Timing of brain insults in severe neonatal encephalopathies with isoelectric EEG.

In a neonatal intensive care unit of a large obstetric hospital, 20 neonates (7 preterm, 9 term, 4 postterm) with at least one isoelectric recording were treated over a 6-year period. Seventy-four EEGs were obtained in this cohort, including 36 isoelectric recordings. Seven infants in this group had evidence of a predominant antepartum component of a pathologic process based on placental, postmortem examination findings, or clinical history. Of the 16 placentas available for review, chronic lesions were observed in 13 of 16 specimens, including villitis, infarction, dysmaturity, and thrombosis. Seven of 9 patients with postmortem neuropathologic examinations had evidence of chronic lesions, principally neuronal necrosis, infarction, and microcalcifications. An additional 10 infants had evidence of an antepartum contribution to a pathologic process that continued into either the intrapartum or neonatal periods, based on maternal and/or neonatal medical factors. Clinical findings supportive of antepartum insults included intrauterine growth retardation, antepartum hemorrhage, abnormal antepartum fetal heart rate patterns, and maternal medical complications. Three patients had either intrapartum- or neonatal-onset of injury. Clinical signs of severe encephalopathy, however, were present in the immediate postnatal period in most patients (18 of 20; 90%). Assessment of clinical and pathologic information on neonates with isoelectric EEGs may estimate the timing of brain injury to the antepartum period, as opposed to, or in addition to, the labor and delivery periods. A neonate who suffered brain injury before parturition may be neurologically depressed after birth with absence of electrocerebral activity on EEG.