Mini-Review: Morphological changes in the human epileptogenic hippocampus

Abstract

The availability of surgical tissue from epilepsy patients and the development of different animal models have increased our knowledge about the morphological changes in the epileptogenic brain. In this review we focus on the main morphopathological changes in the hippocampus from patients with temporal lobe epilepsy. The pathological substrate most frequently found in patients, suffering from temporal lobe epilepsy is hippocampal sclerosis. The sclerotic hippocampus is characterized by neuronal degeneration, astrogliosis, and granule cell dispersion. Even temporal lobe epilepsy patients with a non-sclerotic hippocampus suffer from neuronal cell loss. Another important hallmark of the sclerotic hippocampus is the presence of mossy fibre sprouts in the supragranular region of the dentate gyrus. This so called “mossy fibre” sprouting was only observed in the sclerotic hippocampus, and corresponded to the degree of hippocampal sclerosis. Moreover, the demonstration of actively sprouting mossy fibres in the sclerotic hippocampus, indicates that the process of mossy fibre sprouting is still an active, on-going process in the sclerotic hippocampus, even though these patients have suffered from seizures for many years. This active mossy fibre sprouting could potentially further aggravate the process of neuronal degeneration and astrogliosis. Therefore, it seems important to surgically remove the sclerotic hippocampal tissue in patients with temporal lobe epilepsy as early as possible.