Seizure onset zone localization using postictal hypoperfusion detected by arterial spin labelling MRI

Abstract

Neurological dysfunction following epileptic seizures is a well-recognized phenomenon. Several potential mechanisms have been suggested to explain postictal dysfunction, with alteration in cerebral blood flow being one possibility. These vascular disturbances may be long lasting and localized to brain areas involved in seizure generation and propagation, as supported by both animal and human studies. Therefore, measuring perfusion changes in the postictal period may help localize the seizure onset zone. Arterial spin labelling is a non-invasive, rapid and reproducible magnetic resonance imaging technique that measures cerebral perfusion. To this end, we measured postictal perfusion in patients with drug resistant focal epilepsy who were admitted to our seizure-monitoring unit for presurgical evaluation. Twenty-one patients were prospectively recruited and underwent arterial spin labelling scanning within 90 min of a habitual seizure. Patients also underwent a similar scan in the interictal period, after they were seizure-free for at least 24 h. The acquired scans were subtracted to identify the areas of significant postictal hypoperfusion. The location of the maximal hypoperfusion was compared to the presumed seizure onset zone to assess for concordance. Also, the localizing value of this technique was compared to other structural and functional imaging modalities. Postictal perfusion reductions of >15 units (ml/100 g/l) were seen in 15/21 patients (71.4%). In 12/15 (80%) of these patients, the location of the hypoperfusion was partially or fully concordant with the location of the presumed seizure onset zone. This technique compared favourably to other neuroimaging modalities, being similar or superior to structural magnetic resonance imaging in 52% of cases, ictal single-photon emission computed tomography in 60% of cases and interictal positron emission tomography in 71% of cases. Better arterial spin labelling results were obtained in patients in whom the seizure onset zone was discernible based on non-invasive data. Thus, this technique is a safe, non-invasive and relatively inexpensive tool to detect postictal hypoperfusion that may provide useful data to localize the seizure onset zone. This technique may be incorporated into the battery of conventional investigations for presurgical evaluation of patients with drug resistant focal epilepsy.

Diagnostic usefulness of arterial spin labeling in MR negative children with new onset seizures

“…In a human study from the same group, cerebral perfusion was measured using ASL subtraction technique, and hypoperfusion was seen in 15/21 (71.4%) patients, with 12/15 (80%) showing concordance with the location of the presumed seizure onset zone, within 60 min of seizure termination. However, most patients who had late postictal ASL scans (> 60 min) showed no significant hypoperfusion [17]. In another study, the overall accuracy was higher in patients whose ASL perfusion were acquired at ≤ 3 days compared to > 3 days.…”

“…In the previous literature, the sensitivity of ictal SPECT was reported to vary from 81 to 90% and that of PET from 30 to 80%, depending on the lobes and age. 4; 17 One study reported that postictal perfusion change on ASL offered similar or better localization compared to ictal SPECT in 60% of cases (9/15) and interictal PET in 71% of cases [17]. In another study, ASL showed a very good concordance with PET (k = 0.84) and a fair concordance with subtracted ictal SPECT co-registered with MRI (SISCOM) (k = 0.28) [18].…”

Resolving the Micro-Macro Disconnect to Address Core Features of Seizure Networks

“…Like ictal hyperperfusion, the expression of COX-2 in excitatory neurons could be informative of the underlying excitatory networks recruited by seizures. Use of non-invasive arterial spin labeling (ASL) MRI to map blood flow 45-60 min after patients' seizures demonstrated that this method had similar or superior localization value to other commonly used imaging modalities (Gaxiola-Valdez et al, 2017). One major advantage to consider is that this approach provides a time window of approximately 1 h to detect postictal hypoperfusion, which is sufficient time to transfer a patient to the imaging facility to capture a scan.…”

Seizures cause sustained microvascular constriction associated with astrocytic and vascular smooth muscle Ca2+ recruitment

“…systematically investigated local oxygen levels and blood flow following evoked and self-generated seizures in behaving rodents and discovered a severe hypoxic event (pO 2 < 10 mmHg) that lasted over an hour. This phenomenon was the result of blood hypoperfusion and it generalized to people with epilepsy (Farrell et al, 2016;Gaxiola-Valdez et al, 2017;Li et al, 2019). Furthermore, Farrell et al, (2016) demonstrated that brain region-specific postictal memory and behavioral impairments were the consequence of this hypoperfusion/hypoxic event.…”