Abstracts

Rationale: Seizures can be followed by transient neuological impairments (e.g., Todd’s paresis). Several case reports of post-ictal hypoperfusion exist, dating back to the work of Penfield and Jasper. More recently, prolonged post-ictal hypoperfusion and hypoxemia (lasting up to 1 hour) has been demonstrated at the seizure focus in rats (Teskey GC, unpublished observations). Thus, our objective was to determine whether post-ictal vascular changes can be demonstrated in humans and whether they could assist in localizing the seizure onset zone.Methods: Continuous tissue pO2 measurements were obtained in 5 patients with refractory focal epilepsy undergoing intracranial video-EEG monitoring (VEM) by placing an intracranial O2 sensing probe at or near the presumed seizure focus. Arterial spin labelling (ASL) MR images were obtained at 3 Tesla in a separate group of 16 patients with refractory focal epilepsy undergoing scalp VEM within 90 minutes of seizure termination. Baseline ASL scans were also obtained for comparison when patients were seizure-free for at least 24 hours.Results: Prolonged post-ictal pO2 reductions of at least 10 mm Hg, lasting up to 35 minutes were seen in both patients in whom the O2 probe was placed adjacent to the seizure focus (hippocampus in both cases, Figure 1). In the remaining three patients, the probe was placed distant from the seizure focus (>5 cm) and post-ictal hypoperfusion was seen for <5 minutes. ASL scans were obtained 45-90 minutes following seizure termination and focal post-ictal hypoperfusion was seen in 12/16 subjects, being localized to the presumed seizure focus in 10 patients and the ipsilateral hemisphere in 2 (Figure 2).Conclusions: Prolonged post-ictal pO2 and blood flow changes can be measured in humans. Post-ictal pO2 reductions can last up to 35 min and are more apparent near the seizure focus. Prolonged focal post-ictal hypoperfusion can be seen using ASL MR imaging in the majority of patients and they localize to the presumed seizure focus in most cases. Thus, prolonged post-ictal vascular changes may underlie post-ictal neurological deficits and may contribute to interictal neurocognitive deficits experienced by patients with epilepsy. In addition, post-ictal vascular imaging may be a potentially useful tool to assist in localizing the seizure onset zone.