ROLE OF HIPPOCAMPAL VOLUMETRY IN PATIENTS OF MESIAL TEMPORAL LOBE EPILEPSY WITH MR IMAGING

Abstract

Background: Unilateral hippocampal sclerosis (HS) is the most frequent pathological finding in temporal lobe epilepsy (TLE) . Visual (qualitative) assessment of T2-weighted changes (hyperintense signal on T2- weighted images and atrophy) was the earliest method that demonstrated an association among hippocampal pathology and MR-detectable signal abnormality. Hippocampal volume loss is a sensitive and specific pointer of hippocampal sclerosis in the clinical setting of epilepsy, and hippocampal volumetric study can quantify atrophy in TLE patients.

OBJECTIVES: Role of MR hippocampal Volumetry in patients of mesial temporal lobe epilepsy and to establish normative MR hippocampal volumetric data in controls.

Study design: Observational Comparative study

Participants: 30 patients with established diagnosis of MTLE on clinical and EEG basis. Control group comprises of non-epileptic cases with no abnormality on brain MRI

Materials and Methods: Visual assessment and hippocampal volumetry were done on oblique coronal T2W images. Cross sectional area of both the hippocampus were measured in these oblique coronal images. Manual segmentation and volumetry were done using Siemens syngo software. The anterior hippocampus was tak­en from the point where the cerebro-spinal fluid (CSF) , in the uncal recess of temporal lobe or alveus was seen. The posterior margin was taken on the MR image where the crus of fornix was seen in full profile. CSF in the lateral ventricle was taken as lateral border. CSF in the cistern ambiens was taken as medial border. The gray white junction between the subiculum white matter of parahippocampal gyrus was taken as inferior landmark. The alveus and the CSF within the lat­eral ventricle was used as superior landmark. The right and left hippocampi were measured separately. The region of interest (ROI) was manually traced using a com­puter mouse. The total area was obtained by adding all the areas from each slice. The hippocampal area was obtained by adding up all the areas from each slice. The hippocampal volume was obtained by multiplying the total area with the slice thickness (in cms) .

Results: Quantification of hippocampal volume by MRI increases the detection of subtle signs of unilateral and bilateral Hippocampal Sclerosis in 73%. Out of the 30 patients, visual analysis revealed hippocampal sclerosis in 17 (56.6%) patients and visually normal MR imaging findings in 11 (36.6%) patients. Out of these visually assessed normal patients, hippocampal volumetry detected volume loss in 5 out of 13 patients (38.4%) .

Conclusion: Patients with intractable temporal lobe epilepsy have smaller mean hippocampal volume ipsilateral to seizure focus. Visual assessment and volumetry show equal efficacy in diagnosing unilateral pathology, but quantitative technique are more sensitive in diagnosing bilateral pathologies and mild unilateral pathology.

Implications: Patients with MTLE should be subjected to hippocampal volumetry