Erhan Bilir

Relative utility of 1H spectroscopic imaging and hippocampal volumetry in the lateralization of mesial temporal lobe epilepsy

Objectives: To determine the relative utility of 1H MRSI and hippocampal volumetry for the lateralization of mesial temporal lobe epilepsy (MTLE) in patients with intractable epilepsy. Background: MTLE is the most common partial-onset seizure disorder in patients undergoing temporal lobe epilepsy surgery. MR volumetry and spectroscopy are reliable preoperative imaging techniques for the lateralization of MTLE. Methods: We analyzed the 1H MRSI and hippocampal formation volumes preoperatively in 30 consecutive patients who had undergone temporal lobectomy. Results: Volumetry correctly lateralized the side of surgery in 93% of patients and1 H MRSI did so in 97% of patients. Incorrect lateralization occurred by volumetry in two patients and by 1H MRSI in one patient. Concordance between all MRI modalities was 73%. Pearsons analysis revealed no correlation between the degree of hippocampal volume loss and the creatine-to-N-acetylated-compounds ratio. Conclusions: Volumetry and 1H MRSI correctly lateralized most patients with MTLE and complement each other in final lateralization. The lack of correlation between the severity of volume loss and the degree of metabolic disturbance suggests that the techniques examine distinct pathophysiologic processes in MTLE.

Association of combined MRI, interictal EEG, and ictal EEG results with outcome and pathology after temporal lobectomy

Summary: Purpose: Magnetic resonance imaging, interictal scalp EEG, and ictal scalp EEG each have been shown to localize the primaly epileptic region in most patients with mesial‐basal temporal lobe epilepsy (MBTLE), but the association of surgical outcome and pathology with each combination of these test results is not known.

Multimodality MRI in mesial temporal sclerosis: Relative sensitivity and specificity

Our objectives were to determine the relative sensitivity and specificity of different MRI sequences and analysis techniques for the detection of mesial temporal sclerosis (MTS). Mesial temporal sclerosis is the most common pathologic finding in patients undergoing temporal lobe epilepsy surgery. Magnetic resonance imaging is the most reliable preoperative imaging technique for the detection of MTS. We analyzed the abnormalities in preoperative MRIs of 44 consecutive patients who had undergone temporal lobectomy and who had pathologic confirmation of MTS. Techniques included inversion recovery (IR); T1-weighted, volume-acquired images; hippocampal T2 relaxometry (HT2); volumetric assessment; and visual analysis. Sensitivity was 86% with IR, 90% with T1-weighted qualitative visual analysis, and 97% with quantitative volumetry. Pathologic prolongation of HT2(>2 SD of normal) was present in 79%. Analysis of variance showed statistically significant differences in sensitivity between HT2, volumetric measurements (p < 0.01), and qualitative visual atrophy (p < 0.05). Concordance between all MRI modalities was 68%. Inversion recovery and qualitative analysis lateralized the side of surgery in 93%. The combination of IR and T1-weighted images correctly identify MTS in most patients. Hippocampal volumetry provided localization in an additional small number of patients.

Quantitative MRI in temporal lobe epilepsy : Evidence for fornix atrophy

Objective: To investigate whether the fornix and mamillary bodies, being part of the limbic system, are abnormal in patients with mesial temporal lobe epilepsy (MTLE). Background: The limbic system comprises the hippocampal formation, fornix, mamillary bodies, thalamus, and other integrated structures. This system is implicated in complex functions, including memory and emotion, and in diseases such as MTLE. Methods: The authors performed volumetric measurements of hippocampus, amygdala, fornix, and mamillary bodies in 50 patients with MTLE and compared the results with normal controls and patients with extratemporal lobe epilepsy. Results: Control (n = 17) measurements of the amygdala, hippocampus, and fornix revealed larger volumes of the right hemisphere structures (p < 0.001). Normalized fornix volumes revealed atrophy in 86% of studies concordant with hippocampal atrophy in all cases but one. Similarly, the mean hippocampal and fornix volumes for the group discriminated the epileptogenic temporal lobe (p < 0.001). Limbic volumes were normal in all patients with extratemporal lobe epilepsy. Conclusions: Quantitative MRI findings support the concept that MTLE is not a process limited to the hippocampus but also involves other interrelated limbic system structures, in particular, the fornix.

Volumetric MRI of the limbic system : anatomic determinants

Abstract The limbic system comprises the hippocampal formation, fornix, mamillary bodies, thalamus, and other integrated structures. It is involved in complex functions including memory and emotion and in diseases such as temporal lobe epilepsy. Volume measurements of the amygdala and hippocampus have been used reliably to study patients with temporal lobe epilepsy but have not extended to other limbic structures. We performed volume measurements of hippocampus, amygdala, fornix and mamillary bodies in healthy individuals. Measurements of the amygdala, hippocampus, fornix and mamillary bodies revealed significant differences in volume between right and left sides (P < 0.001). The intraclass coefficient of variation for measurements was high for all structures except the mamillary bodies. Qualitative image assessment of the same structures revealed no asymmetries between the hemispheres. This technique can be applied to the study of disorders affecting the limbic system.

MRI extrahippocampal volumes and visual memory: correlations independent of MRI hippocampal volumes in temporal lobe epilepsy patients.

Limbic system atrophy and memory dysfunction are common in patients with temporal lobe epilepsy (TLE). However, the relationship between extrahippocampal limbic structures and memory functioning within TLE has received little attention. The present study examined associations of MRI volumetric measurements of the mammillary body, fornix, amygdala, and hippocampus to measures of episodic verbal and visual memory. The Logical Memory and Visual Reproduction subtests from the Wechsler Memory Scale were administered to 47 unilateral TLE patients (25 right, 22 left). Normalized right and left MRI volumes were determined for each patient by cursor tracing 1.5 mm slices from 3D-MRI. Significant associations were found between left hippocampal volume and the immediate, delayed, and percent retention scores of the Logical Memory Test; between the left mammillary body volume and the Logical Memory Test delayed and percent retention scores; immediate Visual Reproduction performance was significantly related to the right and left amygdala volumes, and right mammillary body volume; only the right amygdala and right mammillary body volume were associated with the delayed Visual Reproduction trial. However, neither right nor left hippocampal volumes were related to visual memory performance. Multiple limbic system structural volumes were independently associated with verbal and nonverbal memory performance. Results suggest that visual memory, as measured by the Visual Reproduction Test, may be uniquely associated with extrahippocampal volumes in patients with TLE.

Qualitative MRI Segmentation in Mesial Temporal Sclerosis: Clinical Correlations

Summary: Magnetic resonance imaging (MRI) is reliable and sensitive in the detection of mesial temporal atrophy in patients with temporal lobe epilepsy. We investigated the MRI patterns of atrophy in 47 patients with histologically confirmed hippocampal sclerosis and correlated the imaging findings to the clinical features and surgical outcome. One hundred percent of patients had hippocampal body atrophy, 70% had hippocampal tail atrophy, 23% had amygdala atrophy, and 10% had focal hippocampal body atrophy without other segmental involvement. Correlative analysis of the segmented MRI findings with other clinical variables, including a previous history of childhood febrile convulsions, showed no significant associations except for younger age of seizure onset associated with hippocampal tail atrophy (p < 0.03). No associations between surgical outcome and the patterns of mesial temporal atrophy were detected. Our results demonstrate that variable patterns of atrophy exist in mesial temporal atrophy, but invariably atrophy involves the hippocampal body segment. Segmental MRI analysis in mesial temporal atrophy provides added useful diagnostic information.

Bilateral hippocampal atrophy: consequences to verbal memory following temporal lobectomy.

Background: Bilateral hippocampal damage is a risk factor for memory decline after anterior temporal lobectomy (ATL). Objective: To investigate verbal memory outcome in patients with temporal lobe epilepsy (TLE) with either unilateral or bilateral hippocampal atrophy as measured by MRI. Methods: The authors selected 60 patients with TLE who had undergone ATL (left = 31, right = 29). They determined normalized MRI hippocampal volumes by cursor tracing 1.5-mm slices from three-dimensional MRI acquisition. Hippocampal volumes were defined as atrophic if the volumes were below 2 SD for control subjects. Bilateral hippocampal atrophy was present in 10 patients with left TLE and 11 patients with right TLE. The authors assessed acquisition, retrieval, and recognition components of verbal memory both before and after ATL. Results: Groups did not differ across age, education, intelligence, age at seizure onset, or seizure duration. Seizure-free rates after ATL were 70% or higher for all groups. Before surgery, patients with left TLE displayed worse verbal acquisition performance compared with patients with right TLE. Patients with left TLE with bilateral hippocampal volume loss displayed the lowest performance across all three memory components. After surgery, both groups of patients with left TLE exhibited worse verbal memory outcome compared with patients with right TLE. Bilateral hippocampal atrophy did not worsen outcome in the patients with right TLE. A higher proportion of patients with left TLE with bilateral hippocampal atrophy experienced memory decline compared with the other TLE groups. Conclusion: Bilateral hippocampal atrophy in the presence of left TLE is associated with worse verbal memory before and after ATL compared with patients with unilateral hippocampal volume loss or right TLE with bilateral hippocampal volume loss.

Predictive value of MRI-identified mesial temporal sclerosis for surgical outcome in temporal lobe epilepsy: an intent-to-treat analysis.

Summary: Purpose: Magnetic resonance imaging (MRI) accurately identifies mesial temporal selerosis (MTS), but prediction of successful surgical outcome ranges from 62% to 96% in published studies. Prior investigations only used patients who had received anterior temporal lobectomy (ATL), potentially overestimating the predictive value of MRI‐identified MTS (MRI‐MTS).

Amygdala atrophy and seizure outcome after temporal lobe epilepsy surgery

Surgical outcome in hippocampal atrophy (n = 44) and amygdalohippocampal atrophy (n = 14) were compared. Hippocampal atrophy had better seizure-free outcome than amygdalohippocampal atrophy (80% versus 50%, p = 0.043). Severity of hippocampal atrophy correlated with duration of epilepsy in patients with hippocampal atrophy (r = 0.4, p = 0.007), but not in those with amygdalohippocampal atrophy, suggesting that these two groups may have a different pathogenesis.