Brain Diffusion after Single Seizures
Hufnagel A, Weber J, Marks S, Ludwig T, De Greiff A, Leonhardt G, et al.;
Commented by , 24 Feb 2003
Background
Topographic localization of the epileptogenic zone is of great importance in the classification and treatment of epilepsy. In this regard EEG has physical limitations and emission tomography (SPECT or PET) does not provide sufficient information in post-or interictal examinations.
Ictal SPECT has been used for localization of epileptogenic activity, although restrained by logistic procedures (availability, preparation and injection of tracer). Interesting data has been reported using new MRI techniques such as MR spectroscopy (MRS), showing significant interictal reduction of the metabolic composition of the tissue (N-acetyl aspartate ratio) in the epileptogenic zone (M Guye et al., Epilepsia, 2002;43:1197-).
Diffusion-weighted MR imaging (DWI) measures diffusion of tissue water, and has successfully been implemented in stroke detecting acute ischemic lesions. Relevant DWI apparent diffusion changes (ADC) have been reported postictally in patients with epilepsy, and new imagers with high temporal and spatial resolution have facilitated its use in epilepsy.
Aim
To determine if localized dynamic alterations of brain diffusion during the immediate postictal state will be detectable by serial DWI and will correlate with the epileptogenic zone.
Methods
The study was prospective and included nine patients with temporal lobe epilepsy (TLE; n=5), temporal + extratemporal lobe epilepsy (TLE + ETE; n=2), and extratemporal lobe epilepsy (ETE; n=2). All patients had medically refractory epilepsy with complex partial seizures, simple partial seizures, and secondary generalized seizures.
All patients underwent complete presurgical evaluation including structural MRI, noninvasive interictal and ictal EEG monitoring, and neuropsychological evaluation. Additional interictal and postictal (2 – 210 min after seizure) high resolution DWI (pixel size 1,72 x 1,72 x 5 mm) was then performed.
Results
Interictal ADC was significantly (p<0,05) elevated in the ictogenic hippocampus in patients with TLE. In the postictal measurements, changes in ADC were seen as decreases by maximally 25-31%, most pronounced in the epileptogenic zone (n=2), generalized ADC changes after generalized seizures (n=1) or prolonged complex partial seizures (n=2), no major changes after short-lived seizures (n=3), and widespread bilateral ADC increases after a flumazenil-induced seizure (n=1).
Discussion
The study describes dynamic changes in cerebral diffusion caused by epileptogenic activity. In line with previous studies, an increase was found in the interictal ADC in epileptogenic tissue, which presumably is caused by increased extracellular space. ADC changes after single seizures were heterogeneous and may reflect phases of reactive hyperperfusion or reactive hyperpolarization.
These changes theoretically correspond with results of SPECT studies of ictal, post – and interictal changes in CBF. Although further studies are needed, the authors conclude that DWI has the potential of providing important in vivo information of pathophysiological processes with high temporal resolution in epilepsy, which can be obtained without any hazard to the patient.
Together with MRS and other MRI techniques, this will in time lead to more refined non-invasive diagnostic and pre-therapeutic evaluation in epilepsy.