Fluid-attenuated inversion recovery - Correlations of hippocampal cell densities with signal abnormalities

Background: Hippocampal sclerosis (HS) is characterized by hippocampal atro phy and increased signal on T2-weighted images and on fluid-attenuated inve rsion recovery (FLAIR) images. Objective: To quantitate cell loss and compa re it with signal abnormalities on FLAIR images. Methods: Thirty-one patien ts with temporal lobe resection, pathologically proven HS, and Engel class I and II outcome were included: 20 with HS only and 11 with HS associated w ith pathologically proven cortical dysplasia (dual pathology). The signal i ntensity on FLAIR was rated as present or absent in the hippocampus and cor related with the neuronal losses in the hippocampus. Results: FLAIR signal increases were present in 77% (24/31) of all patients studied. In patients with isolated HS, 90% (18/20) had ipsilateral signal increases, but in pati ents with dual pathology, only 55% (6/11; p < 0.02) showed FLAIR signal inc rease. Hippocampal cell losses were significantly higher in the isolated HS group. The average cell loss in patients with FLAIR signal abnormalities w as 64.8 +/- 8.0% as compared with only 32.7 +/- 5.1% in patients with no FL AIR signal abnormalities. There was a significant positive correlation betw een the presence of signal abnormality and average hippocampal cell loss in both pathologic groups. Conclusions: Ipsilateral FLAIR signal abnormalitie s occur in the majority of patients with isolated HS but are less frequent in those with dual pathology. The presence of increased FLAIR signal is cor related with higher hippocampal cell loss.