Objective: Posterior fossa hemorrhages may be underdiagnosed in surviving neonates, with cerebellar hemorrhage discovered in 10% to 25% of autopsy specimens from very low birth weight infants. Posterior fossa lesions have been difficult to visualize by the traditional ultrasonography approach through the anterior fontanelle. Late in 1994, routine posterior fossa imaging through the posterolateral fontanelle was instituted to improve the ultrasonographic visualization of the posterior fossa in neonates.
Methods: Infants identified with posterior fossa hemorrhage by cranial ultrasonography between 1994 and 1996 were followed prospectively through discharge and their clinical courses reviewed. Infants diagnosed with posterior fossa hemorrhage between 1991 and 1994 were identified retrospectively from a comprehensive radiology database to use in comparison. All infants surviving to discharge were entered into neurodevelopmental follow-up using standard developmental assessments.
Results: Approximately 525 infants underwent cranial sonography during the study period between October 1994 and September 1996, including 250 infants weighing <1500 g. Thirteen infants were identified with posterior fossa hemorrhage using the posterolateral fontanellar approach. In contrast, only 2 infants were identified with posterior fossa hemorrhage between 1991 and 1994 using traditional anterior fontanellar views. Six very low birth weight infants were identified with cerebellar hemorrhages not associated with supratentorial, intraventricular hemorrhage. Each hemorrhage had a clinically silent presentation and, in 5 infants, was not well-appreciated by anterior fontanellar images. Magnetic resonance imaging studies were performed on 5 of the 6 infants and confirmed a cerebellar lesion in the area of previous echo density on ultrasonography. No infant is exhibiting motor abnormalities on neurologic examination, although 4 infants are demonstrating cognitive, developmental delay. Follow-up, however, is limited to a corrected age of </=48 months.
Discussion: Cerebellar hemorrhage is an underrecognized and poorly visualized complication in preterm infants. Consistent imaging via the posterolateral fontanelle may demonstrate cerebellar hemorrhage missed by the anterior fontanellar approach. Cerebellar hemorrhage in low birth weight infants may be clinically silent and not associated with a significant supratentorial hemorrhage. These infants may survive to discharge. Long-term neurodevelopmental follow-up is necessary to establish the ultimate outcome of these infants. Future prospective study, using posterolateral fontanellar imaging, may elucidate further the pathophysiology of cerebellar hemorrhage in low birth weight infants.