Quantitative hippocampal MRI and intractable temporal lobe epilepsy

Objectives: To evaluate and compare T(2) relaxometry and volumetrics of hippocampus in the presurgical evaluation of patients with intractable temporal lobe epilepsy (TLE), and to correlate these quantitative MRI measures with the pathology of the resected hippocampus. Patients; Forty patients with intractable TLE who underwent presurgical evaluation and subsequent temporal lobe surgery. Main outcome measures: Hippocampal T(2) (HCT(2)), volumes of hippocampi and hippocampal volume ratio (HCVR) (volume of hippocampus with higher HCT(2) divided by volume of hippocampus with lower HCT(2)), and qualitative pathology. Results: Thirty-two patients had hippocampal sclerosis, three patients had end-folium sclerosis, one patient had amygdala sclerosis, and four patients had a foreign tissue lesion in the temporal lobe. HCT(2) ratio (R/L) correlated inversely with the ratio of hippocampal volumes (R/L) (r = -0.91; p < 0.0001). A high T(2) signal in an atrophic hippocampus was characteristic of hippocampal sclerosis. All patients with hippocampal sclerosis had an HCVR below control values, and only one of these had an HCT(2) in the normal range. HCVR produced one false-positive result. The patients with end-folium sclerosis had normal HCT(2) and HCVR. The patient with amygdala sclerosis had a normal hippocampus on qualitative and quantitative assessment. Of the four patients with a lesion, one had a mildly increased HCT(2) and one had mild volume asymmetry. Hippocampal volume asymmetry could be reliably detected on visual inspection of the MRI with an HCVR of 0.85 or less, and an increase of HCT(2) with a T(2) of 115 msec or higher. Conclusion: Quantitative MRI combining HCT(2) and HCVR is a reliable method for diagnosing hippocampal sclerosis noninvasively. End-folium sclerosis and amygdala sclerosis should be considered in patients with intractable TLE and negative findings on MRI studies, including quantitative measures of the hippocampus.