Brain diffusion during hyperventilation: diffusion-weighted MR-monitoring in patients with temporal lobe epilepsy and in healthy volunteers

Hyperventilation (HV) can be used to provoke epileptiform activity and occasionally seizures in generalised and in focal epilepsies. Based on the hypothesis that HV might alter brain diffusion in the epileptogenic areas of patients with temporal lobe epilepsy (TLE), we examined these alterations using quantitative diffusion MR imaging (DI) in four patients with TLE and unilateral hippocampal sclerosis (TLE-HS) and six patients with TLE without hippocampal sclerosis (TLE-pure), and in 10 healthy volunteers. Brain diffusion was measured at baseline and immediately after 4 min of HV. In all patients with TLE HV was repeated two times, 4 min each, followed by subsequent DI. The apparent diffusion coefficient (ADC) was quantified in predefined regions of interest. In controls, the ADC did not differ between baseline and HV and between right and left side. Compared to controls TLE-HS patients showed significantly higher ADC at baseline in the hippocampus of the ictogenic side (111+/-13 vs. 87.5+/-4.26 x 10(-5) mm(2)/s, P=0.029). During HV ADC decreased significantly in the ictogenic hippocampus compared to controls (-17.3+/-7.1 vs. -3.34+/-8.7, P=0.004). In TLE-pure patients ADC of the ictogenic hippocampus was higher than in normals (99.3+/-14.2 vs. 87.5+/-4.26 x 10(-5) mm(2)/s, P=0.031) but there was no significant decrease during HV. Serial HV did not further enhance this decrease. No significant HV-induced changes were seen in other brain areas. In conclusion, our results show that HV can induce dynamic changes of brain diffusion in patients with sclerotic hippocampi but not in non-sclerotic hippocampi. These findings may be utilized for lateralisation of the epileptogenic hippocampus during presurgical evaluation of TLE.