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Mesial temporal sclerosis (MTS), also called hippocampal sclerosis, is a pathological entity characterized by neuronal loss and gliosis in the mesial (medial) temporal lobe structures, most notably the hippocampus.
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It is the most common histopathologic finding in patients with medically refractory temporal lobe epilepsy (TLE).
The hippocampus is particularly vulnerable to excitotoxic injury, leading to progressive neuronal loss and gliosis.
| Etiology | Notes |
|---|---|
| Primary (idiopathic) | No clear inciting event; often bilateral |
| Secondary (acquired) | Following febrile seizures, hypoxic injury, status epilepticus, CNS infections, or trauma |
| Developmental factors | Abnormal hippocampal development or migration may predispose |
| Genetic factors | May play a role in familial TLE or dual pathology |
| Feature | Description |
|---|---|
| Temporal lobe epilepsy | Most common presentation; focal seizures with impaired awareness (complex partial seizures) |
| Aura | Deja vu, rising epigastric sensation, fear, olfactory hallucinations |
| Automatisms | Lip-smacking, repetitive hand movements, altered responsiveness |
| Post-ictal confusion | Common in temporal lobe seizures |
| Medically refractory seizures | May require surgical evaluation |
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MRI shows T2/FLAIR hyperintensity and volume loss, especially in coronal planes.
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MR findings:
| Sequence | Appearance |
|---|---|
| T2/FLAIR | Hyperintensity of the hippocampus, especially in the head and body |
| T1-weighted | Volume loss/atrophy of the hippocampus |
| Coronal images | Asymmetric hippocampal shrinkage, loss of internal architecture, increased CSF in temporal horn |
| DWI | May show restricted diffusion in acute post-ictal phase |
| Post-contrast | Typically no enhancement unless recent seizure or inflammation |
Advanced imaging (optional):
| Modality | Role |
|---|---|
| MR volumetry | Quantitative hippocampal asymmetry (cutoff: ~10–15% difference) |
| MR spectroscopy | ↓ N-acetylaspartate (NAA) in affected hippocampus |
| Functional MRI (fMRI) | For memory and language lateralization in pre-surgical planning |
Associated findings:
| Region | Observation |
|---|---|
| Temporal horn of lateral ventricle | Dilated due to hippocampal volume loss |
| Mammillary bodies, fornix, entorhinal cortex | May show signal changes in severe cases |
| Contralateral hippocampus | Assess for bilateral involvement (less common) |