Abstracts

In neonates with persistent seizures, positron emission tomography (PET) studies of brain glucose metabolism assists in identifying the epileptic focus and areas of cerebral dysgenesis. However, difficulty in transporting sick infants between nursery and PET facility is a major obstacle in accomplishing the PET studies. Furthermore, the spatial resolution of clinical PET scanners is not ideal for imaging the small brains of newborns. Recent advances in PET detector technology have led to a new generation of microPET scanners designed for imaging small animal brains. We have modified the Focus 220 microPET scanner (Concorde Microsystems, Knoxville, TN) for human use and placed this scanner in our intensive care nursery to avoid the problem of transporting sick babies. With a patient opening of 22 cm and an axial field-of-view of 8 cm, this scanner can also be used in larger infants [lt]15 kg body weight. To date, we have scanned 22 babies (34 weeks gestational age to 8 months postnatal) with neonatal seizures. All infants were bundled with blankets and fastened to the bed with velcro straps. Vital signs were monitored. PET studies of cerebral glucose metabolism (using 2-deoxy-2[¹⁸F]fluoro-D-glucose) and GABA[sub]A[/sub] receptor binding (using ¹¹C-flumazenil) documented the high spatial resolution ([lt]2mm full-width-at-half-maximum) of the microPET scanner. Various nuclei in thalamus and brainstem could be identified. On studies of cerebral glucose metabolism, our findings confirmed the very early functional maturation of sensorimotor cortex, thalamus, brainstem, cerebellar vermis, and limbic structures such as amygdala even in premies. The high ¹¹C-flumazenil binding in basal ganglia, thalamus and brainstem of premature infants was dramatically different from that seen in older children, and may indicate a transient overexpression of GABA[sub]A[/sub] receptors in these structures during development. Whereas glucose metabolism PET scans performed in the ictal state in older subjects typically show hypermetabolism in cortex with propagation patterns involving thalamus, basal ganglia and contralateral cerebellum, ictal PET scans in neonates showed hypermetabolism restricted to cerebral cortex. Heterotopic malformations were clearly identified as areas of increased glucose metabolism with nodular or band appearance in the lower cortical layers or in white matter. In contrast, interictal hypometabolism was of less localization value in newborns because of the normally very low glucose metabolism in most of the cerebral cortex at this age. The Focus 220 microPET scanner is a powerful new approach in the study of neonatal seizures and contributes to the diagnostic evaluation. Metabolic aspects of brain maturation, as well as immaturity in connectivity in newborns, may account for differences in ictal patterns between neonates and older infants.