Parenchymal lesions in pharmacoresistant temporal lobe epilepsy: dual and multiple pathology

Evaluation of dual pathology among drug-resistant epileptic patients with hippocampal sclerosis

PURPOSE

Dual pathology (DP) is defined as simultaneous presence of hippocampal sclerosis (HS) and any other pathology in the brain. Since this is a less probed concept, we aimed to evaluate the frequency and characteristics of DP among drug-resistant epileptic patients with HS.

METHODS

This is a cross-sectional study conducted during 2007-2016 in Kashani Comprehensive Epilepsy Center, Isfahan, Iran. Patients with diagnosis of drug-resistant epilepsy and HS were enrolled in the study, and demographic data, seizure semiology, EEG findings, and MRI findings were collected. We compared these variables between three groups of DP, unilateral HS, and bilateral HS.

RESULTS

Of the 200 enrolled cases, 29 patients (14.5%) had DP and 21 patients (10.5%) had bilateral HS; the remaining patients had unilateral HS. The average age of patients with DP was 30.03, and 65.5% of them were male. Patients with DP had more EEG discharges from regional and multi-focal sites compared to unilateral HS (P value < 0.001). Also, complex partial seizure (CPS) was more commonly presented in patients with unilateral HS (96.8%). Comparison of disease characteristics between DP and bilateral HS showed no difference in most categories (P > 0.05).

CONCLUSIONS

We found DP among 14.5% of our drug-resistant epileptic patients with HS. DP patients mostly presented with CPS and had high proportion of ictal and interictal EEG discharges from regional and multi-focal areas. Gliosis and focal cortical dysplasia were the most common pathologies among DP patients. Patients with DP showed a similar behavior to bilateral HS in many features.

Surgical strategy for temporal lobe epilepsy with dual pathology and incomplete evidence from EEG and neuroimaging

Coexistence of hippocampal sclerosis (HS) and a temporal neocortical lesion, including focal cortical dysplasia, vascular malformations or benign primary brain tumors, is defined as dual pathology. In the majority of cases, the complete evidence based on electroencephalogram (EEG) and magnetic resonance imaging (MRI) for each of the dual pathological lesions is difficult to obtain. As a result, patients with dual pathology are poor surgical candidates due to potential incomplete resection of the epileptogenic zone. The current study retrospectively reviewed 24 patients with potential dual pathology and incomplete EEG and MRI evidence, aiming to provide novel surgical strategies. The results revealed a significantly worse seizure-free outcome for patients with incomplete EEG and MRI data compared with patients who received a clear diagnosis of dual pathology based on complete test results (11.1 vs. 60.0%; P<0.05). Notably, satisfying surgical (seizure-free) outcomes were still achieved in 60% of patients with unclear EEGs to locate the onset zone and clear MRI scans identifying the sclerotic hippocampus and nearby neocortical lesions, which could be resected together. In patients with multiple epileptogenic onsets or with widespread epileptic discharges, the hippocampus should be spared from resection due to concern for potential postsurgical mood or memory disorders. In conclusion, patients with resection of the sclerotic hippocampus and neocortical lesion had improved seizure-free outcomes compared with patients who received individual lesion resection. The current study aimed to provide a novel surgical strategy for neurosurgeons treating epileptic patients with dual pathology.

White matter in temporal lobe epilepsy: clinico-pathological correlates of water diffusion abnormalities

Using magnetic resonance imaging, it is possible to measure the behavior of diffusing water molecules, and the metrics derived can be used as indirect markers of tissue micro-architectural properties. Numerous reports have demonstrated that patients with temporal lobe epilepsy (TLE) have water diffusion abnormalities in several white matter structures located within and beyond the epileptogenic temporal lobe, showing that TLE is not a focal disorder, but rather a brain network disease. Differences in severity and spatial extent between patients with or without mesial temporal sclerosis (MTS), as well as differences related to hemispheric seizure onset, are suggestive of different pathophysiological mechanisms behind different forms of TLE, which in turn result in specific cognitive disabilities. The biological interpretation of diffusion abnormalities is based on a wealth of information from animal models of white matter damage, and is supported by recent reports that directly correlate diffusion metrics with histological characteristics of surgical specimens of TLE patients. Thus, there is now more evidence showing that the increased mean diffusivity (MD) and concomitant reductions of diffusion anisotropy that are frequently observed in several white matter bundles in TLE patients reflect reduced axonal density (increased extra-axonal space) due to smaller-caliber axons, and abnormalities in the myelin sheaths of the remaining axons. Whether these histological and diffusion features are a predisposing factor for epilepsy or secondary to seizures is still uncertain; some reports suggest the latter. This article summarizes recent findings in this field and provides a synopsis of the histological features seen most frequently in post-surgical specimens of TLE patients in an effort to aid the interpretation of white matter diffusion abnormalities.

The surgical management of pediatric brain tumors causing epilepsy: consideration of the epileptogenic zone

OBJECTIVE

Children suffering from epilepsy with suspected low-grade tumors may benefit from a surgical approach that considers the epileptogenic zone, which can be more extensive than the tumor region. This study aimed to determine the prevalence of epilepsy in children undergoing supratentorial tumor resection and the factors predictive of postoperative seizure freedom in children with low-grade tumors.

METHODS

Subjects 3 months to 21 years undergoing supratentorial brain tumor resection between 2007 and 2011 were included in this retrospective study. Children with supratentorial, cortically based tumors and a preoperative diagnosis of epilepsy were considered epilepsy surgery candidates. Pre- and postoperative MRI were reviewed and scored for extent of resection, adjacent dysplasia, and remaining abnormal cortex postoperatively.

RESULTS

The prevalence of seizures in all cases of supratentorial tumors was 46/87 (53 %). Eighteen were epilepsy surgery candidates. Eight of 18 (44 %) were seizure-free postoperatively with a mean follow-up of 39 months. Children who were seizure free postoperatively had tried fewer anticonvulsants than those with continued seizures (1.7 v. 2.9, p = 0.01). Presurgical evaluation was nonstandardized, and a more extensive workup and resection were performed in children who continued to have seizures postoperatively.

CONCLUSIONS

All epilepsy surgery candidates had low-grade tumors on histological evaluation, indicating that a surgical approach that takes into consideration the epileptogenic zone is reasonable in this population. Gross total resection should be the goal, with additional attention to resection of the epileptogenic zone when located in the noneloquent cortex.

3 TESLA MR imaging in adults with focal onset epilepsy

OBJECTIVE

The finding of cerebral epileptogenic lesions in magnetic resonance (MR) has demonstrated to be a relevant prognostic factor for potential surgical candidates. In a series of consecutive adults with focal onset epilepsy, we investigated the yield of 3T MR imaging for detecting epileptogenic cerebral lesions.

MATERIALS AND METHODS

We prospectively recruited 161 adult patients with a diagnosis of focal epilepsy, all of whom underwent standardized MR imaging study performed with a 3T magnet.

RESULTS

Lesion-related epilepsy was observed in 48% of patients, and 12% of cryptogenic patients showed subtle or non-specific lesions related to the epileptogenic source. The most common findings were focal cortical dysplasia and vascular lesions, followed by mesial temporal sclerosis, tumors, and scars from previous cerebral injuries. Patients older than 72 years were more likely to have vascular epilepsy.

CONCLUSIONS

Diagnostic assessment using a standardized 3T MR imaging protocol for focal-onset epilepsy detects lesions in nearly half the patients. Our results indicate that elders with focal epilepsy should be searched for vascular lesions.

Surgical and postmortem pathology studies: contribution for the investigation of temporal lobe epilepsy

Pathology studies in epilepsy patients bring useful information for comprehending the physiopathology of various forms of epilepsy, as well as aspects related to response to treatment and long-term prognosis. These studies are usually restricted to surgical specimens obtained from patients with refractory focal epilepsies. Therefore, most of them pertain to temporal lobe epilepsy (TLE) with mesial temporal sclerosis (MTS) and malformations of cortical development (MCD), thus providing information of a selected group of patients and restricted regions of the brain. Postmortem whole brain studies are rarely performed in epilepsy patients, however they may provide extensive information on brain pathology, allowing the analysis of areas beyond the putative epileptogenic zone. In this article, we reviewed pathology studies performed in epilepsy patients with emphasis on neuropathological findings in TLE with MTS and MCD. Furthermore, we reviewed data from postmortem studies and discussed the importance of performing these studies in epilepsy populations.

Epilepsy surgery of the temporal lobe in pediatric population: a retrospective analysis

BACKGROUND

There is still some reluctance to refer pediatric patients for epilepsy surgery, despite evidence of success in retrospective series.

OBJECTIVE

To describe surgical experience and long-term outcome in pediatric temporal lobe epilepsy (TLE) at a single institution.

METHODS

Retrospective review of pediatric (<18-years-old) TLE patients who underwent surgery between November 1996 and December 2006 at Cleveland Clinic Epilepsy Center. Cox proportional hazard modeling was used to assess outcome predictors.

RESULTS

One hundred thirty pediatric patients met study criteria. Mean time between seizure onset and surgery was 6.3 years. Invasive evaluation was used in 32 patients (24.5%). Hippocampal sclerosis was present in 70 patients (53.8%), either alone or associated in dual pathology. The complication rate was 7%. The seizure-freedom rates at 1, 2, 5, and 12 years were 76%, 72%, 54%, and 41%, respectively (Kaplan-Meier). With the use of the Engel outcome classification, 98 (75.3%) patients were class I, 11 (8.5%) class II, 9 (7%) class III, and 12 (9.2%) were class IV at last follow-up. Only 4 (3.1%) patients underwent reoperations. Antiepileptic drugs (AEDs) were discontinued in 36 patients (28.3%) in a mean period of 18 months (SD ± 17 months; range, 6-102 months). Although left-sided resection, lower number of preoperative AED trials (≤ 4), and tumor pathology correlated with favorable seizure outcomes, extensive surgical resection remained the only significant outcome predictor after multivariate analysis (P = .007; HR = 0.13 [95% confidence interval 0.007-0.64]).

CONCLUSION

Careful selection of surgical candidates by multidisciplinary evaluations is required. Long-term seizure control is achieved successfully with acceptable low complication rates.

Temporal lobe epilepsy surgery failures: a review

Patients with temporal lobe epilepsy (TLE) are refractory to antiepileptic drugs in about 30% of cases. Surgical treatment has been shown to be beneficial for the selected patients but fails to provide a seizure-free outcome in 20–30% of TLE patients. Several reasons have been identified to explain these surgical failures. This paper will address the five most common causes of TLE surgery failure (a) insufficient resection of epileptogenic mesial temporal structures, (b) relapse on the contralateral mesial temporal lobe, (c) lateral temporal neocortical epilepsy, (d) coexistence of mesial temporal sclerosis and a neocortical lesion (dual pathology); and (e) extratemporal lobe epilepsy mimicking TLE or temporal plus epilepsy. Persistence of epileptogenic mesial structures in the posterior temporal region and failure to distinguish mesial and lateral temporal epilepsy are possible causes of seizure persistence after TLE surgery. In cases of dual pathology, failure to identify a subtle mesial temporal sclerosis or regions of cortical microdysgenesis is a likely explanation for some surgical failures. Extratemporal epilepsy syndromes masquerading as or coexistent with TLE result in incomplete resection of the epileptogenic zone and seizure relapse after surgery. In particular, the insula may be an important cause of surgical failure in patients with TLE.

Clinical features and pathological characteristics of amygdala enlargement in mesial temporal lobe epilepsy

Although the hippocampus is considered an important site of seizures in mesial temporal lobe epilepsy (mTLE), the amygdala may also have a significant role. Amygdala enlargement is occasionally found in patients with mTLE, and volumetric detection of amygdala enlargement has been documented in "image-negative" patients with TLE. However, only limited data have been reported on the clinical features, surgical outcomes, and pathological characteristics in patients with mTLE with amygdala enlargement. We recruited 12 patients who had undergone surgical treatment for refractory epilepsy with radiological evidence of amygdala enlargement, and 11 became seizure free. All patients showed homogenously increased amygdala volumes on MRI without enhancement and underwent surgical treatment for mTLE. Pathology results revealed that eight patients had focal cortical dysplasia (FCD), two had ganglioglioma, one had oligodendroglioma, and one had astrocytoma. The clinical features and MRI findings were largely indistinguishable between the patients with brain tumors and those with FCD, but the patients with brain tumors tended to be younger at the time of seizure onset. Our study shows that surgical treatment of epilepsy in patients with amygdala enlargement usually has a favorable outcome. FCD was the most frequent pathological diagnosis in these patients. However, a brain tumor should be considered in the differential diagnosis, especially in young patients, because it is often difficult to differentiate FCD from a brain tumor on radiological features.

Hippocampal size anomalies in a community-based cohort with childhood-onset epilepsy

OBJECTIVES

Epidemiologic evidence suggests the natural history of refractory mesial temporal lobe epilepsy is complicated, yet little is known about the hippocampus from the nontertiary center perspective.

METHODS

In a community-based cohort, individuals with nonsyndromic focal epilepsy with onset <16 years and controls had research MRI scans. Hippocampal (HC) volumes were manually measured, corrected for total brain volume, and converted to Z scores (Z(HC)) based on the controls' values. Volumes in cases and controls were compared.

RESULTS

Average volumes were not significantly different in cases with unknown cause (n = 117) relative to controls (n = 63). The group with structural and other conditions (n = 23) had significantly smaller volumes. Asymmetry (larger/smaller HC) did not vary among the 3 groups. Hippocampal variances were significantly larger in each epilepsy group relative to controls. In the unknown cause group, 25 (21%) had extreme() values: 15 (13%) with Z(HC) >1.96; 10 (9%) with Z(HC) <-1.96. By contrast, 2/63 (3%) controls had extreme values (p = 0.001). Within the unknown cause group, temporal lobe epilepsy (TLE) cases were more likely to have extreme hippocampal volumes than non-TLE (31% vs 15%, p = 0.03). Extreme volumes were generally interpreted as normal visually. These anomalies were not associated with seizure remission or pharmacoresistance.

CONCLUSIONS

Classic mesial TLE with hippocampal sclerosis is an uncommon finding in the general population. Volume anomalies, both large and small, are often bilateral. The significance of these findings is unclear; however, speculations regarding preexisting hippocampal pathology (e.g., dysplasia) as a factor in TLE and other neocortical epilepsies have been made by others.

Microdysgenesis: Historical roots of an important concept in epilepsy

Microdysgenesis (MD) is a term used to refer to subtle brain dysplasia based on structural tissue characteristics seen exclusively under the microscope. Although MD is often referred to within the field of modern epileptology, the term and its implications have actually evolved over a long period in neurology, starting in the late 19th century. This article undertakes a careful evaluation of original publications in the epilepsy literature and demonstrates that the concept of MD is anchored within a set of papers written from 1890 to 1930 and their contemporaneous reception in classic neuropsychiatric handbooks. Both the text of these early publications and the development of the MD concept are examined and illustrated. This perspective provides insight into historical scientific views of epilepsy as a mental disease that was thought to be dependent largely on hereditary or developmental factors.

Ultrastructural and functional characterization of satellitosis in the human lateral amygdala associated with Ammon's horn sclerosis

The amygdala displays neuronal cell loss and gliosis in human temporal lobe epilepsy (TLE). Therefore, we investigated a certain type of gliosis, called satellitosis, in the lateral amygdala (LA) of TLE patients with Ammon's horn sclerosis (AHS, n = 15) and non-AHS (n = 12), and in autopsy controls. Satellite cells were quantified using light and electron microscopy at the somata of Nissl-stained and glutamic acid decarboxylase-negative projection neurons, and their functional properties were studied using electrophysiology. Non-AHS cases suffered from ganglioglioma, cortical dysplasia, Sturge-Weber syndrome, astrocytoma WHO III-IV, Rasmussen's encephalitis, cerebral infarction and perinatal brain damage. TLE cases with AHS had a more prominent satellitosis as compared to non-AHS and/or autopsy cases, which correlated with epilepsy duration but not age. At ultrastructural level, the predominant type of satellite cells occurring in both AHS and non-AHS cases displayed a dark cytoplasm and an irregularly shaped dark nucleus, whereas perineuronal glial cells with a light cytoplasm and light oval nucleus were much rarer. Satellite cells expressed time- and voltage-dependent transmembrane currents as revealed by patch-clamp recordings typical for 'complex' glia, although only 44% of satellite cells were immunostained for the chondroitin sulfate proteoglycan NG2. Together, the perineuronal cells described here were a heterogenous cell population regarding their NG2 expression, although they resembled NG2 cells rather than bona fide oligodendrocytes and astrocytes based on their ultrastructural and electrophysiological characteristics. Thus, perineuronal satellitosis as studied in the LA seems to be a hallmark of AHS-associated TLE pathology in patients suffering from intractable epilepsy.

Regional neocortical thinning in mesial temporal lobe epilepsy

PURPOSE

To determine the nature and extent of regional cortical thinning in patients with mesial temporal lobe epilepsy (MTLE).

METHODS

High-resolution volumetric MRIs were obtained on 21 patients with MTLE and 21 controls. Mean cortical thickness was measured within regions of interest and point-by-point across the neocortex using cortical reconstruction and parcellation software.

RESULTS

Bilateral thinning was observed within frontal and lateral temporal regions in MTLE patients relative to controls. The most striking finding was bilateral cortical thinning in the precentral gyrus and immediately adjacent paracentral region and pars opercularis of the inferior frontal gyrus, extending to the orbital region. Within the temporal lobe, bilateral thinning was observed in Heschl's gyrus only. Ipsilateral only thinning was observed in the superior and middle temporal gyri, as well as in the medial orbital cortex. Greater asymmetries in cortical thickness were observed in medial temporal cortex in patients relative to controls. Individual subject analyses revealed that this asymmetry reflected significant ipsilateral thinning of medial temporal cortex in 33% of patients, whereas it reflected ipsilateral thickening in 20% of MTLEs.

DISCUSSION

Patients with MTLE show widespread, bilateral pathology in neocortical regions that is not appreciated on standard imaging. Future studies are needed that elucidate the clinical implications of neocortical thinning in MTLE.

Cerebral cavernous malformations and epilepsy

✓Seizures and epilepsy are frequent clinical manifestations of cerebral cavernous malformations (CCMs) and represent the most common symptomatic presentation of supratentorial lesions. Clinicians often diagnose CCMs in patients after a first seizure, or in some cases after obtaining neuroimaging studies in patients suffering from chronic epilepsy previously thought to be idiopathic. In some cases, the lesion is clinically significant solely because of its epileptogenicity, but in others there may be concern about potential hemorrhage or focal neurological deficits from a similar lesion.

The authors present current pathophysiological concepts related to epilepsy associated with CCMs. They discuss the spectrum of seizure disorders associated with these lesions and review the natural history, prognosis, and options for therapeutic intervention.

Management of Focal-Onset Seizures

Focal-onset seizures are manifestations of abnormal epileptic firing of brain cells in a localised area or areas of the brain. The diagnosis of focal-onset seizures initially entails an EEG, a detailed history from the patient and eyewitnesses, as well as computer tomographic or, preferably, magnetic resonance imaging scans. Video EEG to record ictal events may be necessary to establish the correct diagnosis. Focal seizures are classified according to the International Classification of Epileptic Seizures and International Classification of Epilepsies and Epilepsy Syndromes. It is important to try to decide how the seizure event fits into this system in order to successfully evaluate and optimise treatment, as well as to give detailed information to the patient about their seizures and prognosis. Once the decision to treat the seizures has been made, the physician must choose which medication is the most appropriate to begin with. Carbamazepine, phenytoin or valproic acid (sodium valproate) are often rated as first-line drugs, but factors such as adverse-effect profiles, age, possibility of pregnancy, and concomitant diseases and medication also need to be considered. Most of the newer antiepileptic drugs (AEDs) appear to have good efficacy and better tolerability than the older agents, but evidence to support their superiority is scarce and has led to conflicting advice in several guidelines. Among the newer AEDs, lamotrigine, gabapentin, topiramate and oxcarbazepine have obtained monotherapy indication in many countries. The higher costs of the newer AEDs may inhibit their wider use, especially in poorer countries.