On an epilepsy-protocol MRI, a small hippocampus with bright T2/FLAIR signal and loss of internal architecture — plus the secondary signs (fornix, mammillary body, temporal horn) — identifies a surgical target.
Orient first
- The commonest cause of drug-resistant temporal lobe epilepsy in adults.
- Needs thin coronal slices perpendicular to the long axis of the hippocampus; a routine brain MRI misses it.
- Dual pathology (a second lesion such as cortical dysplasia) is common.
Acquire the study
- Epilepsy protocol (HARNESS-MRI type): 3D T1 (1 mm), 3D FLAIR, coronal T2 perpendicular to the hippocampus (≤ 2 mm), SWI (verify local protocol).
The manoeuvre
- Coronal T2 perpendicular to the hippocampus: size compared side to side; loss of internal digitations and stratum radiatum.
- Coronal FLAIR: hyperintensity of the affected hippocampus.
- Secondary signs: ipsilateral fornix and mammillary body atrophy, temporal horn dilatation.
- 3D FLAIR and 3D T1: search the rest of the cortex for dysplasia (blurred grey–white junction, transmantle sign).
What confirms it
- Unilateral hippocampal volume loss with increased T2/FLAIR signal and loss of architecture concordant with EEG.
What licenses you to exclude it
- Symmetric normal hippocampi on a dedicated epilepsy protocol make MTS unlikely; bilateral disease is harder to see.
The classic misread
- Head tilt making one hippocampus look smaller — check symmetry on multiple slices.