Abstracts

Malformations of cortical development (MCD) are an important cause of refractory focal epilepsy.The published prevalence of MCD in refractory epilepsy ranges from 8-12%; these studies were however done in 1.5T MRI scanners, before 3T MRI, newer MRI sequences and postprocessing of MRI images. The prevalence of MCD may thus have been underestimated. PET was also not used as an ancillary tool.
The prevalence of MCD in refractory focal epilepsy in Singapore is unknown; we aimed to determine this using 3T MRI and PET., Patients aged 16-65 years with medically refractory focal epilepsy were recruited. They were classified as refractory if they had tried and failed at least 2 antiepileptic drugs at maximum tolerated doses, and if they still had 2 or more seizures a month for the past 2 years.
MRI was performed using a 3T Phillips MRI scanner using a dedicated epilepsy protocol. Conventional T2 and FLAIR sequences were performed, with coronal sections orthogonal to the long axis of the hippocampus. Optimised 3D magnetisation-prepared rapid acquisition with a gradient echo (MPRAGE) sequences with an isotropic whole-brain sub-millimetre acquisition (0.9x0.9x0.9mm[sup3]) using parallel imaging (SENSE) technology was also performed. SENSE MPRAGE (axial) datasets in high resolution were acquired and reformatted into sagittal, coronal and oblique planes as needed.
MRIs were independently reviewed by 2 neuroradiologists experienced in epilepsy neuroimaging; they were provided only information about semiology and EEG, and blinded to all other data, including prior neuroimaging. Disagreement was resolved by consensus.
If the MRI was interpreted as normal, a 18FDG PET scan was performed. Areas of hypometabolism were re-examined on the MRI using multiplanar reformatting (MPR)., Forty patients (22 female) were recruited; mean age 42.1[plusmn]9.6 years. The duration of epilepsy was 8.2[plusmn]6.2 years, seizure frequency was 3.1[plusmn]2.8 per month. Mean number of antiepileptic drugs trialled was 2.9[plusmn]2.7.
MRI identified a lesion in 30/40 patients initially. PET was performed for 10/40 patients. MRI MPR after review of PET data allowed identification of a lesion in 1 additional patient.
Of the 31 patients with a lesion after MRI and PET scans, 14 showed hippocampal sclerosis (12 unilateral, 2 bilateral), 8 showed gliosis, 3 showed benign tumours (1 ganglioglioma, 1 glioma, 1 DNET). Six were found to have MCD - 2 polymicrogyria, 2 focal cortical dysplasia (FCD), 2 periventricular heterotopia. In 1 patient with subtle FCD this was identified only after PET and multiplanar reformatting was performed., MCD is not uncommon and was seen in 15% of our cohort. Combined MRI and PET imaging, using multiplanar reformatting, allows identification of MCD, especially subtle cortical dysplasia., (Supported by NMRC Singapore.)