Purpose or Case Report: 1. Review of structural and metabolic imaging findings across various classes of FCD based on recent ILAE classification.
2. Review of correlation between imaging findings and pathologic features in different FCD groups.
Methods & Materials: The review is based on retrospective evaluation of pediatric patients who underwent surgery for treatment of medical refractory epilepsy at our institution between 2000 and 2018. The inclusion criteria were presence of at least one pre-operative optimal quality MR imaging (1.5T or 3T) exam of brain dedicated to epilepsy evaluation and interictal FDG-PET brain study within past 1 year of surgery. Patients with presence of mMCD (mild malformation of cortical development) including microdysgenesis and neuronal heterotopia were also included. Patients with pathology proven isolated epileptogenic neoplastic lesions, isolated hippocampal sclerosis or nonspecific gliosis were excluded.
Results: The search of institutional radiology database showed 20 patients who met our criteria. 2 patients were excluded because of suboptimal imaging exam (either MRI or FDG-PET brain). Out of the 18 patients, no patients were noted under ILAE pathologic Class Ia, IIIb and IIIc. The ILAE class with most number of patients was IIIa (FCD with hippocampal sclerosis), MR imaging in all of them demonstrated hippocampal sclerosis but was negative or equivocal for FCD; the FDG-PET in this group appeared to correlate better with distribution of FCD on surgical pathology. No transmantle sign was noted in this pediatric population, although this could be due to small sample size. 2 patients had underlying tuberous sclerosis evident on MR imaging and showing diffuse hypometabolism reflecting global pathology. 2 patients had mMCD with unremarkable MRI exams and focal abnormalities on FDG-PET corresponding to area of pathology.
Conclusions: The use of information from both MRI and FDG-PET can help in identifying the epileptogenic zone better in FCD. The FDG-PET appears more sensitive than MRI in type I FCD. The structural imaging has higher specificity and can characterize FCD lesions of type II and III better.