Cause: long-standing temporal lobe epilepsy

Histo: marked neuronal loss + astrogliosis in hippocampal subfields CA1 + CA3 + CA4

Mechanism for excitotoxicity-induced neuronal death:

• seizures → excessive neuronal depolarization → overproduction of excitory amino acid neurotransmitters → excessive activation of N-methyl-D-aspartate receptors → unregulated entry of Ca²⁺→ neuronal swelling with cytotoxic edema

Location: uni- / bilateral; symmetric / asymmetric

• hippocampal atrophy + loss of internal architecture
• increased signal intensity on T2WI
• dilatation of temporal horn

Associated limbic system findings:

• ipsilateral atrophy of fornix (55%)
• ipsilateral atrophy of mamillary body (26%)

Associated extrahippocampal abnormalities:

• increased SI of anterior temporal lobe cortex (38%)
• cerebral hemiatrophy (1%)

Rx: amygdalohippocampectomy