Magnetic resonance volumetric analysis of hippocampi in children in the age group of 6-to-12 years: a pilot study

Abstract

Atrophy of the mesial temporal structures, especially the hippocampus, has been implicated in temporal lobe epilepsy. However, to date, there is very scant data regarding normal volumes of the hippocampus in the pediatric population. This is a pilot study to estimate the normal volumetric data for the Indian pediatric population between 6 and 12 years of age. We have also tried to understand whether age and gender have an effect on the hippocampal volumes in this age group. The study group comprised 20 children, 6-12-years old without history of epilepsy or other neurological deficits. There were nine boys and 11 girls. All scans were performed on a 1.5T GE echo speed scanner. 3D fast SPGR sequence was prescribed in the coronal plane. The images were post-processed on an Advantage Windows 3.1 workstation. Using an automated program, the same observer calculated the hippocampal area, in cubic centimeters, clockwise and anticlockwise. The clockwise/anticlockwise data were subjected to correlation analysis for detecting intra-observer agreement. The mean and SD for left and right hippocampal volumes were estimated. The lower and upper limits for normal hippocampal volumes were determined using 95% (+/- 2SD) limits on either side of the mean. In order to understand the effect of age on various hippocampal volumes we performed regression analysis. Mann-Whitney's test was used to test the significance of differences for gender variations. Correlation analysis established that there was intra-observer agreement. In the Indian pediatric population we have found the mean right hippocampal volume (RHV) to be 2.75 cm(3) and mean left hippocampal volume (LHV) to be 2.49 cm(3). Mean hippocampal volume was found to be 2.67 cm(3) (SD = 0.42). The upper and lower limits for hippocampal volumes were 3.51 cm(3) and 1.83 cm(3), respectively, based on 95% (+/- 2SD) limits on either side of the mean. There was no effect of age or gender on the hippocampal volumes. In the Indian pediatric population we determined hippocampal volumes in a small series of healthy children. We found that hippocampal volumes < or =1.83 cm(3) (< or =2SD) can be considered to be abnormal. These findings can be used as normative data to evaluate cases of hippocampal sclerosis in the Indian population.