Significance of interictal bilateral temporal hypometabolism in temporal lobe epilepsy

OBJECTIVE: To assess the clinical implications and the pathophysiologic determinants of interictal bitemporal hypometabolism (BTH) in temporal lobe epilepsy (TLE) not associated with bilateral MRI abnormalities or intracranial space-occupying lesions. METHODS: The authors compared the clinical, interictal, and ictal EEG, Wada test, and neuropsychology data of 15 patients with intractable complex partial seizures of temporal lobe origin and BTH with those of 13 consecutive patients with unilateral TLE associated with unilateral temporal hypometabolism (UTH) who remained seizure free for more than 3 years after anterior temporal lobectomy. 18F-fluorodeoxyglucose PET scans were analyzed visually and semiquantitatively, and ratios of counts in individual temporal areas to the rest of the cerebrum were compared with the corresponding values from 11 normal control subjects and with the nonepileptogenic hemisphere of the 13 patients with UTH. BTH was defined as more than 2.5 SDs below control values for two or more temporal areas on each side irrespective of any asymmetry. RESULTS: BTH reflected bilateral independent seizure onset in eight patients (53%). The topography of the metabolic depression was not a reliable predictor of epileptogenicity, but involvement of the inferior temporal gyrus was related specifically to ipsilateral seizure onset (70% sensitivity, 100% specificity). In patients with unilateral TLE, contralateral hypometabolism was associated with longer disease duration and worst memory performance during the Wada test, which amounted to global amnesia after ipsilateral injection in three patients, precluding surgical treatment. Contralateral seizure spread in the ictal EEG was significantly faster in patients with BTH. CONCLUSIONS: In TLE, symmetric or asymmetric BTH may signal bilateral independent seizure onset in approximately half the patients, especially when involving the inferior temporal gyrus. Alternatively, it may reflect an advanced stage of the disease process, characterized by a breakdown of the inhibitory mechanisms in the contralateral hemisphere, and secondary memory deficit associated with higher risk of postoperative memory decline. Patients with TLE and BTH but without bilateral MRI changes may still be operated on successfully, but surgical suitability should be proved by comprehensive intracranial EEG studies and Wada test.     

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.     

Seizure outcome after anterior temporal lobectomy and its predictors in patients with apparent temporal lobe epilepsy and normal MRI

PURPOSE: Very little reliable information is available regarding the role of anterior temporal lobectomy (ATL), optimal presurgical evaluation strategy, post-ATL seizure outcome, and the factors that predict the outcome in patients with medically refractory temporal lobe epilepsy (TLE) and normal high-resolution magnetic resonance imaging (MRI). To be cost-effective, epilepsy surgery centers in developing countries will have to select candidates for epilepsy surgery by using the locally available technology and expertise. METHODS: We reviewed the electroclinical and pathological characteristics and seizure outcome of 17 patients who underwent ATL for medically refractory TLE after being selected for ATL based on a noninvasive selection protocol without the aid of positron emission tomography (PET) or single-photon emission computed tomography (SPECT), despite a normal preoperative high-resolution MRI. RESULTS: Seven (41%) patients achieved an excellent seizure outcome; five of them were totally seizure free. An additional five (29%) patients had >75% reduction in seizure frequency. The following pre-ATL factors predicted an excellent outcome: antecedent history of febrile seizures, strictly unilateral anterior temporal interictal epileptiform discharges (IEDs), and concordant type 1 ictal EEG pattern. All the five patients with pathologically verified hippocampal formation neuronal loss were seizure free. The presence of posterior temporal, bilateral temporal, and generalized IEDs portended unfavorable post-ATL seizure outcome. CONCLUSIONS: A subgroup of patients destined to have an excellent post-ATL outcome can be selected from MRI-negative TLE patients by using history and scalp-recorded interictal and ictal EEG data. The attributes of these patients are antecedent history of febrile seizures, strictly unilateral anterior IEDs, and concordant type 1 ictal EEG pattern.     

An operated case of medial temporal lobe epilepsy associated with schizencephaly]

A 24-year-old male of medial temporal lobe epilepsy associated with schizencephaly was presented. He developed complex partial seizure after head trauma at the age of a year and 7 months, which became intractable at the age of 13 year. MRI demonstrated a schizencephalic cleft in the right peri-Rolandic area, cortical dysplasia in the right medical parietal and occipital lobes, and right hippocampal atrophy. Scalp-recorded EEG failed to localize the ictal onset zone. Interictal FDG-PET and ECD-SPECT indicated hypometabolism and hypoperfusion of the right entire temporal lobe, and ictal ECD-SPECT increased perfusion of this area. Chronic subdural electrode recording clearly demonstrated that ictal onset zone was located not on the schizencephalic cleft or its surrounding cortex but on the right medial temporal lobe. Following right anterior temporal lobectomy with hipppocampectomy, seizure control became easy. For the identification of the epileptogenic zone in patients with schizencephaly, chronic subdural electrode recording is mandatory.     

Orbito-frontal epilepsy masquerading as temporal lobe epilepsy-a case report.

Temporal lobectomy fails to control seizures in a considerable percentage of patients who do not have hippocampal sclerosis. One theoretical reason for failure of surgery is that some of these patients may in fact have extratemporal epilepsy. We present a 28-year-old woman with clinical and scalp electroencephalogram (EEG) evidence of right temporal lobe epilepsy (TLE) supported by functional imaging with interictal positron emission tomography (PET) and ictal single-photon emission computerized tomography (SPECT). An invasive EEG monitoring was prompted by the discovery of a small right orbito-frontal lesion on MRI. Monitoring documented seizure onset at the lesion, with rapid right temporal involvement. The patient was almost seizure-free after a lesionectomy. The index of suspicion of orbito-frontal epilepsy should be high in patients with apparent TLE when the scalp EEG and neuroimaging data are not congruent, or if temporal lobe pathology cannot be identified on structural imaging.     

Bilateral mesial temporal lobe epilepsy: comparison of scalp EEG and hippocampal MRI-T2 relaxometry

OBJECTIVE: Bilateral hippocampal abnormality is frequent in mesial temporal lobe sclerosis and might affect outcome in epilepsy surgery. The objective of this study was to compare the lateralization of interictal and ictal scalp EEG with MRI T2 relaxometry. MATERIAL AND METHODS: Forty-nine consecutive patients with intractable mesial temporal lobe epilepsy (MTLE) were studied with scalp EEG/video monitoring and MRI T2 relaxometry. RESULTS: Bilateral prolongation of hippocampal T2 time was significantly associated with following bitemporal scalp EEG changes: (i) in ictal EEG left and right temporal EEG seizure onsets in different seizures, or, after regionalized EEG onset, evolution of an independent ictal EEG over the contralateral temporal lobe (left and right temporal asynchronous frequencies or lateralization switch; P = 0.002); (ii) in interictal EEG both left and right temporal interictal slowing (P = 0.007). Bitemporal T2 changes were not, however, associated with bitemporal interictal epileptiform discharges (IED). Lateralization of bilateral asymmetric or unilateral abnormal T2 findings were associated with initial regionalization of the ictal EEG in all but one patient (P < 0.005), with lateralization of IED in all patients (P < 0.005), and with scalp EEG slowing in 28 (82,4%) of 34 patients (P = 0.007). CONCLUSION: Our data suggest that EEG seizure propagation is more closely related to hippocampal T2 abnormalities than IED. Interictal and ictal scalp EEG, including the recognition of ictal propagation patterns, and MRI T2 relaxometry can help to identify patients with bitemporal damage in MTLE. Further studies are needed to estimate the impact of bilateral EEG and MRI abnormal findings on the surgical outcome.     

Unitemporal vs bitemporal hypometabolism in mesial temporal lobe epilepsy

BACKGROUND: Patients with mesial temporal lobe epilepsy (TLE) often show bilateral temporal hypometabolism (BTH), but the nature of this finding has not been well established. OBJECTIVE: To compare the clinical characteristics between unitemporal hypometabolism (UTH) and BTH patients in mesial TLE. DESIGN: Cross-sectional study. SETTING: Epilepsy center at university hospital in Seoul, Korea. PATIENTS: We enrolled 95 patients with mesial TLE, 87 of whom had subsequently undergone surgery. Seizures, interictal and ictal electroencephalography (EEG), brain magnetic resonance imaging, Wada test, and neuropsychological test results were reviewed. (18)F-fluorodeoxyglucose positron emission tomography scans were interpreted visually. Patients were divided into 2 groups: UTH and BTH. RESULTS: There were 59 UTH patients and 36 BTH patients. Semiologic analysis showed that UTH patients had higher frequencies of aura and unilateral dystonic posturing, whereas BTH patients had higher frequencies of a nonlateralized bilateral ictal EEG pattern and bilateral interictal spikes. Moreover, BTH patients had more frequent symmetric Wada memory scores and white matter changes in the bilateral temporal lobes on brain magnetic resonance imaging than UTH patients. All UTH patients with bilateral TLE on scalp EEG showed unilateral seizure onset on intracranial EEG. CONCLUSIONS: The characteristic clinical findings of mesial TLE with BTH were a more frequent nonlateralized ictal EEG pattern, bitemporal interictal spikes, symmetric Wada memory score, and the anterior temporal white matter changes, and less frequent aura and unilateral dystonic posturing. Surgical outcomes were similar and good in both groups, although surgery could not be performed in 8 BTH patients (22%).     

Small temporal pole encephaloceles: A treatable cause of “lesion negative” temporal lobe epilepsy

Epilepsy due to encephaloceles of the temporal pole may be an under recognized, treatable cause of refractory temporal lobe epilepsy (TLE). We describe three adult patients initially labeled “lesion negative” TLE. In all, video–electroencephalography (EEG) revealed ictal theta in the left temporal region and positron emission tomography (PET) showed temporal lobe hypometabolism, but neuropsychology revealed preserved verbal memory. Close inspection of structural magnetic resonance imaging (MRI) suggested subtle abnormalities at the tip of the left temporal lobe. High resolution computed tomography (CT) confirmed bony defects in the inner table of the skull. 3T MRI with fine coronal and sagittal slices indicated cerebrospinal fluid (CSF) and brain tissue protruding into the defects. All proceeded to resection of the temporal tip and became seizure free. Patients with “lesion negative” TLE should have careful review of images covering the temporal pole. If encephalocele is suspected, further imaging with high‐resolution CT and MRI can be helpful. Temporal polar resection, sparing mesial structures, appears to be curative.     

Ictal magnetoencephalography in temporal and extratemporal lobe epilepsy

PURPOSE: We evaluated visual patterns and source localization of ictal magnetoencephalography (MEG) in patients with intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE). METHODS: We performed spike and seizure recording simultaneously with EEG and MEG on two patients with TLE and five patients with ETE. Scalp EEG was recorded from 21 channels (10-20 international system), whereas MEG was recorded from two 37-channel sensors. We compared ictal EEG and MEG onset, frequency, and evolution and performed MEG dipole source localization of interictal spikes and early ictal discharges and co-registered dipoles to brain magnetic resonance imaging (MRI). We correlated dipole characteristics with intracranial EEG, surgical resection, and outcome. RESULTS: Ictal MEG lateralized seizure onset in both TLE patients and demonstrated ictal onset, frequency, and evolution in accordance with EEG. Ictal MEG source analysis revealed tangential vertical dipoles in the anterolateral angle in one patient, and anterior dipoles with anteroposterior orientation in the other. Intracranial EEG revealed regional entorhinal seizure onset in the first patient. Both patients became seizure free after temporal lobectomy. In ETE, ictal MEG demonstrated visual patterns similar to ictal EEG and had concordant localization with interictal MEG in all five patients. Two patients underwent surgery. Ictal MEG localization was concordant with intracranial EEG in both cases. One patient had successful outcome after surgery. The second patient did not improve after limited resection and multiple subpial transections. CONCLUSIONS: Ictal MEG can demonstrate ictal onset frequency and evolution and provide useful localizing information before epilepsy surgery.     

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.     

发作间期PET对难治性颞叶癫痫的诊断价值

目的分析18例颞叶癫痫患者的正电子发射断层扫描(PET)结果.方法 18例难治性癫痫患者,根据临床症状、脑电图/录像脑电监测(EEG/VEEG)、MRI海马相和单光子发射计算机体层摄影(SPECT)检查诊断为颞叶癫痫.均进行PET检查,结果有16例显示不同程度的颞叶前中部和(或)内侧部的低代谢区域.所有患者均在手术显微镜下采用显微外科技术进行手术,其中右侧颞叶癫痫16例行标准前颞叶及海马杏仁核切除术,左侧颞叶癫痫2例行选择性海马杏仁核切除术.结果随诊观察6～26个月,按照Engel的疗效判断标准,结果I级(癫痫发作消失)11例,II级(极少发作)4例,III级(发作减少75%以上)2例,IV(无改变)1例.结论对于临床上怀疑为颞叶癫痫而上述常规检查方法不能明确癫痫灶者,PET能更好地帮助诊断.     

False Lateralization of Temporal Lobe Epilepsy with FDG Positron Emission Tomography

Summary: We report 2 patients in whom visual interpretation of interictal positron emission tomography (PET) with [¹⁸F]fluorodeoxyglucose (FDG) suggested false lateralization of an epileptic focus. PET scans were interpreted as showing diffuse left temporal lobe hypometabolism in 1 patient and lateral temporal hypometabolism in the other. However, seizures began in the right mesial temporal lobe in both patients, and both responded favorably to right temporal lobectomy. In 1 patient, the intra-cranial EEG showed continuous asymptomatic subclinical seizure activity emanating from the right amygdala. These limbic discharges probably caused unrecognized right temporal lobe hypermetabolism. In the other case, quantitative analysis of metabolic rates showed conflicting mesial and lateral metabolic indexes. Frequent mesial interictal discharges might have increased lateral temporal metabolism. We conclude that asymptomatic epileptiform activity may alter temporal lobe metabolism and that quantitative PET analysis helps clarify contradictory visual PET interpretations.     

Identification of Frontal Lobe Epileptic Foci in Children Using Positron Emission Tomography

Summary: Purpose: Presurgical evaluation for intractable frontal lobe epilepsy (FLE) is difficult and invasive, partly because anatomic neuroimaging studies with computed tomography (CT) and magnetic resonance imaging (MRI) typically do not show a discrete lesion. In adult patients with FLE, functional neuroimaging of glucose metabolism with positron emission tomography (PET) is less sensitive in detecting focal metabolic abnormalities than in temporal lobe epilepsy (TLE). Comparable data on children with FLE are not available. Methods: We used high-resolution PET scanning of glucose metabolism to evaluate 13 children (age 17 months to 17 years; mean age 9.5 years) with intractable FLE being considered for surgical treatment. Only children with normal CT and MRI scans were included. Results: Hypometabolism including the frontal lobe was evident in 12 of the 13 children, was unilateral in 11 of 13, and was restricted to the frontal lobe in 8 of 13. One child showed bilateral frontal cortex hypometabolism and another had anictal PET scan demonstrating unilateral frontal cortex hyper-metabolism surrounded by hypometabolism. Additional hypo–metabolic areas outside the frontal cortex were observed in 5 children in parietal and/or temporal cortex. Localization of seizure onset on scalp EEG was available in 10 children and corresponded to the location of frontal lobe PET abnormality in 8. However, in 4 of the 10 children, the extent of hypometabolism exceeded the epileptogenic region indicated by ictal EEG. In 2 of the 13 children, the abnormality evident on EEG was more extensive than that evident on PET. In the remaining 3 children for whom only interictal EEG data were available, the PET foci did not correspond in location to the interictal EEG abnormalities. In 11 of the 13 children, the presumed region of seizure onset in the frontal lobe, as based on analysis of seizure semiology, corresponded to the locations of frontal lobe glucose metabolism abnormalities. Conclusions: Although high-resolution PET appears to be very sensitive in localizing frontal lobe glucose metabolic abnormalities in children with intractable FLE and normal CT/ MRI scans, the significance of extrafrontal metabolic disturbances requires further study; these may represent additional epileptogenic areas, effects of diaschisis, seizure propagation sites, or secondary epileptogenic foci.     

Preoperative evaluation for temporal lobe surgery.

Temporal lobe epilepsy (TLE), the most common form of partial epilepsy in adults is often refractory to medical treatment and in these patients epilepsy surgery is considered. Successful surgery is dependent on accurate localisation and lateralisation of the epileptogenic zone. The preoperative evaluation involves a series of assessments and investigations including detailed clinical history, interictal EEG, video-EEG monitoring, MRI, PET, SPECT, and neuropsychology and neuropsychiatric assessment. The role of each of these investigations and assessments in the preoperative evaluation is discussed. Advanced MR techniques including magnetic resonance spectroscopy, MR diffusion and MR perfusion have recently been assessed and are likely to enhance the pre-surgical evaluation of patients with TLE.The surgical outcome and preoperative investigations performed of 80 consecutive patients who underwent temporal lobe surgery between 1993 and 2002 at Royal Melbourne Hospital were reviewed. All patients had MRI, video-EEG monitoring and neuropsychology assessment and 56% a PET scan. During a mean follow-up of 5.9 years 75% had Class 1 outcome, 22% non-Class 1 outcome and 3% were lost to follow-up. The results of preoperative investigations were correlated with outcome. For interictal EEG, seizure semiology, ictal EEG, PET and neuropsychology assessment the surgical outcome of patients in whom results were concordant to side of surgery was compared with those discordant or non-lateralising. There was no significant difference. In 78 of 80 patients MRI revealed mesial temporal sclerosis or a foreign tissue lesion. The outcome was no different between these two groups. Results suggest that in patients with unilateral temporal lobe lesion on MRI and where ictal EEG is either concordant or non-lateralising, other investigations including PET, provide little additional prognostic information.     

Correlation of severity of FDG-PET hypometabolism and interictal regional delta slowing in temporal lobe epilepsy

PURPOSE: We investigated the association of severity of hypometabolism detected by positron emission tomography (PET) with [(18)F]fluorodeoxyglucose (FDG) and persistence of interictal EEG focal slowing in patients with refractory temporal lobe epilepsy. METHODS: Eighty temporal lobes of 40 consecutive patients with intractable temporal lobe epilepsy (mean age, 43.5 years) were studied. All patients underwent video-EEG monitoring, magnetic resonance imaging (MRI), and FDG-PET. Patients with either normal MRI or with unilateral mesial temporal sclerosis, but no other structural abnormality, were included. Interictal EEG delta slowing was graded as none, infrequent (one episode or less/hour), intermediate (more than one episode/hour), or continuous. PET hypometabolism was graded as none, mild, moderate, or severe. RESULTS: The severity of temporal lobe hypometabolism with PET was significantly correlated with the amount of delta activity in the interictal EEG, independent of MRI findings (Spearman r = 0.46; p < 0.0005). CONCLUSIONS: This observation suggests related underlying pathophysiologic mechanisms for metabolic and electrical dysfunction in temporal lobe epilepsy.     

Hypersalivation in temporal lobe epilepsy

PURPOSE: We sought to determine whether hypersalivation helps lateralize seizure onset during complex partial seizures of temporal lobe origin. Several clinical signs, which help lateralize seizure onset, have been reported in temporal lobe epilepsy (TLE). Increased salivation only occasionally has been reported as a manifestation of partial epilepsy. METHODS: Of 590 consecutive patients admitted for video-EEG monitoring, either as a part of a presurgical evaluation of medically intractable epilepsy or for diagnosis and clarification of their paroxysmal symptoms, we identified 10 patients with ictal hypersalivation as a prominent manifestation of complex partial seizures. We reviewed the clinical features, scalp-sphenoidal video-EEG monitoring, intracarotid amytal (Wada) testing, hippocampal volumetric magnetic resonance imaging (MRI), and fluorodeoxyglucose-positron emission tomography (FDG-PET) scans of these patients. RESULTS: Of the 10 patients with ictal hypersalivation, seven patients had nondominant/right TLE, and three patients had dominant/left TLE. All patients had hippocampal atrophy on volumetric MRI. Eight of the 10 patients underwent standard temporal lobectomy with amygdalohippocampectomy (six right, two left). All of the operated-on patients had a seizure-free (Engel class I) outcome, and their increased salivation resolved. Two patients, who did not undergo surgical treatment, continue to have complex partial seizures with increased salivation. CONCLUSIONS: We conclude that increased salivation as a prominent ictal finding in complex partial seizures of temporal lobe origin is more likely to be of nondominant temporal lobe origin. Further studies with larger numbers of patients are needed to replicate this finding.     

An operated case of bitemporal lobe epilepsy associated with old infarction in the left occipital lobe]

A 15-year-old female, who presented with bitemporal lobe epilepsy associated with old infarction in the left occipital lobe, was reported. MRI with fluid attenuated inversion recovery sequence demonstrates cortical atrophy with hyperintensity of the white matter in the left occipital lobe as well as volume loss and hyperintensity of the left hippocampus. Interictal positron emission tomography with [18F]fluorodeoxy glucose (FDG-PET) and single photon emission computed tomography with technetium-99m-ethyl-cysteinate dimer indicate hypometabolism and hypoperfusion in the left occipital lobe and the left temporal lobe, respectively. Scalp recorded EEG did not lateralize the side of the epileptogenic zone. Chronic subdural electrode recording demonstrated that the ictal onset zones were located in the bilateral side of the temporal lobe. Eighty-nine percent of 19 spontaneous seizures were left sided onset. The anterior temporal lobectomy with hippocampectomy was performed for the left side. Although temporal lobe epilepsy is sometimes a bilateral disease, unilateral lobectomy for a strong predominant side, based on the MRI and FDG-PET findings, is effective for some patients.     

Neural correlates of musicogenic epilepsy: SISCOM and FDG-PET

To localize the neural correlates of musicogenic epilepsy, subtraction ictal SPECT coregistered with MRI (SISCOM) and (18)F-fluorodeoxy glucose positron emission tomography (FDG-PET) were performed in a woman who had suffered from frequent musicogenic seizures. She had complex partial seizures consisting of palpitation and an unpleasant feeling, which were followed by staring and oroalimentary automatisms. Ictal EEG showed rhythmic theta waves originated from the right temporal lobe, and SISCOM showed ictal hyperperfusion on right insula, amygdala, hippocampal head, and anterior temporal lobe, whereas interictal FDG-PET showed interictal hypometabolism in the same brain regions, suggesting dysfunction and abnormal activation of right temporo-limbic structures related to an emotional response to music.     

Is 11C-flumazenil PET superior to 18FDG PET and 123I-iomazenil SPECT in presurgical evaluation of temporal lobe epilepsy?

OBJECTIVE: To determine the contribution of 18FDG PET, 11C-flumazenil PET, and 123I-iomazenil SPECT to the presurgical evaluation of patients with medically intractable complex partial seizures. METHODS: Presurgical evaluation was performed in 23 patients, who were considered candidates for temporal lobe resective surgery (14 females and nine males with a median age of 34 (range 13 to 50) years). The presurgical diagnosis was based on seizure semiology as demonstrated with ictal video recording, ictal and interictal scalp EEG recordings, and MRI. RESULTS: Eighteen patients had convergent findings in clinical semiology, interictal and ictal EEG with scalp and sphenoidal electrodes, and MRI that warranted surgery without depth EEG (DEEG). In five patients with insufficient precision of localisation, DEEG with intracerebral and subdural electrodes was performed. MRI showed abnormalities in 22 out of 23 patients. Of these 22, 18 had mesial temporal sclerosis. This was limited to the mesial temporal lobe in four and more widespread in the temporal lobe in 14 patients. In one patient only enlargement of the temporal horn was found and in three others only white matter lesions were detected. 18FDG PET showed a large area of glucose hypometabolism in the epileptogenic temporal lobe, with an extension outside the temporal lobe in 10 of 23 patients. Only in one of these patients DEEG showed extratemporal abnormalities that were concordant with a significant extratemporal extension of hypometabolism in 18FDG PET. 18FDG PET was compared with the results of scalp EEG: in none of the patients was an anterior temporal ictal onset in scalp EEG related to a maximum hypometabolism in the mesial temporal area. By contrast, the region of abnormality indicated by 11C-flumazenil PET was much more restricted, also when compared with DEEG findings. Extension of abnormality outside the lobe of surgery was seen in only two patients with 11C-flumazenil and was less pronounced compared with the intratemporal abnormality. Both 18FDG PET and 11C-flumazenil PET reliably indicated the epileptogenic temporal lobe. Thus these techniques provide valuable support for the presurgical diagnosis, especially in patients with non-lesional MRI or non-lateralising or localising scalp EEG recordings. In those patients in whom phase 1 presurgical evaluation on the basis of classic methods does not allow a localisation of the epileptogenic area, PET studies may provide valuable information for the strategy of the implantation of intracranial electrodes for DEEG. Previous studies have suggested that 11C-flumazenil binding has a closer spatial relationship with the zone of ictal onset than the area of glucose hypometabolism, but this study suggests rather that the decrease in the 11C-flumazenil binding simply reflects a loss of neurons expressing the benzodiazepine-GABA receptor. 11C-flumazenil PET did not prove to be superior to 18FDG PET. CONCLUSION: In 21 patients sufficient material was obtained at surgery for a pathological examination. In 17 mesial temporal sclerosis, in one an oligodendroglioma grade B, in another a vascular malformation and in two patients no abnormalities were found. Although all 21 patients with pathological abnormality showed hypometabolic zones with 18FDG PET and a decreased uptake in 11C-flumazenil binding, there was no strong correlation between pathological diagnosis and functional abnormal areas in PET. Grading of medial temporal sclerosis according to the Wyler criteria showed no correlation with the degree of hypometabolism in either 18FDG or 11C-flumazenil PET. The interictal 123I-iomazenil SPECT technique was highly inaccurate in localising the lobe of surgery.     

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.