MORPHOLOGICAL AND FUNCTIONAL NEURO-IMAGIN G IN REFRACTORY PARTIAL EPILEPSIES OF ADULTS

This article reviews literature on morphological and functional neuro- imaging data in refractory partial epilepsies of adults including Magn etic Resonance Imaging (MRI), Single Photon Emission Computerised Tomo graphy (SPECT) and Positron Emission Tomography (PET). Except for MRI, which is of unquestionable utility in the diagnosis of epileptogenic lesions, most of these investigations are justified only in the contex t of pre-operative evaluation of candidates to functional neurosurgery . In terms of interpretation the key issue is that of the relation bet ween the images and the epileptogenic process itself. The specific uti lity of available techniques is as follows: MRI, in its present state of development, reveals a morphological abnormality in more than 80 % of the cases previously considered as cryptogenic on the basis of X ra y Computerised Tomography. However, hippocampal atrophy, which has a q uestionable relation with temporal lobe seizures, represents two third s of abnormal images. Functional MRI and MR spectroscopy represent pot ential alternatives respectively to Wada test and interictal SPECT or PET. Ictal blood flow studies during video-LEG monitoring represent th e major application of SPECT; showing a focal increase of blood flow i n more than 90 % of cases. Interictal SPECT is less informative, but n ecessary for interpreting ictal images. F-18-Deoxyglucose (FDG) PET sh ows a focal interictal hypometabolism in nearly 90 % of patients with refractory temporal lobe epilepsy. The incidence of interictal hypomet abolism is less, though more than 50 %, in the other types of partial epilepsies. For diagnostic purpose PET studies of benzodiazepine (BZD) - receptors with C-11-Flumazenil are more widely used than those of op iate or mucarinic receptors. The reduced density of BZD receptors is l ikely to reflect neuronal loss, whereas interictal glucose hypometabol ism reflects both the lesional process and secondary deactivation of p erilesional areas due to anatomical or functional deafferentation.