Etiological differences between the isolated lateral ventricle and the isolated fourth ventricle

Objective To determine if an etiological difference exists between isolation of the lateral ventricle and isolation of the fourth ventricle after ventricular shunting.Methods Cases of symptomatic isolation of the lateral and fourth ventricles were reviewed retrospectively. The ages at presentation of ventricular isolation, the time course to development of isolation, the number of shunt surgeries leading up to symptomatic isolation, the types of shunt valves utilized, and the background of infection were analyzed.Results Twenty-six patients had lateral ventricle isolation and 11 patients had fourth ventricle isolation. Infection, hemorrhage, Chiari malformation/myelomeningocele, and aqueductal stenosis were factors contributing to hydrocephalus requiring treatment in these patients. Compared to 26.9% of patients with lateral ventricle isolation, 90.9% of patients with fourth ventricle isolation had a previous history of infection.Conclusions Prior meningitis and ventriculitis frequently contributed to fourth ventricle isolation. Lateral ventricle isolation seems to arise from functional obstruction of the foramen of Monro related to prior shunting.