The authors describe an infant with abnormal development of the cerebral venous system associated with in utero ventriculomegaly and perinatal hemorrhage. When the patient was 6 weeks of age progressive ventriculomegaly followed by cerebrospinal fluid diversion resulted in tumefaction of the dural sinuses, intravascular thrombosis, and a coagulopathy. Oral anticoagulation therapy safely reversed the coagulopathy. Serial neuroimaging findings in this unique cascade of pathophysiological events indicated that, despite decreased intracranial pressure after shunt placement, local hemodynamic factors increased the venous resistance to flow and prolonged the transit time. Long-term anticoagulation therapy was associated with improvements in flow, transit time, and tumefaction.