What pathological change characterizes hippocampal sclerosis in mesial temporal lobe epilepsy?

• A. Neuronal loss with gliosis in mesial temporal structures
• B. Demyelination of the corpus callosum
• C. Acute neutrophilic infiltration
• D. Vascular amyloid deposition

Answer: (A)

Hippocampal sclerosis in mesial temporal lobe epilepsy is defined by selective neuronal loss with reactive gliosis in the hippocampus and related mesial temporal structures. The loss is most pronounced in the hippocampal subfields, especially CA1 and CA3, and often involves the dentate gyrus with granule cell dispersion and gliotic scarring from astrocyte proliferation. This pattern underlies the chronic seizures of MTLE and is commonly seen in surgical specimens from patients with refractory epilepsy; imaging often shows hippocampal atrophy with T2 hyperintensity reflecting the sclerosis.

Other processes described do not fit this pattern: demyelination of the corpus callosum is characteristic of multiple sclerosis; acute neutrophilic infiltration suggests an acute infectious process; vascular amyloid deposition occurs in cerebral amyloid angiopathy or Alzheimer disease and is not the defining pathology of hippocampal sclerosis in MTLE.