Epilepsy Linked To Shrinkage In Both Hippocampi

What was studied

This study combined results from many MRI studies to measure how much the hippocampus is smaller in adults with mesial temporal lobe epilepsy (mTLE). The hippocampus is a brain area often involved in this type of epilepsy.

The researchers did a systematic review and meta-analysis, which means they searched multiple databases and trial registries, selected studies using set rules, and pooled the results. They included studies of adults with epilepsy on one side of the brain who had MRI scans before surgery, along with healthy control groups. In total, 28 studies were included, and 23 of those had enough data for the main analysis, covering 803 patients and 613 controls.

What they found

Compared with healthy controls, adults with mTLE had a smaller hippocampus on the same side as the seizure focus. On average, the difference was about 985 mm3.

The hippocampus on the opposite side was also smaller, but by a much smaller amount. On average, the difference was about 199 mm3. The authors said this pattern was consistent with marked ipsilateral atrophy and a smaller, consistent contralateral reduction, in line with partial bilateral structural involvement.

The study did not find evidence of small-study effects, and the overall risk of bias was rated low to moderate.

Limits of the evidence

This meta-analysis pooled observational MRI studies, so it cannot show from these data alone why the volume differences were present.

The studies varied a lot from each other, and the statistical heterogeneity was high. That means the exact size of the volume differences was not the same across studies, so the average numbers should be used with caution.

The abstract only describes adults with unilateral mTLE who had presurgical MRI. It does not tell us whether the same findings apply to children, people who are not surgery candidates, or other epilepsy types. The abstract also does not explain which factors might affect hippocampal size, such as seizure duration, medications, or MRI methods.

For families and caregivers

For families, this study suggests that in mTLE, the hippocampus is usually smaller on the side where seizures start, and there may also be smaller changes on the other side.

This may matter because pooled estimates may help with quantitative MRI in presurgical evaluation. Still, these results are group averages from research studies. They cannot by themselves tell what is happening in one specific person or predict treatment outcomes.

What to watch next

Further research could use more standardized MRI methods and examine how these volume measurements relate to clinical features and presurgical evaluation in individual patients.

Terms in this summary

mesial temporal lobe epilepsy (mTLE)

A type of epilepsy in which seizures start in deep parts of the temporal lobe, often involving the hippocampus.

hippocampus

A brain structure important for memory and often involved in temporal lobe epilepsy.

hippocampal atrophy

Shrinkage or loss of volume in the hippocampus.

meta-analysis

A study that combines results from multiple studies to get an overall estimate.

ipsilateral

On the same side as the seizure focus.

contralateral

On the opposite side from the seizure focus.

volumetry

A way of measuring the size or volume of a body part, such as the hippocampus, on MRI.

heterogeneity

How much the results differ across studies.