Objective The authors aimed to determine the ability of resting-state functional connectivity MRI (fcMRI) to lateralise/localise the epileptogenic zone in patients presenting with mesial temporal lobe epilepsy (MTLE) at the individual level.

Methods Basal functional connectivity (BFC) was evaluated in each hemisphere of 22 MTLE patients. 200 volumes were acquired using a single-shot GE-EPI sequence during a resting period of 10 min at 1.5 T. The signal time-course was extracted from 10 regions of interest (ROIs), five ROIs in each hemisphere, usually involved in epileptogenic networks of MTLE. Normalised correlation coefficients between pairs of ROIs signal time-courses were computed to reflect BFC. Based on normative BFC values obtained from 36 controls, the number of BFC decreases and increases were determined in each hemisphere for each patient.

Results BFC decreases were found bilaterally, although the number of decreased links was significantly higher in the epileptogenic side (p=0.025). Conversely, BFC increases were found almost exclusively in the contralateral lobe leading to a strong test effect for locating the non-epileptic lobe with a sensitivity of 64% and a specificity of 91% (p<0.001). The most frequently disconnected areas were the entorhinal cortex and the anterior hippocampus in the epileptic lobe, while contralateral BFC increases involved preferentially hippocampus and amygdala.

Conclusions This study demonstrates that the presence of BFC increases in the non-epileptic side was paradoxically the most specific marker of epileptogenic zone localisation, and suggests that a single resting-state fcMRI could be useful in the presurgical assessment of MTLE at an individual level.