Symptomatic progressive ventriculomegaly in hydrocephalics with patent shunts and antisiphon devices.

The antisiphon device (ASD) was designed to prevent excessive negative intracranial pressure and overdrainage with cerebrospinal fluid shunts. It has been recommended for prevention of slit ventricles and extreme shunt dependency. It was used by the author in 40 children and young adults who had low pressure headaches or were judged to be at risk for the development of subdural hematomas because of extreme hydrocephalus, relatively fixed head size, or tall stature. Nine patients encountered problems with adverse symptoms in spite of shunt patency. Four had alarming neurological symptoms of coma or severe headaches after incorporation of ASDs in ventriculoperitoneal shunt systems. With patients in the horizontal position, shunt patency was documented but computed tomography revealed progressive ventriculomegaly when they were kept erect. Symptoms abated and ventricular size diminished after conversion to proximal medium pressure diaphragm or spring-ball valve systems without ASDs. Because long shunt systems with ASDs require adequate hydrostatic columns to initiate flow when patients are erect, it is theorized that such symptoms could have been prevented by placing ASDs farther downstream from the cerebral ventricles.