Ratio Ictal SPECT Co-registered with MRI visualizes a greater extent of the ictal onset zone in focal refractory epilepsy

Abstract

Background: Until recently, the main non-invasive technique to evaluate the ictal onset zone has been Subtraction ictal SPECT coregistered with MRI (SISCOM). While SISCOM provides useful information about the ictal onset zone, the case we report herein suggests the possibility that multiple regions are involved in a more complex network 7 , whose identification can improve the patient’s prospects for resective epilepsy surgery. Case: The 23 year old right handed female case under discussion illustrates how Ratio Ictal SPECT coregistered with MRI (RISCOM) findings better guided the invasive evaluation with a more precise targeting of the subdural grids. Here, the concordance between the noninvasive technique (RISCOM) and the invasive evaluation (chronic electrocorticography) allowed a better determination of the seizure onset zone for resective epilepsy surgery. In turn, the resected tissue included a more extended area (orbitofrontal), which was not seen by SISCOM. Importantly, the case also allows for a better understanding of the relationship between the epileptogenic lesion and the ictal onset zone, and their role in the postsurgical outcome. The patient achieved seizure freedom (Engel 1A). Conclusion: A more accurate determination of the ictal onset zone by this novel noninvasive technique not only greatly impact in the postsurgical outcome of patients with focal refractory epilepsy. It may also indicate that the ictal onset zone can be the expression of interlobar connections that does not necessarily include the epileptogenic lesion of patients with malformations of cortical development.