Quantitative magnetic resonance imaging in consecutive patients evaluated for surgical treatment of temporal lobe epilepsy

We present the results of quantitative Magnetic Resonance Imaging (MRI) in 55 consecutively referred patients with clinical evidence of temporal lobe epilepsy (TLE). The Cavalieri method was used in combination with point cou nting to provide unbiased estimates of the volume of the left and right hip pocampus, amygdala, temporal lobe, lateral ventricles and cerebral hemisphe re, and pixel by pixel maps of the T2 relaxation time were computed for bot h central and anterior sections of the hippocampus. The 99th centiles of hi ppocampal volume, hippocampal volume asymmetry and T2 relaxation times in 2 0 control subjects provided limits which identified the presence of MTS. Th e results of the quantitative MRT were compared with the results of convent ional diagnostic MRT, foramen ovale (FO) recording and the WADA test. Thirt y-one patients were found to have unilateral MTS (17 left and 14 right) and 7 bilateral MTS. No evidence of MTS was detected in 16 patients. Of the 31 patients diagnosed with unilateral MTS on the basis of hippocampaI volume and T2 measurement, 74% and 77% would respectively have received the same d iagnosis on the basis of hippocampal volume and T2 measurements alone. In c omparison to FO recording, quantitative MRI has a sensitivity of 55% and a specificity of 86%, while conventional diagnostic MRI has a sensitivity of 42% and a specificity of 80% for detection of MTS. Unilateral abnormalities were detected by FO recording in 30% cent of patients who appeared normal on quantitative MRI. WADA. test results were available for 40 patients. The findings were consistent with quantitative MRI showing reduced memory func tion ipsilateral to unilateral MTS in 18 patients, but reduced memory funct ion contralateral to unilateral MTS in two patients, and reduced memory fun ction without MR abnormality in seven patients. WADA testing revealed unila teral memory impairments where MRI found bilateral pathology in 4 patients and in 4 patients in whom quantitative MRI detected unilateral MTS there wa s no evidence of reduced memory during WADA testing of the corresponding ce rebral hemisphere. In the patients with unilateral right MTS a highly signi ficant negative correlation (p = 0.0003) was observed between age of onset and the volume of the contralateral temporal lobe. Quantitative MR imaging of the hippocampus (i.e. volume and T2 measurement) is preferable to conventional radiological reporting for providing objecti ve evidence of the presence of MTS on which to base the referral of patient s for surgery, and since it has associated morbidity FO recording is now on ly being used in selected patients. Furthermore, stereology provides a conv enient method for estimating the volume of other brain structures, which is relevant to obtaining a better understanding of the effects of laterality and age of onset of TLE. (C) 2001 Elsevier Science Inc. All rights reserved .