Magnetic resonance imaging and temporal lobe epilepsy

Surgical treatment is a well established option for patients with medically refractory temporal lobe epilepsy. Magnetic resonance imaging (MRI) has revolutionized the evaluation of these patients. New techniques can identify structural, metabolic and functional abnormalities associated with the epileptogenic zone. Mesial temporal sclerosis is the most common pathological finding and presents as hippocampal atrophy, which can be detected by visual inspection in most cases. Volumetric analysis of medial temporal structures offers the advantage of detecting bilateral abnormalities. Magnetic resonance spectroscopy can detect metabolic abnormalities associated with the epileptogenic focus. Functional MRI allows for the non-invasive evaluation of cognitive function, allowing for the localization of the neuroanatomic substrate of motor, sensory and cognitive functions. Intraoperative MRI-based image guided systems are a useful adjunct in the surgical treatment of this epileptic syndrome.     

MRI与PET在颞叶癫癎中定位价值的比较

目的 比较ＭＲＩ及ＦＤＧ－ＰＥＴ在颞叶癫癎致癎灶定位中的价值,探讨癫癎外科术前定位的方法以及手术预后的判断。方法 以手术后癫癎控制状况为标准,对３０例颞叶癫癎患者的术前ＭＲＩ和ＦＤＧ－ＰＥＴ的结果进行比较,分析ＭＲＩ及ＰＥＴ各自在癫癎致癎灶定位中的价值。结果ＭＲＩ有良好的脑结构分辨能力,对于症状性癫癎的定位价值高,当ＭＲＩ显示海马硬化时,对致癎灶定位的意义大,术后癫癎发作完全控制的可能性大。发作间期ＰＥＴ对于颞叶癫癎定位的敏感性高于ＭＲＩ,但ＰＥＴ低代谢的范围往往超过致癎灶。与ＰＥＴ的目测方法比较,ＰＥＴ半定量分析并不能提高致癎灶定位的准确性及对手术效果的预测。结论　ＭＲＩ与ＰＥＴ检查结合可以提高致癎灶定位的准确性及对手术效果的预测,减少颅内记录的应用。     

Image guided audit of surgery for temporal lobe epilepsy.

Studies on surgery for temporal lobe epilepsy are hampered by lack of information about the actual surgery that has taken place. A method is described for accurately measuring the volumes of resection by MRI after surgery. Ten cases of surgically treated temporal lobe epilepsy (nine non-tailored resections, one selective amygdalohippocampectomy) are presented to show the technique. Indices of extent of resection in both the mesiobasal and lateral temporal lobe compartments have been measured, compared, and evaluated. By comparison with identical preoperative volumetric MRI the hippocampal resections have been correlated with the demonstrated hippocampal volume loss, thought to be of relevance in the aetiology of temporal lobe epilepsy. Detailed postoperative audit in this manner is vital in providing a rational basis for follow up studies of outcome.     

Quantitative magnetic resonance imaging of the amygdala in temporal lobe epilepsy-clinico-pathological correlations (a pilot study)

PURPOSE: We carried out a pilot study of quantitative volumetric MRI of the amygdala in patients undergoing surgery for intractable temporal lobe epilepsy. We wished to explore whether amygdala volume correlated with pre-operative clinical variables and post-operative outcome.METHODS: Ten patients had detailed volumetric measurements of their amygdala and hippocampus according to operationalised anatomical criteria from an optimised MRI imaging sequence. A ratio of volumes from the unoperated to operated side was calculated. Surgical specimens were examined histologically for astrocytosis.RESULTS: The volumes of the amygdala and hippocampus on the operated side were significantly smaller than on the unoperated side. More severe astrocytosis appeared to go along with smaller volume ratios but the relationship was not significant. There were few significant correlations between volumes measures and clinical or outcome variables.CONCLUSION: Reductions in amygdala volume in the to-be-operated temporal lobe in patients with medically intractable epilepsy can be reliably detected using volumetric MRI. Accurate amygdala volume measures do not appear to exert a significant effect on clinical presentation and outcome in the presence of hippocampal volumes reductions, but may be useful in confirming bilateral pathology. Larger studies examining clinico-pathological correlations are recommended.     

Epilepsy surgery

Only 15% of patients with severe epilepsy with frequent partial seizures achieve any improvement in their seizure frequency by further drug treatment. As we know that epileptic seizures result in neuron loss with early development of mental deterioration, that the mortality rate of patients with epilepsy is increased and that an exact localization of the epileptogenic area which can be resected offers the possibility of curative treatment, we have a moral obligation to make this treatment available to people disabled with epilepsy. Surgery for mesial temporal sclerosis and lesional cortical partial epilepsy offers freedom from seizures in 70–80% of the patients, whereas non-lesional, cortical, partial epilepsy is more problematic, as only 30–40% of the patients will be seizure-free. Volumetric MRI, MR spectroscopy, SPECT and PET reduce the need for invasive monitoring in patients with temporal lobe epilepsy. Invasive recordings should be used when scalp-EEG, MRI, SPECT and PET cannot identify the epileptic focus; 50% of the patients who cannot be diagnosed by non-invasive recordings, can be diagnosed by invasive methods. When operated on 70% become seizure free, and a further 10% achieve a significant improvement. As age at surgery influences vocational outcome, surgical therapy should be considered in children. This will prevent their development into chronically ill patients, with all the known accompanying psychic handicaps this involves.     

Parahippocampal epilepsy with subtle dysplasia: A cause of “imaging negative” partial epilepsy

Purpose: Lesion‐negative refractory partial epilepsy is a major challenge in the assessment of patients for potential surgery. Finding a potential epileptogenic lesion simplifies assessment and is associated with good outcome. Here we describe imaging features of subtle parahippocampal dysplasia in five cases that were initially assessed as having imaging‐negative frontal or temporal lobe epilepsy. Methods: We analyzed the clinical and imaging features of five patients with seizures from the parahippocampal region. Results: Five patients had subtle but distinctive magnetic resonance imaging (MRI) abnormalities in the parahippocampal gyrus. This was a unilateral signal abnormality in the parahippocampal white matter extending into gray matter on heavily T₁‐ and T₂‐weighted images with relative preservation of the gray–white matter boundary on T₁‐weighted volume sequences. Only one of these patients had typical electroclinical unilateral temporal lobe epilepsy (TLE); one mimicked frontal lobe epilepsy, two showed bitemporal seizures, and one had unlocalized partial seizures. All have had surgery; four are seizure‐free (one has occasional auras only, follow‐up 6 months to 10 years), and one has a >50% seizure reduction. Histopathologic evaluation suggested dysplastic features in the surgical specimens in all. Discussion: In patients with lesion‐negative partial epilepsy with frontal or temporal semiology, or in cases with apparent bitemporal seizures, subtle parahippocampal abnormalities should be carefully excluded. Recognizing the MRI findings of an abnormal parahippocampal gyrus can lead to successful surgery without invasive monitoring, despite apparently incongruent electroclinical features.     

New methods for evaluation of memory in temporal lobe epilepsy: a functional imaging approach]

Temporal lobe epilepsy (TLE) is usually associated with a specific impairment of memory functions. A reliable assessment of memory function seems therefore a crucial element of the presurgical evaluation for surgery epilepsy, especially for temporal lobectomy. To date, intracarotid amobarbital testing remains the gold standard to evaluate memory before planning surgery in patients with refractory TLE. Functional imaging, either positron emission tomography or functional MRI, holds great promise as a powerful tool in memory evaluation. Preliminary studies, essentially in healthy volunteers, have shown promising results. In the future, functional imaging, combined with other techniques, will certainly contribute to the clinical presurgical evaluation of patients with epilepsy.     

Bilateral Hippocampal Volume Loss in Patients with a History of Encephalitis or Meningitis

Volumetric analysis of high-quality magnetic resonance imaging (MRI) scans identifies asymmetric hippocampal atrophy in most patients with temporal lobe epilepsy. However, bilateral hippocampal atrophy can be missed by unnormalized volume measures. We considered two patient groups with temporal lobe epilepsy, one with a history of febrile convulsions (FC, n = 14) and one with a history of encephalitis or meningitis (E/M, n = 12), to compare the prevalence of bilateral volume loss between the groups. A volume normalization process defines a normal range of hippocampal volumes in control subjects (n = 32). Normalized volumes indicated that 11 of 14 subjects with a history of FC had unilateral hippocampal atrophy and 9 of 12 subjects with a history of E/M had bilateral hippocampal atrophy as compared with the controls. Visual assessments of unilateral hippocampal atrophy (n = 17) correlated well with measured unilateral volume loss (n = 14), but visual assessment of bilateral hippocampal atrophy (n = 3) correlated poorly with measured bilateral volume loss (n = 12). Mean age at seizure onset was lower in the FC group (7 years) than in the E/M group (13 years), but other clinical features were similar between the two groups. Hippocampal volume normalization is necessary to detect bilateral volume loss, which is common in patients with a history of encephalitis or meningitis.     

Predictors of outcome after temporal lobectomy for refractory temporal lobe epilepsy

Objective – To identify predictors of outcome after epilepsy surgery in patients with temporal lobe epilepsy (TLE). Methods – Seventy‐six patients with normal magnetic resonance imaging (MRI) or hippocampal sclerosis on MRI who underwent anterior temporal lobe resections were included. Outcome 2 years after surgery was classified as good (Engel I and II) or poor (Engel III and IV). Gender, age at onset and duration of epilepsy, history of febrile convulsions, auras, right‐ or left‐sided TLE, memory ipsilateral to seizure onset (Wada test), hippocampal asymmetry (HA) and T2 relaxation time, amygdala, temporal lobe and hemispheral volume were tested for associations with outcome. Results – Sixty‐seven percent had a good outcome. Of all parameters tested, only a history of febrile convulsions and HA on quantitative MRI were significantly associated with a good seizure outcome. The absence of these parameters did not exclude a good outcome, but only five of 18 patients (28%) without HA and without a history of febrile convulsions had a good outcome. Conclusion – Febrile convulsions and HA were predictors of outcome after epilepsy surgery in TLE. Subtle volume loss in amygdala, temporal lobe or hemispheres and the memory ipsilateral to the side of resection were not associated with outcome.     

Epilepsiechirurgie

Epilepsy surgery is an important therapeutic option for patients with epilepsy since one third of all epilepsy patients will still not be become seizure free despite newly developed antiepileptic drugs. Anterior temporal lobe resection is the most common procedure. Extratemporal resections require more complex diagnostics and often invasive evaluation which is not the case in most temporal epilepsy patients due to improved imaging (MRI, PET, SPECT). Electrical stimulation of the anterior thalamus has been available as a treatment option since last year.     

The amygdala and sexual drive: insights from temporal lobe epilepsy surgery

The aim of this study was to explore the relationship between the amygdala and human sex drive. We compared amygdalar volume in groups of patients with or without sexual changes after temporal lobe resection and in age-matched neurologically normal subjects. Forty-five patients with intractable temporal lobe epilepsy who underwent surgical resection in the Comprehensive Epilepsy Program at the Austin and Repatriation Medical Centre completed a semistructured interview and questionnaire relating to sexual outcome after surgery. Volumetric analyses of both amygdalae were conducted on the patients' preoperative T(1)-weighted magnetic resonance imaging scans and those of 46 neurologically normal controls. Patients who reported a postoperative sexual increase had a significantly larger amygdalar volume contralateral to the site of their resective surgery than patients with a sexual decrease or no change than control subjects. There was a significant positive relationship between contralateral amygdalar volume and the maximum degree of sexual change. We have demonstrated a relationship between contralateral amygdalar volume and sexual outcome in patients undergoing temporal lobe resection. This finding provides evidence for an important role of the amygdala in regulating human sexual behavior. A larger contralateral amygdala may contribute to the expression of increased or improved sexuality after temporal lobe resection.     

Endovascular ablation of a temporal lobe epileptogenic focus - a complication of Wada testing

The authors report on a patient with a long history of medically refractory temporal lobe epilepsy. During pre-operative evaluation for anterior temporal lobectomy he underwent a Wada test for speech and memory lateralization. During the procedure, he suffered a focal cerebral infarct, within the right medial temporal lobe, at the site of the epileptic focus. This resulted in the resolution of his seizure disorder. The possibility of endovascular management of seizure disorders of the temporal lobe should be investigated further as a potentially minimal invasive therapeutic option for medically intractable epilepsy.     

Commentary: How Has Neuroimaging Improved Patient Care?

Summary: Neuroimaging has significantly altered the management of patients with partial epilepsy. Magnetic resonance imaging (MRI) has been demonstrated to be a reliable and accurate indicator of the common pathologic findings underlying a partial seizure disorder. Intracranial mass lesions have been shown to be highly coherent with the localization of the epileptogenic zone. An MRI-identified epileptogenic lesion affects the selection of patients for epilepsy surgery and alters the diagnostic evaluation and the operative strategy. The results of the MRI preoperatively have prognostic importance in patients undergoing surgical treatment for partial epilepsy. Patients with lesional epileptic syndromes are considered favorable candidates for surgical ablative treatment. Hippo-campal volume studies may predict the neurocognitive outcome in patients undergoing temporal lobe surgery. The use of MRI has resulted in a reduction in chronic intracranial EEG monitoring at most epilepsy centers, especially in patients with lesional pathology. MRI may be a reasonable initial "screening" procedure in selected patients with intractable partial epilepsy before consideration of a presurgical evaluation. A classification of partial epilepsy is proposed, based on the results of MRI, that may be useful for patients being considered for surgical treatment. Importantly, preoperative MRI must be correlated with the electrophysiologic studies and ictal semiology before decision-making regarding surgical therapy.     

Temporal Lobe Epilepsy: When Are Invasive Recordings Needed?

Temporal lobe epilepsy (TLE) is the most common type of medically intractable partial epilepsy amenable to surgery. In the majority of cases, the underlying pathology in temporal lobe epilepsy is mesial temporal sclerosis (MTS). Whereas historically invasive recordings were required for most epilepsy surgeries, indications have dramatically changed since the introduction of high-resolution MRI, which uncovers structural lesions in a high percentage of cases. No invasive recordings are required to perform a temporal lobectomy in patients with intractable epilepsy who have structural imaging suggesting unilateral MTS and concordant interictal and ictal surface EEG recordings, functional imaging, and clinical findings. Invasive testing is needed if there is evidence of bitemporal MTS on structural imaging and/or electrophysiologically, and additional information from functional imaging, neuropsychology, and the intracarotid amobarbital (Wada) test also does not help to lateralize the epileptogenic zone. Depth electrodes can be particularly helpful in this setting. However, no surgery is indicated, even without invasive recordings, if bitemporal-independent seizures are recorded by surface EEG and all additional testing is inconclusive. Other etiologies of TLE such as a tumor, vascular malformation, encephalomalacia, or congenital developmental abnormality account for about 30% of all patients who undergo epilepsy surgery. Epilepsy surgery is indicated after limited electrophysiologic investigations if neuroimaging and electrophysiology converge. However, approaches for resection in lesional temporal lobe epilepsy vary among centers. Completeness of resection is crucial and invasive recordings may be needed to guide the resection by mapping eloquent cortex and/or to determine the extent of the non-MRI-visible epileptogenic area. Specific approaches for the different pathologies are discussed because there is evidence that the relationship between the lesions visible on MRI and the epileptogenic zone varies among lesions of different pathologies, and therefore variable surgical strategies must be applied.     

Temporal pole epilepsy surgery—Sparing the hippocampus

Temporal pole epilepsy (TPE) is a poorly known and difficult to individualize subtype of temporal lobe epilepsy. Consequently, in drug-resistant TPE, there is still a debate on the need for a large surgical removal of the temporal pole and mesial temporal structures or a limited resection of the temporal pole. We reviewed all patients who underwent presurgical evaluation for drug-resistant epilepsy over a 17-year period, and report here 19 patients with proven drug-resistant temporal pole epilepsy who underwent a selective temporal pole resection with respect to mesial structures. Most (15) TPE patients exhibited seizures resembling mesiotemporal seizures, whereas the others exhibited nocturnal hyperkinetic seizures or an association of both seizure types. MRI revealed a temporal pole lesion in 58% of patients. Long-term postoperative outcome after a conservative surgery was excellent: 63% of patients were seizure-free (International League Against Epilepsy [ILAE] 1) at 1-year postsurgery and 78% at 5 years. These results show that TPE has no specific electroclinical features but is a distinct type of temporal lobe epilepsy allowing a conservative surgery. Respecting the mesiotemporal structures is a valid surgical approach for drug-resistant temporal pole epilepsy.     

Ipsilateral and contralateral MRI volumetric abnormalities in chronic unilateral temporal lobe epilepsy and their clinical correlates

PURPOSE: To assess the presence, extent, and clinical correlates of quantitative MR volumetric abnormalities in ipsilateral and contralateral hippocampus, and temporal and extratemporal lobe regions in unilateral temporal lobe epilepsy (TLE). METHODS: In total, 34 subjects with unilateral left (n = 15) or right (n = 19) TLE were compared with 65 healthy controls. Regions of interest included the ipsilateral and contralateral hippocampus as well as temporal, frontal, parietal, and occipital lobe gray and white matter. Clinical markers of neurodevelopmental insult (initial precipitating insult, early age of recurrent seizures) and chronicity of epilepsy (epilepsy duration, estimated number of lifetime generalized seizures) were related to magnetic resonance (MR) volume abnormalities. RESULTS: Quantitative MR abnormalities extend beyond the ipsilateral hippocampus and temporal lobe with extratemporal (frontal and parietal lobe) reductions in cerebral white matter, especially ipsilateral but also contralateral to the side of seizure onset. Volumetric abnormalities in ipsilateral hippocampus and bilateral cerebral white matter are associated with factors related to both the onset and the chronicity of the patients' epilepsy. CONCLUSIONS: These cross-sectional findings support the view that volumetric abnormalities in chronic TLE are associated with a combination of neurodevelopmental and progressive effects, characterized by a prominent disruption in ipsilateral hippocampus and neural connectivity (i.e., white matter volume loss) that extends beyond the temporal lobe, affecting both ipsilateral and contralateral hemispheres.     

SECTION D: NEUROSURGERY & NEUROPATHOLOGY

Comparison of surgical and medical treatment for partial epilepsy. Medical and social implications of the treatment
Procedures in Pediatric Epilepsy Surgery
The possible need for intra-cranial EEG in surgery for temporal lobe epilepsy
Consistency of lateralisation in intracranial record-ings of seizures of temporal lobe origin
Comparison of lateralising capability of 99Tc^m HM-PAO-SPECT, neuropsychology, interictal and ictal EEG in the pre-surgical evaluation of patients with intractable epilepsy
Convergence of CT/MRI, "FDG-PET, intracarotid amobarbital procedure and D.EEG in presurgical evaluation of refractory partial epilepsy
Surgery for epilepsy in the United Kingdom
Anterior 2/3 callosotomy for the treatment of in-tractable epilepsy
Pre-surgical EEG evaluation
A simplified technique for epidural recording of epi-leptiform activity and seizure patterns
Discrepancy between interictal and ictal EEG-find-ings - the use of subdural electrodes may solve the problem
Temporal mesiolimbic versus temporal neocortical complex partial seizures; electroclinical correlates recorded by combined depth and subdural electrodes
Verifying electrical dipole localization in patients with epilepsy undergoing depth EEG recordings in the presurgical evaluation of intractable epilepsy
A current dipole tracing method locating interictal epileptiform activity in patients with focal epilepsy
PET-studies on distribution of glia in patients with focal epilepsy
Relationship of pre-operative neuropsychological test to the sodium amytal test - results on an empiri-cal study
Amygdalohippocampectomy in complex partial epi-lepsy     

The clinical spectrum of focal cortical dysplasia and epilepsy

Focal cortical dysplasia is an important pathologic substrate in patients with epilepsy, but its clinical spectrum has not yet been completely defined. We retrospectively studied 30 epilepsy surgery patients with focal abnormalities of neuronal migration as the only histopathologic finding in resected tissue. Patients comprised two clinical groups. Seventeen patients with extratemporal epilepsy had early (median age, 7.0 years) extratemporal resection or hemispherectomy for severe epilepsy (47% of patients with > 10 partial seizures a day) that began in infancy or early childhood (median age, 1.0 year), usually in the setting of mental retardation or developmental delay (59% of patients), and often with magnetic resonance imaging (MRI) evidence of focal neuronal migration abnormality (44% of patients). In contrast, 13 patients with temporal lobe epilepsy were significantly older at age of seizure onset (median, 8.0 years; p = 0.001) and surgery (median, 22.0 years; p = 0.001), with less severe epilepsy (no patients with an average of > 10 seizures a day; p = 0.004), and without mental retardation or MRI evidence of neuronal migration abnormality (p = 0.001). In both groups, positron emission tomography (PET) was more sensitive than MRI and showed focal hypometabolism in seven patients with normal MRI. Seizure-free outcome tended to be more common after temporal lobectomy (77%) than after extratemporal resection or hemispherectomy (53%). Pathologic abnormalities were more severe in patients with extratemporal epilepsy than in patients with temporal lobe epilepsy. The clinical spectrum of focal cortical dysplasia included not only infants and children with severe extratemporal epilepsy and mental retardation, but also older patients with temporal lobe epilepsy and at least boderline IQ. Preoperative diagnosis may be difficult in cases with less severe pathologic abnormality, but high-resolution MRI and PET can increase the yield.     

Outcome after surgery in patients with refractory temporal lobe epilepsy and normal MRI.

Our purpose is to determine predictors of outcome in patients with refractory temporal lobe epilepsy and normal high resolution magnetic resonance imaging (MRI) who undergo surgical therapy. We identified 23 patients who underwent temporal lobectomy and had normal pre-operative MRI, including surface coil phased array temporal lobe imaging. All were followed at least 2 years after surgery. We graded outcome as seizure-free, > 75% reduction in seizures, or < 75% reduction in seizures. We examined pre-operative interictal and ictal electroencephalographic (EEG) findings, age of onset, gender, duration of epilepsy, risk factors, family history, physical findings, age at operation, side of operation, and pathology of resected tissue in order to determine if any of these factors were associated with outcome. Overall, 48% (11/23) of patients were seizure-free, 39% (9/23) had > 75% reduction in seizures, while 13% (3/23) had < 75% reduction in seizures. Only the EEG findings were useful in predicting outcome. When ictal onsets arose from basal-temporal regions, 61% (11/18) of patients were seizure-free, while none (0/5) were seizure-free when seizures arose from mid-posterior temporal regions (P = 0.04). Interictally, if all epileptiform patterns were localized exclusively to one basal-temporal region, a finding that invariably correlated with ictal onsets, 78% (7/9) of patients were seizure-free, while only 29% (4/14) were seizure-free if discharges were bilateral or multifocal (P = 0.04). We conclude that surgery may be a reasonable treatment for some patients with intractable temporal lobe seizures and normal MRI. The best outcomes occur when seizure onsets and interictal epileptiform patterns are exclusive to one basal-temporal region. Unfavorable outcomes are most likely to occur when ictal origins are from mid-posterior temporal regions and when interictal discharges are bitemporal or multifocal in distribution.     

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.