Isolation of the fourth ventricle causing transtentorial herniation: neurosonographic findings in premature infants.

Objective: Significant posthemorrhagic enlargement of the fourth ventricle occurs only in a small minority of patients. Although entrapment or isolation of any ventricle can occur, the fourth ventricle is the most common site. This study was undertaken to better understand enlargement of the fourth ventricle after intraventricular hemorrhage and the neurosonographic features of isolation and transtentorial herniation.

Materials And Methods: The sonographic records of 1535 premature neonates were reviewed for evidence of intracranial hemorrhage and ventriculomegaly. Cranial sonography was performed within the first 3 days of life in all neonates born in our hospital and within the first week of admission for transferred neonates. Follow-up sonograms were obtained at weekly intervals until discharge from the nursery. Intracranial hemorrhages were classified as severe when the hemorrhage was associated with hydrocephalus, intraparenchymal hemorrhage, or both.

Results: Intracranial hemorrhage occurred in 761 (50%) of 1535 patients, with severe hemorrhages in 229. Ten had massive enlargement of the fourth ventricle with isolation in six of the 10 after shunt placement. Isolation of the fourth ventricle causing transtentorial herniation occurred in three. Of the patients with isolation of the fourth ventricle, two had associated infection and ventriculitis caused by Klebsiella oxytoca and one had Candida ventriculoencephalitis.

Conclusion: The early recognition of the neurosonographic features of an enlarged fourth ventricle causing transtentorial herniation has important therapeutic implications. Although isolation can occur after intraventricular hemorrhage alone, infection and ventriculitis are significant factors in the development of an isolated fourth ventricle.