Abstracts

Rationale: Focal cortical dysplasia (FCD) is a potentially surgically correctable cause of refractory epilepsy in children. Magnetic resonance imaging (MRI) remains a powerful first-line tool in the identification of FCDs. Despite the recent advances in MRI techniques, it fails to reveal any apparent abnormality in approximately 20% of the patients with refractory epilepsy. In patients with a normal MRI, more sensitive techniques such as fluorodeoxyglucose positron-emission tomography (FDG-PET) can be useful in finding the abnormality. In children with refractory epilepsy and a normal brain MRI, little information is available regarding the role of FDG-PET in identifying subtle FCDs; especially, those involving the base of a sulcus. Methods: Fifty nine patients with surgically proven FCD at Children’s National Medical Center, between the years 2011-2017, were analyzed retrospectively. We identified seven patients with a normal brain MRI in whom a FDG-PET scan identified a FCD. The database was queried for demographics, MRI, FDG-PET, EEG, complications, Engel outcome, and pathology.  Results: Seven patients were identified with age of seizure onset ranging from 8 months to 13 years (3 males and 4 females). Age at surgery ranged from 5 years - 15 years.  Majority had focal seizures although one patient had atonic seizures as well. Preoperative seizure frequency ranged from 0.03-25 seizures per day. Number of AEDs tried prior to surgery ranged from 4-9. Brain MRI was normal in all cases and the FDG-PET identified focal hypometabolism raising the suspicion for a FCD. In four cases, ictal and interictal scalp EEG were concordant with the area identified on FDG-PET and no further invasive EEG monitoring was considered necessary whereas in three cases invasive EEG monitoring was done with placement of subdural electrodes. Locations of the FCDs were at the parietal (3 patients), frontal (2 patients) and temporal (2 patients) regions. A majority, 5 out of the 7 patients, had bottom of the sulcus or deep sulcal FCD. Type IIa was the commonest type of FCD identified on histopathology in 3 patients, type Ia (2 patients), type IIb (1 patient) and type IIId (1 patient). Four had Engel I outcome irrespective of the type of FCD.  Engel IV outcome was seen in one patient with FCD type IIId but it also had features of encephalitis. Duration of follow-up has ranged from 1-5 years. The number of post-operative AEDs have ranged from 0-2. Post-operative complications were not reported in any cases.  Conclusions: This observational study with a small sample size signifies that a normal brain MRI does not rule out the presence of a subtle FCD in children with medically refractory epilepsy. MRI often misses bottom of the sulcus/deep sulcal FCDs as was seen in the majority of our patients. Persistent evaluation in the pediatric age group with the use of FDG-PET can identify FCDs which can be surgically resected with good outcomes.  Funding: None