Diagnostic techniques to detect the epileptogenic zone: Pathophysiological and presurgical analysis of epilepsy in dogs and cats

The use and availability of magnetic resonance imaging (MRI) and other neurosurgical devices is rapidly increasing in the field of veterinarian medicine. Coincident with these technological advances, there is an increased expectation to treat drug resistant epilepsy in dogs and cats by epilepsy surgery. However, the presurgical evaluation of epileptic animals, by using methodologies to detect the epileptogenic zone for example, have yet to become established in common practice. The epileptogenic zone, defined as the minimum amount of cortex to produce seizure freedom, consists of five conceptual cortical abnormal 'zones': symptomatogenic, irritative, seizure-onset, structurally abnormal (epileptogenic lesion) and functional deficit. These zones can now be detected by suitable modalities including ictal video monitoring, interictal non-invasive or invasive electroencephalography (EEG), ictal video-EEG, magnetoencephalography, structural and functional MRIs, or nuclear imaging. These diagnostic techniques are essential for selecting both appropriate patients and surgical techniques, and are also important in understanding the pathophysiology of epilepsy. This review describes the diagnostic techniques available for detecting each abnormal zone while considering the current veterinary status to realise future surgery for canine and feline epilepsy.