Hippocampal volume loss in mesial temporal lobe epilepsy: Magnitude and laterality in a meta-analysis of MRI volumetry studies.

BACKGROUND

Hippocampal atrophy is a defining structural feature of mesial temporal lobe epilepsy (mTLE), yet the magnitude of volume loss and the extent of contralateral involvement vary across magnetic resonance imaging (MRI) studies, limiting quantitative interpretation in clinical practice. We conducted a systematic review and meta-analysis to quantify hippocampal volume reduction in adults with mTLE and assess the consistency of contralateral changes.

METHODS

Following PRISMA 2020 guidelines, we searched six bibliographic databases and different trial registries. Eligible studies included adults with unilateral mTLE who underwent pre-surgical structural MRI with quantitative hippocampal volumetry, as well as healthy controls. Two reviewers independently assessed risk of bias using ROBINS-E. Random-effects meta-analyses pooled mean differences in absolute hippocampal volume (mm3; controls minus patients) for hippocampi ipsilateral and contralateral to the seizure focus.

RESULTS

Twenty-eight studies met the inclusion criteria; 23 contributed to the meta-analysis (803 patients, 613 controls). Ipsilateral hippocampal volume was significantly reduced (mean difference 985.2 mm3, 95% CI 759.7-1210.7; p < 0.001; I2 = 98%). Contralateral volume was also reduced (22 studies; mean difference 198.8 mm3, 95% CI 124.4-273.3; p < 0.001; I2 = 85%). Funnel plot inspection and Egger testing showed no evidence of small-study effects. ROBINS-E indicated low to moderate risk of bias overall.

CONCLUSIONS

Adult mTLE shows marked ipsilateral hippocampal atrophy with a smaller, consistent contralateral reduction, consistent with partial bilateral structural involvement. Pooled estimates provide clinically interpretable reference values for quantitative MRI in presurgical evaluation, though substantial heterogeneity warrants caution.