperative fluorodeoxyglucose (FDG)-PET asymmetry in temporal lobe metabolism and memory outcome after anterior temporal lobectomy (ATL). METHODS: In a university-based epilepsy surgery center, 60 ATL patients (27 left, 33 right) were divided into two groups: no/mild (n = 21) or moderate/ severe (n = 39) asymmetry in temporal lobe hypometabolism as determined by FDG-PET. All patients were nonretarded, at least 18 years of age, left-hemisphere speech dominant, without MRI abnormalities other than hippocampal atrophy, and with unilateral temporal lobe origin of intractable complex partial seizures. Neuropsychological measures of intelligence and verbal and visual memory function were assessed preoperatively and 6 months postoperatively. RESULTS: Left ATL patients with no/mild asymmetry in FDG-PET temporal lobe metabolism exhibited significantly greater verbal memory decline compared with left ATL patients with moderate/severe hypometabolism. There was no significant relationship between PET asymmetry and pre- to postsurgical IQ change. No significant relationship was observed between extent of PET hypometabolism and memory outcome for right ATL patients. CONCLUSIONS: FDG-PET asymmetry can be added to the preoperative clinical markers that appear useful in predicting verbal memory decline after left ATL.     

Persistent postictal hyperperfusion demonstrated with PET

Four patients with complex partial seizure disorder whose positron emission tomography (PET) scans show sustained hyperperfusion of the epileptiform focus 12-24 h after a seizure episode are presented. Three of these patients underwent same day Fluorine-18 (18F) deoxyglucose (FDG) PET scans, which showed hypometabolism of the epileptic temporal lobe. In one patient who underwent repeated blood flow and concurrent glucose metabolism scans 4 days after a seizure, hyperperfusion was not present and the FDG-PET demonstrated hypometabolism. Persistent hyperperfusion was noted in six out of 65 cases studied. Four out of six patients who were followed clinically were presented in this report. The cause of the rare occurrence of persistent postictal or interictal hyperperfusion and the differences of postictal blood flow dynamics and glucose metabolism need to be clarified further with future studies.     

Comparison of ictal SPECT and interictal PET in the presurgical evaluation of temporal lobe epilepsy

We retrospectively compared ictal technetium 99m hexamethylpropyleneamineoxime single-photon emission computed tomography (SPECT) and interictal ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) in 35 patients with well-lateralized temporal lobe epilepsy (TLE). Based on SPECT scans the two observers correctly lateralized seizure foci with certainty in 89% of patients; interobserver agreement was excellent. Both observers incorrectly lateralized the seizure focus on two SPECT scans; one error was explained by rapid electroencephalographic spread to the contralateral side and for the other patient, isotope was injected during a brief aura. Based on PET scans, observers correctly lateralized the foci with certainty in 63% and with lesser confidence in 83%; four incorrect lateralizations were made by one observer and none by the other. PET interobserver disagreement was explained by differences between observers in weighting the relative hypometabolism in medial and lateral temporal regions. The detection rate for PET was lower in the absence of structural imaging abnormalities (60 vs 87%). PET yielded correct lateralizations in the 2 patients for whom SPECT interpretation was difficult. We conclude that both ictal SPECT and interictal PET are sensitive methods for the lateralization of TLE, but SPECT can be interpreted with greater certainty and is more sensitive when magnetic resonance imaging findings are negative. False lateralization is rare with ictal SPECT and can be explained when interpreted in conjunction with electroclinical data. Both investigations have complementary roles when localization is difficult.     

Surgical outcome and prognostic factors of cryptogenic neocortical epilepsy

Surgical treatment of cryptogenic neocortical epilepsy is challenging. The aim of this study was to evaluate surgical outcomes and to identify possible prognostic factors including the results of various diagnostic tools. Eighty-nine patients with neocortical epilepsy with normal magnetic resonance imaging (35 patients with frontal lobe epilepsy, 31 with neocortical temporal lobe epilepsy, 11 with occipital lobe epilepsy, 11 with parietal lobe epilepsy, and 1 with multifocal epilepsy) underwent invasive study and focal surgical resection. Patients were observed for at least 2 years after surgery. The localizing values of interictal electroencephalogram (EEG), ictal scalp EEG, interictal 18F-fluorodeoxyglucose positron emission tomography (FDG-PET), and subtraction ictal single-photon emission computed tomography were evaluated. Seventy-one patients (80.0%) had a good surgical outcome (Engel class 1-3); 42 patients were seizure free. Diagnostic sensitivities of interictal EEG, ictal scalp EEG, FDG-PET, and subtraction ictal single-photon emission computed tomography were 37.1%, 70.8%, 44.3%, and 41.1%, respectively. Localization by FDG-PET and interictal EEG was correlated with a seizure-free outcome. The localizing value of FDG-PET was greatest in neocortical temporal lobe epilepsy. The focalization of ictal onset and also ictal onset frequency in invasive studies were not related to surgical outcome. Concordance with two or more presurgical evaluations was significantly related to a seizure-free outcome.     

Epilepsy duration, febrile seizures, and cerebral glucose metabolism

PURPOSE: Studies using magnetic resonance imaging have shown that reduced hippocampal volume is associated with a history of febrile seizures, the duration of epilepsy, and the number of generalized tonic-clonic seizures. It is uncertain whether these factors have the same influence on functional as on structural measures of the integrity of the epileptogenic zone. METHODS: We used positron emission tomography (PET) with fluorine 18 2-deoxyglucose to study 91 patients with temporal lobe seizure foci localized by ictal video-EEG. PET was performed in the awake interictal resting state with ears plugged and eyes patched. We recorded surface EEG during injection (5 mCi) and the 30-min uptake period. We used a standard template to analyze PET scans. RESULTS: A significant negative relation was found between the duration of epilepsy and hippocampal glucose metabolism ipsilateral to the epileptic focus. Patients with a history of either any febrile seizures, or complex, or prolonged febrile seizures, did not have greater hypometabolism ipsilateral to the epileptic focus than did patients without a febrile seizure history. We found no effect of generalized tonic-clonic seizure history. CONCLUSIONS: Longer epilepsy duration is associated with greater hypometabolism, suggesting that epilepsy is a progressive disease.     

Temporal lobe epilepsy with bilateral seizure origin studied by [18F]FDG-positron emission tomography

Nine patients who underwent presurgical evaluation because of medically refractory temporal lobe epilepsy (TLE) showed either unilateral, although alternating in side, or bilateral simultaneous seizure onsets in both temporal lobes (TL). EEG recordings with semi-invasive foramen ovale electrodes revealed in seven patients a predominance of seizure onset in one TL of between 50% and 88%. In two patients the majority of seizures originated simultaneously in both TL. In four patients a unilateral selective amygdalohippocampectomy resulted in a good to excellent seizure outcome without noteworthy memory deficits and confirmed the preoperative lateralization of the primary epileptogenic focus by interictal ¹⁸F-fluorodeoxyglucose positron emission tomography (PET). Five patients were rejected from surgery due to strong bilaterality of their epilepsy and/or divergent presurgical findings. PET contributed to the decision of whether surgery should be performed: all patients who underwent surgery had a unilateral TL hypometabolism which was concordant with the findings of other tests. Patients in whom surgery was denied had either bilateral temporal hypometabolism or the PET findings were discordant with other results obtained during the presurgical evaluation.