A 32-year-old woman with a 5-year history of focal seizures originating from the temporal lobe undergoes neuroimaging as part of pre-surgical evaluation. Which is the most common structural lesion found in patients with temporal lobe epilepsy?

Explanation

## Most Common Structural Lesion in Temporal Lobe Epilepsy **Key Point:** Hippocampal sclerosis (HS) is the most frequent structural abnormality identified in patients with temporal lobe epilepsy (TLE), accounting for approximately 50–70% of surgically-treated TLE cases. ### Pathophysiology of Hippocampal Sclerosis 1. **Neuronal loss and gliosis** in the hippocampus, particularly affecting CA1 and CA3 regions 2. **Mossy fibre sprouting** leads to recurrent excitatory circuits 3. **Loss of inhibitory interneurons** reduces GABAergic tone 4. Results in a hyperexcitable focus with spontaneous recurrent seizures ### Clinical Features of HS-Associated TLE - **Febrile seizures in childhood** are a common antecedent (up to 50% of cases) - **Drug-resistant epilepsy** in 60–70% of patients - **Mesial temporal sclerosis pattern:** seizures typically originate from the medial temporal lobe - **Age of onset:** typically 10–20 years, with progressive seizure frequency ### Imaging Findings | Feature | Hippocampal Sclerosis | Other TLE Lesions | |---------|----------------------|-------------------| | **MRI appearance** | T2/FLAIR hyperintensity, volume loss | Variable (mass effect, flow voids, heterogeneous signal) | | **Laterality** | Usually unilateral | Can be bilateral or multifocal | | **Seizure lateralization** | Concordant with imaging in >90% | May be discordant | | **Surgical outcome** | Excellent (70–80% seizure-free) | Variable depending on lesion type | **High-Yield:** Hippocampal sclerosis is the **single most common cause of drug-resistant temporal lobe epilepsy** and the best predictor of good surgical outcome after anterior temporal lobe resection. **Clinical Pearl:** Patients with HS often have a characteristic history of febrile seizures in childhood followed by a symptom-free interval ("latent period") of years before the onset of spontaneous recurrent seizures in adolescence or early adulthood. [cite:Harrison 21e Ch 369]