The use of SPECT and PET in routine clinical practice in epilepsy

Abstract

The aim of this article is to give a subjective review of the usefulness of single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging in clinical practice in epilepsy for 2007. Both ictal perfusion SPECT and interictal fluorodeoxyglucose PET can provide new information in the presurgical evaluation of intractable partial epilepsy. These functional imaging modalities reflect dynamic seizure-related changes in cerebral cellular functions. Although asymmetry of fluorodeoxyglucose PET metabolism has been useful to localize the epileptic temporal lobe, which tends to be more hypometabolic than the contralateral one, both frontal lobes are more hypometabolic than the epileptic temporal lobe, and may represent a region of 'surround inhibition'. Due to its low temporal resolution, ictal perfusion SPECT hyperperfusion patterns often contain both the ictal onset zone and propagation pathways. These patterns often have a multilobulated 'hourglass' appearance. The largest and most intense hyperperfusion cluster often represents ictal propagation, and does not always need to be resected in order to render a patient seizure free. Optimized interictal FDG-PET and ictal perfusion SPECT as part of a multimodality imaging platform will be important tools to better understand the neurobiology of epilepsy and to better define the epileptogenic, ictal onset, functional deficit and surround inhibition zones in refractory partial epilepsy.