Image guided audit of surgery for temporal lobe epilepsy

Beyond localization: the role of traditional neuropsychological tests in an age of imaging

Rapid advances in structural and functional magnetic resonance imaging (MRI) present two significant challenges to the rationale and role of the traditional neuropsychological assessment in the presurgical evaluation of epilepsy surgery candidates today. The first is a direct challenge to the model of material-specific memory that has underpinned much clinical practice over the last 50 years. The second, more fundamental, challenge goes to the very heart of the lateralizing/localizing approach that has been the cornerstone of clinical neuropsychology practice in epilepsy surgery centers to date. This review examines these challenges and suggests some ways in which the profession might respond and adapt. We conclude that noninvasive neuropsychological assessment remains a critical investigation in the presurgical evaluation of epilepsy surgery patients. Its value stretches beyond the localization of a surgically remediable seizure focus. Once a vital test, other investigations are now superior in this respect in many cases. However, new technologies have enhanced the role of the traditional neuropsychological assessment, which is now able to provide unparalleled insights and predictions into the way in which the underlying pathology, seizures, and proposed surgery shape an individual's profile of cognitive abilities. Detailed neuropsychological feedback enables the patient to make an informed decision, and forms the basis of the tailor made preemptive rehabilitation programs that can be implemented preoperatively, minimizing the most significant morbidity associated with epilepsy surgery today.

Comparison of two different measurement techniques of hippocampal resection length in temporal lobe epilepsy: results of a prospective study

BACKGROUND

Magnetic resonance imaging (MRI) volumetry has evolved to a highly sensitive method for presurgical detection of hippocampal sclerosis in temporal lobe epilepsy (TLE). Seizure resolution and neuropsychological sequelae are believed to correlate with extent of resection. Therefore an easy volumetric method to determine extent of resection is desirable. The purpose of this work is to evaluate and compare two different measurement techniques for hippocampal resection length.

METHODS

Sixty-one patients with a mean seizure history of 25.1 years and medically intractable TLE were included. They underwent MRI with sagittal acquired 3D T1-weighted spoiled gradient recalled echo sequence in 1 mm(3) isotropic voxel. Hippocampal resection length was calculated with two different methods. In the slice counting method (SCM) the number of consecutive 1-mm-thick slices containing resected hippocampus formation was counted. In the vector method (VM) the sum of the oblique and thus longer distances between the centre points of segmented hippocampal areas on each MRI slice were calculated.

RESULTS

Since the hippocampus is a curved body, the resection lengths measured with VM were always larger than measured with SCM. The comparison of resection length expressed in "percent of total length" showed good agreement between the two methods, because unlike the absolute values of resection length, the percentage values are unaffected by the three-dimensional shape of the hippocampus.

CONCLUSION

The easier and quicker method of "slice counting" may be used to determine resection length expressed in "percent of total length", giving reliable values for resection length but causing less volumetric work.

Comparison of manual tracing versus a semiautomatic radial measurement method in temporal lobe MRI volumetry for pharmacoresistant epilepsy

INTRODUCTION

The aim of this study was to test a modified radial semiautomated volumetry technique (radial divider technique, RDT) versus the manual volumetry technique (MVT) for proportionality of temporal subvolumes in 30 patients with drug-resistant temporal lobe epilepsy.

METHODS

Included in the study were 30 patients (15 female, 15 male; mean age 39.6 years) with pharmacoresistant epilepsy (mean duration 26.6 years). MRI studies were performed preoperatively on a 1.5-T scanner. All image processing steps and volume measurements were performed using ANALYZE software. The volumes of six subregions were measured bilaterally; these included the superior temporal gyrus (STG), middle + inferior temporal gyrus (MITG), fusiform gyrus (FG), parahippocampal gyrus (PHG), amygdala (AM), and hippocampus (HP). Linear regression was used to investigate the relationship between the comparable subvolumes obtained with MVT and RDT.

RESULTS

Very high correlations (R (2) >0.95) between RDT and MVT were observed for the STG + MITG and the STG + MITG + FG, but low correlations for the PHG subvolumes and the combined PHG + HP + AM subvolumes. These observations were independent of the side of the pathology and of hemisphere.

CONCLUSION

The two measurement techniques provided highly reliable proportional results. This series in a homogeneous group of TLE patients suggests that the much quicker RDT is suitable for determining the volume of temporolateral and laterobasal temporal lobe compartments, of both the affected and the non-affected side and the right and left hemisphere.

Psychosocial and Neurobehavioral Factors Related to Surgical Treatment for Partial Epilepsy: A Multivariate Analysis

Studies of temporal lobe surgery rarely include anatomical and neurobehavioral data in the analysis of outcome. We carried out a retrospective study on 50 patients, using clinical data from case notes, resection volumes, and preoperative imaging data. Three main conclusions emerge from this study: (1) Psychosocial outcome is related to postoperative seizure control. (2) Late postoperative aggression and clinical depression are associated with bad psychosocial outcome. (3) Right-sided hippocampal sclerosis, as suggested by measurements with T2 relaxometry, correlates with interictal psychopathology, as measured with the Beck Depression Inventory, the Leyton Obsessional Inventory, and the Bear-Fedio personality inventory.

Analysis of temporal lobe resections in MR images

PURPOSE

The nature of the resection in surgery for intractable medial temporal lobe epilepsy is likely to be a principal factor determining seizure and neuropsychological outcome. However, there is no universally accepted system for describing the characteristics of individual resections to allow comparison between patients and patient groups treated at different institutions. We therefore developed a technique of volumetric analysis of temporal lobe resections.

METHODS

With comparison of coregistered pre- and postoperative, volumetric magnetic resonance imaging (MRI) scans in 10 subjects, the volumes of six temporal lobe substructures were determined by manual delineation in the pre- and post-operative images for each case, allowing the extent of resection to be determined.

RESULTS

The substructures and their extent of resection were measured with acceptable repeatability in each case.

CONCLUSIONS

We developed a reliable method for the quantitative description of temporal lobe resections. This will be of application in determining the relation between the anatomic nature of the resection in intractable epilepsy and the seizure and neuropsychological outcome.

Image-directed neurosurgery

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