T2 Relaxometry Can Lateralize Mesial Temporal Lobe Epilepsy in Patients with Normal MRI

Abstract

In unselected patients with intractable temporal lobe epilepsy (TLE), approximately 15% do not have detectable hippocampal atrophy on MRI. The purpose of this study was to evaluate whether T2 relaxometry can identify hippocampal pathology and lateralize the epileptic focus in patients with intractable TLE, who do not demonstrate hippocampal atrophy on volumetric MRI (MRIV). We selected 14 patients with unilateral TLE who had unilateral atrophy and 11 patients with unilateral TLE who had no evidence of atrophy on MRIV. Images were acquired on a 1.5 T MR scan using a dual echo sequence with 23 contiguous oblique coronal slices in all patients and in 14 healthy subjects. Fitting a single exponential decay equation to the imaging data generated T2 maps. Averages of six slices containing the head, body, and tail of the hippocampus were used to calculate hippocampal T2 relaxation times (HT2). The epileptic focus was defined by history, video-EEG, and surgical response. All TLE patients with hippocampal atrophy and 9/11 (82%) patients with normal MRI had abnormally high HT2 ipsilateral to the epileptic focus. Bilateral abnormal HT2 were found in 6/14 (43%) of patients with unilateral hippocampal atrophy and 2/11 (18%) of patients with normal MRI. However, this increase was always greater ipsilateral to the epileptic focus. Qualitative hippocampal pathology showed gliosis and neuronal loss in 10/14 operated patients with hippocampal atrophy on MRIV and in 5/7 operated patients with normal MRI. In conclusion, hippocampal T2 mapping provides evidence of hippocampal damage in the majority of patients with intractable TLE who have no evidence of atrophy on MRI and can correctly lateralize the epileptic focus in most patients.

Quantitative relaxometry and diffusion MRI for lateralization in MTS and non-MTS temporal lobe epilepsy

“…In patients with normal conventional MRI (non-MTS TLE) findings from quantitative MRI have been more subtle than in MTS patients and less consistent, suggesting that non-MTS TLE is a distinct and possibly more heterogeneous entity than MTS. Previous relaxometry findings have shown increased T2 in the ipsilateral hippocampus (Bernasconi et al, 2000) and the ipsilateral temporal lobe (Mueller et al, 2007), with more pronounced differences in MTS patients. Quantitative investigation of longitudinal relaxation, or T1, known to be related to brain microstructure and myelination, could also contribute to the changes seen in T2-weighted images, however this has not yet been studied in the context of TLE.…”

3T MRI Quantification of Hippocampal Volume and Signal in Mesial Temporal Lobe Epilepsy Improves Detection of Hippocampal Sclerosis

“…2,8 Equally, the quantification of hippocampal T2 signal, especially with relaxometry, can improve the MR imaging diagnosis of HS. 9,10 Both volume and hippocampal signal quantification measurements have good correlation with histopathologic findings of HS. 4 Currently, these techniques are considered reliable and reproducible for the detection of hippocampal pathology.…”

Registration of in-vivo to ex-vivo MRI of surgically resected specimens: A pipeline for histology to in-vivo registration

“…Current clinical magnetic resonance imaging (MRI) protocols lack sensitivity, as more than 30% of patients have no evidence of brain lesions (Sylaja et al, 2004). Quantitative techniques such as diffusion tensor imaging (DTI), relaxometry mapping, voxel-based morphometry, and cortical thickness analysis have demonstrated increased sensitivity in lesion detection over routine or clinical MRI protocols (Bernasconi et al, 2000(Bernasconi et al, , 2004Bernhardt et al, 2009). These techniques have the potential to better delineate the epileptogenic zone and thus improve surgical outcomes, however, validation is currently needed to investigate and describe histopathological correlates of these imaging techniques (Eriksson et al, 2007;Howe et al, 2010).…”