Objective: To evaluate factors involving acute hydrocephalus in posterior fossa injuries, and assess managements for these hydrocephalus. Methods: Retrospective study of 41 patients with acute hydrocephalus in posterior fossa injuries treated at Viet-Duc hospital from 1/2008 to 7/2011. Results: female/male: 1/7, mean age 32,6. Main lesions of posterior fossa: 26.8 percent extradural hematomas
intracerebellar hematomas and contusions 41.5 percent
subdural hematomas 19.5 percent
associated supratentorial lesions 70.7 percent
bilateral hematomas 63.4 percent. Thickness of hematoma 3cm 78 percent
all patients show citernal anormalities
effaced 4th ventricule in 58.5 percent. Conclusion: The risk factors of acute hydrocephalus consist of intracerebellar hematomas and contusions, thickness of hematoma 3cm, not visualized cisterns, and 4th ventricule effaced. External ventricular drainage depends on lesion. In case of extradural hematomas, derivation is unnecessary. Otherwise, drainage is really effective.