A grading system for hippocampal sclerosis based on the degree of hippocampal mossy fiber sprouting

In patients suffering from temporal lobe epilepsy (TLE) a highly variable d egree of hippocampal sclerosis (HS) can be observed. For standard neuropath ological evaluation after hippocampal resection, neuronal cell loss in the hippocampal subareas is assessed (Wyler score 0-4) [Wyler et al. (1992) J E pilepsy 5: 220-225]. Other marked morphological changes in the sclerotic hi ppocampus are gliosis and loss of mossy fibers in the hilus and mossy fiber sprouting in the supragranular layer. In this study we quantified changes in mossy fiber density using Timm's stain in resected hippocampal tissue fr om patients with various degrees of sclerosis. We found that tissue specime ns from patients without sclerosis (WO) show almost no mossy fiber sproutin g. Patients with moderate sclerosis show sprouting without fiber loss in th e hilus, whereas specimens from patients with severe sclerosis show sprouti ng as well as fiber loss in the hilus. Thus, analysis of mossy fiber abunda nce in hilus and supragranular layer by the rapid and simple Timm's stain i s a sensitive measure for hippocampal sclerosis. It provides a reliable rap id tool for neuropathological evaluation, even if the tissue only contains dentate gyrus due to the sectioning procedure.