Diffusion tensor imaging in temporal lobe epilepsy

Although mesial temporal sclerosis (MTS) has long been recognized in association with temporal lobe epilepsy (TLE), there is a growing body of literature suggesting structural abnormalities extending beyond the temporal lobe in patients with TLE. Diffusion tensor imaging (DTI) is a novel imaging technique that provides insight into the structural integrity of cerebral white matter. DTI studies have demonstrated extensive bilateral white matter abnormalities in TLE that extend far beyond the temporal lobe, even in patients with unilateral MTS. The relationship between white matter abnormalities, seizures, and comorbidity in TLE remains unclear.     

Extratemporal white matter abnormalities in mesial temporal lobe epilepsy demonstrated with diffusion tensor imaging

PURPOSE: Recent studies have demonstrated bilateral white matter abnormalities in temporal lobe epilepsy (TLE) patients with unilateral mesial temporal sclerosis (MTS). The purpose of this project was to determine whether abnormalities of water diffusion are seen in extratemporal white matter of patients with TLE and pathologically confirmed MTS and to determine whether these findings are associated with worse surgical outcome. METHODS: Eleven patients with TLE and unilateral MTS confirmed in surgical specimens and 14 controls were studied by using cerebrospinal fluid-suppressed diffusion tensor imaging (DTI) and T2 relaxometry. RESULTS: Hippocampal T2 signal for patients was significantly elevated both ipsilateral (p<0.001) and contralateral (p=0.006) to MTS. DTI demonstrated reduced fractional anisotropy of the genu of the corpus callosum (p=0.003) and external capsule (p=0.02) and elevated mean diffusivity of the genu (p=0.005), splenium (p=0.03), and external capsule (p<0.001). For both the genu and external capsule, parallel diffusion of patients was not different from that of controls (genu, p=0.81; external capsule, p=0.45), whereas perpendicular diffusion was elevated (genu, p=0.001; external capsule, p<0.001). With mean postsurgical follow-up of 18.5 months, eight of 11 patients were entirely seizure free and the remaining three had all experienced a worthwhile reduction in seizure frequency. CONCLUSIONS: Our findings suggest that although patients with TLE and MTS have extensive bilateral and extratemporal pathology, these findings may not be associated with a worse postsurgical outcome.     

颞叶内侧结构弥散张量成像及白质纤维束成像在颞叶癫痫诊断中的应用价值

目的 通过磁共振弥散张量成像(DTI)及白质纤维束示踪(DTT)技术定量分析颞叶癫痫患者双侧颞叶内侧结构弥散参数值及局部纤维束变化特点,评价DTI技术对颞叶癫痫的诊断价值.方法 对广州医学院第二附属医院自2010年12月至2011年2月临床诊断为颞叶癫痫的16例患者和20例健康志愿者进行常规MRI及DTI扫描,测量双侧颞叶杏仁体、海马及颞叶皮质的部分各向异性(FA)、相对各向异性(RA)、表观弥散系数(ADC)等数值并进行统计学分析,同时应用DTT技术观察癫痫患者局部纤维束与正常对照者的差异.结果 正常对照者双侧颞叶内侧各结构FA、RA、ADC值比较差异均无统计学意义(P＞0.05).颞叶癫痫患侧、对侧与正常对照者颞叶内侧各结构FA、RA、ADC值比较差异均有统计学意义(P＜0.05),其中ADC值呈颞叶癫痫患侧＞颞叶癫痫对侧＞正常对照者的变化趋势,以海马尾部变化最为显著;而FA、RA值呈颞叶癫痫患侧＜颞叶癫痫对侧＜正常对照者的变化趋势,并且杏仁体、海马体部变化较海马尾部更显著.结论 DTI技术能充分了解癫痫患者颞叶内侧结构的弥散参数值及纤维束变化特点,有助于癫痫病灶定位的准确诊断,同时加深对颞叶内侧结构整体变化的了解亦有助于术前的整体评估及提高手术疗效.     

Abnormalities in diffusion tensor imaging of the uncinate fasciculus relate to reduced memory in temporal lobe epilepsy

Aims: To use Diffusion Tensor Imaging (DTI) to explore structural integrity and connectivity of the uncinate fasciculus (UF) in patients with temporal lobe epilepsy (TLE) and its relationship to memory performance.
Methods: DTI and UF reconstruction were performed in 28 patients with TLE (18 left, 10 right) and 10 normal controls. Differences between left and right UF fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values and correlations between DTI measures and memory scores in the TLE groups were computed.
Results: In controls, FA was higher in the left than right UF (p < 0.01). In left TLE, FA values were lower and ADC values higher than controls in the left UF and ADC values were higher in the right UF (all p < 0.05). In right TLE, ADCs were higher in the left and right UF compared to controls, and FA was reduced in the left UF (all p < 0.05). In left TLE, ADCs in the left UF were negatively correlated with Auditory Immediate (p < 0.05) and Delayed Memory (p < 0.01). Visual Delayed Memory was positively correlated with reduced FA in the ROI of the right UF and increased radial diffusivities (p < 0.05). No significant correlations were found in right TLE. Thus, DTI values correlated with memory scores in the expected direction in patients with left TLE.
Conclusions: Abnormal diffusion measures in the UF ipsilateral to the epileptogenic zone suggest that integrity of the UF is related to memory performance in patients with left TLE. Larger sample sizes are needed to evaluate structure-function correlations further.     

A meta-analysis of white matter changes in temporal lobe epilepsy as studied with diffusion tensor imaging

Purpose: Diffusion tensor imaging (DTI) is used increasingly to study white matter integrity in people with temporal lobe epilepsy (TLE). Most studies report fractional anisotropy (FA) decrease and mean diffusivity (MD) increase in multiple white matter regions. The disturbance of white matter integrity varies across studies and between regions. We aimed to obtain a more consistent estimate of white matter diffusion characteristics and relate these to the distance from the seizure focus. Methods: Studies comparing diffusion characteristics of people with epilepsy with those of healthy controls were systematically reviewed and quantified using random and mixed effects meta analysis. In addition to the overall meta‐analysis, pooled FA and MD differences were determined per hemisphere and white matter category separately. Key Findings: We included 13 cross‐sectional studies. The pooled FA difference for all white matter was ?0.026 (95% confidence interval [CI] ?0.033 to ?0.019) and MD difference was 0.028 × 10^?3 mm²/s (95% CI 0.015–0.04). FA was reduced significantly in people with TLE compared with healthy controls in both ipsilateral (mean difference ?0.03) and contralateral white matter (?0.02). MD was significantly increased ipsilaterally and contralaterally. MD differed significantly between white matter connected to the affected temporal lobe and remote white matter. Significance: The meta‐analysis provides a better estimation of the true diffusion characteristics. White matter structural integrity in TLE is disturbed more severely in the ipsilateral than in the contralateral hemisphere, and tracts closely connected with the affected temporal lobe are most disturbed. The exact underlying mechanisms remain to be elucidated.     

前颞叶切除范围与视野缺损关系的弥散张量成像分析

目的 观察颞叶癫痫患者前颞叶切除术后视野缺损的发生率以及手术切除范围与视野缺损的关系.方法 25例前颞叶切除术的患者于术前及随访时行视野、磁共振(含DTI弥散张量序列)检查,根据视野缺损严重程度的不同将患者分为A、B、C三级.手术后视放射的各向异性分数(FA值)的下降(△FA)代表Meyer袢受损情况.比较不同视野缺损组之间前颞叶切除范围的差异;并对切除范围和△FA进行线性相关分析.结果 前颞叶切除术后22例患者出现象限盲.前颞叶平均切除长度:A组31.1 mm,B组42.5 mm,C组50.4 mm,A＜B＜C组(P＜0.05).手术侧的△FA与切除范围旱线性相关.结论 前颞叶切除术破坏视放射导致视野缺损较常见.有必要术前应用DTI获得患者视放射的信息,进行术前风险评估.

Abstract：

Objective Anterior temporal lobectomy(ATL) for temporal lobe epilepsy (TLE) is the most commonly performed epilepsy surgery procedure.A visual field defect(VFD) due to the injury to the optic radiation may occur after ATL.DTI technique can visualize the optic radiation (OR) noninvasively.This study aimed at evaluating the incidence of VFD after ATL and investigating whether the resection size of lateral ATL correlated with the extent of VFD.We tried to explain the impact of ATL on the OR and to investigate the anterior extending of Meyer loop with DTI technology.Method 25 patients( 14male, 11 female) underwent ATL for treatment of epilepsy.The patients were aged from 13 to 39 years old ( mean age:22.4 yrs).All cases were classified into three groups on the basis of the severity of VFD( A ～ C,with group C the most severe).All patients had preoperative and follow up clinical and MRI( including DTI series) examinations.The clinical and MRI(DTI) outcomes of these patients were retrospectively analyzed.Results At mean follow up period of 31.3 weeks ( range, 17 - 42 weeks), we found 22 patients become quadrantanopia due to the injury to OR after ATL.A significant reduction of fractional anisotropy was demonstrated in the OR on the side of the temporal lobectomy.The severity of VFD decreased according to the reducing of the mean resection size(group A, 31.1 mm;group B 42.5 mm;C, 50.4 mm), P ＜0.05.There was linearship between the resection size and the FA decrease.Conclusions VFD due to the injury to the OR was not uncommon after ATL There was an association between the resection size and severity of VFD.Optic radiation showed a decreased FA value in cases after ATL.There is considerable intersubjective variance about the OR, so it is necessary to get the patient's DTI information about the OR before the operation ,which could help to assess the preoperative risks.     

颞叶癫痫患者磁共振弥散张量成像及记忆损害的研究

目的利用磁共振弥散张量成像技术(DTI)研究颞叶癫痫(TLE)患者脑内微观改变及记忆损害的相关脑区。方法对颞叶癫痫患者15例和健康对照者15例,进行DTI检查,利用韦氏记忆量表检测记忆功能。结果 TLE患者部分各向异性弥散(FA)值降低激活区域有颞叶、边缘叶、扣带回和岛叶,升高区有:额叶、顶叶、枕叶,表观系数(ADC)值升高激活区域在颞叶、额叶、枕叶、顶叶;无ADC值降低区域。与健康者相比,颞叶癫痫患者的记忆商数(MQ)(90.73±19.72)显著下降,P<0.01。对照组FA值在左岛叶、颞叶与MQ值正相关;患者组FA值在右额、顶、枕叶、左顶叶与MQ值正相关,在左颞叶与MQ值负相关。对照组ADC与MQ正相关区域在左边缘叶,与MQ成负相关区域在左顶叶、患者组正相关区域在左、右颞叶。结论初步证实TLE患者的脑内结构变化不局限于颞叶,还包括颞叶外网络结构;TLE患者全脑DTI与MQ存在着相关激活脑区,表明记忆功能损害与脑内相关结构改变有关。     

Diffusion tensor analysis of temporal and extra-temporal lobe tracts in temporal lobe epilepsy

OBJECTIVE: To determine whether the major temporal lobe white matter tracts in patients with temporal lobe epilepsy manifest abnormal water diffusion properties. METHODS: Diffusion tensor MRI measurements were obtained from tractography for uncinate, arcuate, inferior longitudinal fasciculi and corticospinal tract in 13 children with left temporal lobe epilepsy and normal conventional MRI, and the data were compared to measurements in 12 age-matched normal volunteers. The relationship between tensor parameters and duration of epilepsy was also determined. RESULTS: All four tracts in the affected left hemisphere showed lower mean anisotropy, planar and linear indices, but higher spherical index in patients versus controls. Diffusion changes in the left uncinate and arcuate fasciculus correlated significantly with duration of epilepsy. Arcuate fasciculus showed a reversal of the normal left-right asymmetry. Various diffusion abnormalities were also seen in the four tracts studied in the right hemisphere. CONCLUSION: Our findings indicate abnormal water diffusion in temporal lobe and extra-temporal lobe tracts with robust changes in the direction perpendicular to the axons. Diffusion abnormalities associated with duration of epilepsy suggest progressive changes in ipsilateral uncinate and arcuate fasciculus due to chronic seizure activity. Finally, our results in arcuate fasciculus are consistent with language reorganization to the contralateral right hemisphere.     

Diffusion tensor imaging in frontal lobe epilepsy

We report a 13-year-old female with refractory frontal lobe epilepsy in whom diffusion tensor imaging was useful for exploring subtle cortical malformation. She had frequent simple partial seizures characterized by clonic movement of the right upper extremity. Conventional magnetic resonance imaging was not conclusive. A diffusion tensor imaging revealed an increased apparent diffusion coefficient and reduced anisotropy in the left frontal lobe. Positron emission tomography disclosed hypermetabolism in the adjacent area. We could identify the relatively thick cortex with an indistinct gray-white matter junction in a thin-slice T(1)-weighted image.     

Quantitative neuropathology and quantitative magnetic resonance imaging of the hippocampus in temporal lobe epilepsy

The aims of this study were to examine the relationships of hippocampal T2 (HCT2) relaxation time and magnetic resonace (MR)-based hippocampal volume (HCV) to neuronal (ND) and glial cell densities (GD) of hippocampal neuronal cell layers, and to obtain a better clinicopathological definition of hippocampal sclerosis (HS) and end folium sclerosis (EFS). Fifty-three hippocampi with HS, 6 with EFS, and 6 control hippocampi were studied. Pathologically, the HS group had a significantly higher logarithm (log) GD/ND than the controls in all hippocampal subregions, and than the EFS group in all subregions except the granule cell layer of the dentate gyrus (GCDG). The EFS group had a significantly higher log GD/ND than the control group only in the GCDG. Clinical correlations suggested that EFS may be the consequence of temporal lobe seizures and not an epileptogenic entity. Hippocampal atrophy in HS was associated with neuronal cell depletion and concomitant gliosis in the cornu Ammonis (CA) 1, CA2, CA3, and hilus. An increased HCT2 was associated with damage in the CA1 and also the hilus and has a different neuropathological basis than HCV loss. MR-based HCV measurement and HCT2 mapping, therfore, give complementary information in the presurgical evaluation of temporal lobe epilepsy and longitudinal studies.     

Secondary white matter degeneration of the corpus callosum in patients with intractable temporal lobe epilepsy: a diffusion tensor imaging study

Imaging changes in patients with focal epilepsy are not only seen in areas where seizures arise but often also in remote locations. The mechanism for such changes is unknown. We aimed to investigate whether patients with temporal lobe epilepsy (TLE) have microstructural changes involving the posterior portion of the corpus callosum (CC), where it links the temporal lobes, using presurgical diffusion tensor imaging (DTI) sequences. Ten patients with medically intractable TLE (two mesial TLE, eight neocortical TLE) who had seizure-free surgical outcomes were compared with 10 healthy controls. The regions of interest were outlined at each Witelson region (WR). Fractional anisotropy (FA), apparent diffusion coefficient (ADC) and three principal diffusivity values (lambda1, lambda2, lambda3) were determined in each WR. We performed tractography originating at each WR. In the TLE patients, the FA values were lower at the splenium of the corpus callosum (WR 7) compared to controls (p<0.05). Analysis of Eigen values in that location revealed that lambda1 values were decreased while lambda2 and lambda3 values were increased (p<0.05). Tractography revealed the connection between both temporal lobes via WR 7. In conclusion, decreased FA values with decreased lambda1 and increased lambda2 and lambda3 at the splenium of CC suggest that the pathologic changes, Wallerian degeneration, extend to the corpus callosum in TLE patients. Seizure-induced damage may cause secondary white matter degeneration along the tapetum and through the splenium of the corpus callosum, a potential pathway of spread in temporal lobe seizures.     

左侧颞叶癫痫患者执行功能损害与钩束弥散张量成像参数的相关性

目的 应用神经心理学方法和磁共振弥散张量成像(diffusion tensor imaging,DTI)技术研究左侧颞叶癫痫(temporal lobe epilepsy,TLE)患者执行功能损害的特点及与其双侧钩束(uncinate fasciculus,UF)DTI参数的关系.方法 对14例成人左侧TLE患者(患者组)和15名健康对照者(对照组)进行执行功能的神经心理检查(包括stroop、数字广度、数字符号、连线试验及词语流畅性)评分,并对两组受试者均进行DTI扫描.结果 患者组stroop错误数[(7.20±3.60)vs.(1.60±0.60)]高于对照组(P＜0.05),数字广度[(12.30±6.20)vs.(17.60±2.10)]、数字符号[(50.33±16.10)vs.(66.04±10.12)]及词语流畅性[(12.05±5.36) vs.(19.33±2.55)]均低于对照组(P＜0.05),stroop反应时[(23.86±10.91)vs.(16.36±6.13)]及连线试验的时间[(56.11±20.12)vs.(40.43±15.07)]均长于对照组(P＜0.05).与对照组相比,患者组左侧钩束各向异性(Fractional Anisotrophy,FA)值降低[(0.332±0.043)vs.(0.379±0.014)],差异具有统计学意义(P＜0.05).相关分析示,患者组左侧钩束FA值与词语流畅性(r=0.56,P=0.025)及数字广度(r=0.58,P=0.028)呈正相关.结论 左侧TLE患者存在广泛的执行功能损害,部分执行功能的损害与左侧钩束的损害相关,左侧钩束的损害可能是部分执行功能损害的病理生理基础.     

Qualitative and quantitative imaging of the hippocampus in mesial temporal lobe epilepsy with hippocampal sclerosis

MR imaging allows the in vivo detection of hippocampal sclerosis (HS) and has been instrumental in the delineation of the syndrome of mesial temporal lobe epilepsy with HS (mTLE-HS). MR features of HS include hippocampal atrophy with an increased T2 signal. Quantitative MR imaging accurately reflects the degree of hippocampal damage.Ictal single photon emission computed tomography (SPECT) in mTLE-HS shows typical perfusion patterns of ipsilateral temporal lobe hyperperfusion, and ipsilateral frontoparietal and contralateral cerebellar hypoperfusion. Interictal 18fluoro-2-deoxyglucose positron emission tomography (PET) shows multiregional hypometabolism, involving predominantly the ipsilateral temporal lobe. 11C-flumazenil PET shows hippocampal decreases in central benzodiazepine receptor density. Future strategies to study the etiology and pathogenesis of HS should include longitudinal MR imaging studies,MR studies in families with epilepsy and febrile seizures, stratification for genetic background, coregistration with SPECT and PET, partial volume correction and statistical parametric mapping analysis of SPECT and PET images.     

MRI正常额叶癫(癎)患者的MR扩散张量成像研究

目的应用MR扩散张量成像（DTI）技术探讨MRI正常的额叶癫痢患者与运动相关白质是否存在隐匿性病变。方法对临床确诊的16例MRI正常的额叶癫痫患者发作间期和30例健康志愿者行常规MRI和DTI检查,定量测量额叶皮层下白质、胼胝体膝部和压部、内囊前肢和后肢及外囊的平均扩散系数（DCavg）和部分各向异性（FA）值,并进行统计学分析。结果MRI正常的额叶癫痴患者额叶皮层下白质、胼胝体膝部区域的DCavg值显著高于正常人（P〈0．01）,皮层下白质的FA值显著低于正常人（P〈0．01）,胼胝体膝部的FA与正常人无差异。结论MRI正常的额叶癫痫患者存在额叶隐匿性损害DTI为发现致痢灶提供理论依据,具有临床应用价值。     

Group‐specific regional white matter abnormality revealed in diffusion tensor imaging of medial temporal lobe epilepsy without hippocampal sclerosis

Purpose: In comparison to temporal lobe epilepsy (TLE) patients with hippocampal sclerosis (TLE‐HS), TLE patients without HS (TLE‐NH) have a similar clinical course but may result in worse surgical outcome. We investigated whether the clinical features related to the lack of HS in TLE patients (TLE‐NH) can be explained by water diffusion abnormalities throughout diffusion tensor imaging (DTI) by voxel‐based analysis. Methods: Nineteen patients with TLE‐HS (left/right TLE 12:7), 18 patients with TLE‐NH (left/right TLE 10:8), and 20 controls were included in the study. By statistical parametric mapping (SPM2), the diffusion properties specific to disease characteristics (TLE‐HS vs. TLE‐NH) were analyzed. Results: In TLE‐HS, we found the areas of increased mean diffusivity (MD) in their ipsilateral temporal and extratemporal areas including the hippocampus, parahippocampal, and frontoparietal regions. Left TLE‐HS showed a characteristic MD increase in the ipsilateral posterior cingulum, isthmus of corpus callosum, and contralateral occipital and temporal regions, which was not observed in right TLE‐HS group. In left TLE‐NH, two regions of increased MD were observed in the ipsilateral posterior fornix (within fusiform gyrus) and posterior cingulum. Right TLE‐NH did not show any increased MD. Discussion: In left TLE‐NH, we could find the water diffusion change along the posterior cingulum, which was quite different from the extensive abnormality from TLE‐HS. In addition, there was a lesion‐side–specific distribution (left predominant) of pathology in mesial TLE. This provides a possibility that TLE‐NH is a heterogenous or entity different from TLE‐HS.