MR detection of hippocampal disease in epilepsy: factors influencing T2 relaxation time.

PURPOSE To assess the reproducibility and stability of hippocampal T2 relaxation times and examine the effects of patients' age, seizures, and duration of epilepsy on this measure. METHODS Hippocampal T2 relaxation times were measured in 63 patients with chronic epilepsy (55 with partial and 8 with idiopathic generalized seizures) using a Carr-Purcell-Meiboom-Gill sequence, echo times 22 to 262 millisecond, on a 1.5-T clinical MR imaging system. Twenty-three patients on stable medication regimens underwent repeated T2 relaxometry after an interval of between 115 and 331 days. In 4 patients with partial seizures, hippocampal T2 relaxation times were measured interictally and again within 45 minutes of seizures. RESULTS In the 55 patients with partial epilepsy, hippocampal T2 relaxation times did not correlate with seizure frequency, duration of epilepsy, or age, but they were significantly more abnormal in those patients with a history of prolonged (more than 30 minutes) early childhood seizures than in those without. Eight patients with idiopathic generalized epilepsy had normal MR and hippocampal T2 relaxation times. In the 23 patients who underwent repeated T2 relaxometry there was no evidence of qualitative changes in T2-weighted images of the hippocampi or systematic changes of hippocampal T2 relaxation times with time. In 4 patients recent complex partial or secondary generalized seizures did not acutely alter hippocampal T2 relaxation times. CONCLUSION Hippocampal T2 relaxation time is a precise, reliable, stable, noninvasive measurement sensitive to hippocampal disease. These results do not suggest progression of hippocampal disease in patients with intractable partial seizures during periods of up to 331 days.