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.

Hippocampal atrophy, which is a component of hippocampal sclerosis and recognized commonly in human intractable epilepsy, is controversial in canine epilepsy. We examined the hippocampal volume in 58 epileptic dogs and 35 control dogs using magnetic resonance (MR) images, and calculated the relative hippocampal volume asymmetry of the right and left hippocampus. Subjectively, there were visible MR imaging abnormalities in seven of the 58 epileptic dogs (12%). The hippocampel volume asymmetric ratio of epileptic dogs (5.84±4.47%) was significantly greater than that of control dogs (1.62±0.88%). Using a cutoff threshold asymmetric ratio of 6% that is indicated in human epilepsy, 28 epileptic dogs (48%) were characterized as having unilateral hippocampus atrophy. The hippocampal volume asymmetry ratio cannot be used to detect bilateral atrophy. In conclusion, although less frequent than that observed in human epilepsy patients, hippocampal atrophy may occur in canine epilepsy.