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Introduction: Single photon emission computed tomography (SPECT) imaging regional cerebral blood flow (rCBF) can help localize the seizure focus in partial epilepsies during presurgical evaluation. Few studies have explored the possible relationship between preoperative SPECT and underlying pathology, or any relationship to postsurgical outcome. Study group: Thirty-five children with medically intractable epilepsy undergoing resective surgery between the ages of 11 months and 18 years had presurgical ictal and interictal rCBF and post surgery follow up of 3–6 years. Results: Pathological examination revealed 13 to have hippocampal sclerosis (HS): of these 11 had relatively low interictal rCBF perfusion on the side of seizure onset, and eight had hyperfusion ictally. Eight children had morphological evidence of cortical dysplasia: all had a localizing ictal rCBF concordant with the area resected whereas only six demonstrated localized reduction in perfusion on interictal rCBF. All three patients with Rasmussens encephalitis had informative rCBF scans, concordant with the seizure focus. However, infarct, tumours and nonspecific pathology demonstrated poor localization of the seizure focus. No SPECT parameter correlated independently with outcome, although overall the HS group had the best outcome, particularly those with localizing ictal SPECT. Comment: Ictal SPECT appears predictive of underlying cortical dysplasia. Although in this small group of HS in children, ictal SPECT added little to interictal SPECT for seizure localization, it may be useful in the prediction of outcome. SPECT adds little to the evaluation of children being considered for hemispherectomy over and above the abnormalities detectable on MRI scan. [ABSTRACT FROM AUTHOR]