Abstract
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Objectives: Periventricular Nodular Heterotopias (PNHs) are malformations of cortical development (MCD) related to neuronal migration disorders, frequently associated with drug-resistant epilepsy (DRE). A pivotal role of these lesions has been demonstrated in the pathogenesis of the epileptic activity, both close and at distance in the neocortex. Although magnetic resonance imaging (MRI) can clearly define the morphological features of PNHs, it still remains unclear whether the metabolic activity of these ectopic neurons may correlate with neurologic symptoms. Furthermore, it may be hypothesized that FDG PET findings can predict long-term outcome of patients affected by PNHs. The aims of our study were to compare the diagnostic performance of 18F-FDG PET/CT compared to MRI, to assess the metabolic activity of the epileptogenic foci and to evaluate the clinical and prognostic value of PET findings.
Methods: Fifteen patients (8 men and 7 women; age range, 23-52 years) diagnosed with PNHs-related DRE were retrospectively evaluated from a single-centre database. All underwent clinical evaluation, Stereo-Electroencephalogram (SEEG), 1.5T 3D-brain MRI and 18F-FDG brain PET/CT. PET images were superimposed on the patient-specific 3D-brain MRI to allow for a more accurate comparison. Metabolic activity was visually assessed and classified as normal (i.e. not significantly different from that of the surrounding structures), increased, reduced or absent. 1 to 19 months after neuroimaging, the patients underwent surgical intervention either with radiofrequency thermocoagulation only (11 of 15, 73.3%), conventional surgery only (1 of 15, 6.7%) or both (3 of 15, 20%). Outcome was assessed at 蠅8-month follow-up (median 28 months). A favorable outcome was defined as reduced rate of seizures (Engel outcome 1A,1B,1C and 2A) and/or therapy reduction.
Results: Four patients (26.7%) had unilateral PNHs localized in the right hemisphere, 3 unilateral in the left hemisphere and 8 (53.3%) had bilateral PNHs. MRI identified a total of 23 heterotopic sites. Of these, 10 (43.5%) showed on PET a normal metabolic activity, 8 (34.8%) were rated hypometabolic and in 5 (21.7%) FDG metabolism was absent. PET allowed to identify other metabolic alterations outside the heterotopias, correlating with neurological symptoms. Specifically, a hypometabolism has been observed on the anterior mesial temporal region in 8 patients (53.3%) and on posterior temporal region in 2 (13.3%). The complex PNH-associated cortical malformations showed invariably a normal metabolism. At follow-up, reduced rate of seizures was reported in 13 patients (86.7%), while therapy was reduced in 5 (33.3%). At univariate and multivariate analysis, the presence of hypometabolism or absent uptake in the heterotopic sites was significantly associated with a more favorable outcome (p=0.03).
Conclusion: Brain 18F-FDG PET/CT identified 13 of 23 heterotopic sites identified by MRI (56.5%, 8 hypometabolic and 5 with absent uptake). However, more metabolic alterations were detected, correlating with neurological symptoms. Furthermore, hypo- or absent metabolism on PET can predict a more favorable outcome. Brain FDG PET/CT provides important information on metabolic activity and allows to predict the outcome of surgical therapy. Research Support: N/A