Abstracts

Rationale: In patients with medically refractory focal epilepsy and have normal MRI, high-resolution dedicated MRI may identify cryptic lesions. The aim of this study was to assess the improvement in detecting a lesion using additional high-resolution dedicated 3T MRI in children with medically refractory focal epilepsy who has initial normal 3T MRI with epilepsy protocol. Methods: Children who have had resective epilepsy surgery and had 3T epilepsy protocol MRI were identified. Inclusion criteria included those who had suspected focal cortical dysplasia (FCD) or normal MRI on 3T epilepsy protocol. Exclusion criteria include those with other diagnoses on 3T epilepsy protocol MRI including tumor, hippocampal sclerosis, tuberous sclerosis and Rasmussen encephalitis. Those who had normal MRI on 3T epilepsy protocol underwent additional high-resolution dedicated imaging through the area of concern, guided by video EEG, magnetoencephlaography and FDG-PET data. Clinical data collected include age at surgery, histology, and surgical outcomes. Results: 101 patients with mean age of 9.6 years (SD=5.3 years), consisting of 54 (54%) males were included in the study. On the initial 3T epilepsy protocol MRI, 57 (56%) patients had abnormal MRI which was suspected to be FCD, and 44 (44%) patients had normal MRI. 29/44 (29%) patients who previously had normal MRI on 3T epilepsy protocol had a lesion identified on repeat dedicated MRI. 21/29 (72%) patients with normal MRI on initial 3T epilepsy protocol and subsequently had a lesion identified on additional high-resolution dedicated 3T MRI were seizure free; 34/57 (60%) with abnormal MRI on 3T epilepsy protocol were seizure free; and 9/15 (60%) with normal MRI on 3T epilepsy protocol and additional high-resolution dedicated 3T MRI were seizure free at one-year follow-up. The sensitivity and specificity of 3T epilepsy protocol in detecting seizure free outcome were 53% (95%CI: 40%-66%) and 37% (95%CI: 22%-55%) respectively. The addition of high-resolution dedicated 3T MRI change the sensitivity and specificity of detecting seizure free outcome to 86% (95%CI: 75%- 93%) and 16% (95% CI: 6%-32%) respectively. Conclusions: Our results indicate that patients with focal epilepsy and had initial negative 3T MRI with epilepsy protocol, additional imaging with high-resolution dedicated 3T MRI may aid identification of an underlying lesion. Funding: N/A