CT perfusion measurement of postictal hypoperfusion: localization of the seizure onset zone and patterns of spread.

Abstract

Seizures are often followed by a period of transient neurological dysfunction and postictal alterations in cerebral blood flow may underlie these symptoms. Recent animal studies have shown reduced local cerebral blood flow at the seizure onset zone (SOZ) lasting approximately 1h following seizures. Using arterial spin labelling (ASL) MRI, we observed postictal hypoperfusion at the SOZ in 75% of patients. The clinical implementation of ASL as a tool to identify the SOZ is hampered by the limited availability of MRI on short notice. Computed tomography perfusion (CTP) also measures blood flow and may circumvent the logistical limitations of MRI. Thus, we aimed to measure the extent of postictal hypoperfusion using CTP. Fourteen adult patients with refractory focal epilepsy admitted for presurgical evaluation were prospectively recruited and underwent CTP scanning within 80min of a habitual seizure. Patients also underwent a baseline scan after they were seizure-free for > 24h. The acquired scans were qualitatively assessed by two reviewers by visual inspection and quantitatively assessed through a subtraction pipeline to identify areas of significant postictal hypoperfusion. Postictal blood flow reductions of > 15ml/100g-1/min-1 were seen in 12/13 patients using the quantitative method of analysis. In 10/12 patients, the location of the hypoperfusion was partially or fully concordant with the presumed SOZ. In all patients, additional areas of scattered hypoperfusion were seen in areas corresponding to seizure spread. CTP can reliably measure postictal hypoperfusion which is maximal at the presumed SOZ.