Revision to an adjustable non-siphon control valve in low pressure hydrocephalus: Therapeutic siphoning and a new perspective on NPH: Series of 3 cases and review of the literature

IntroductionHigh intracranial compliance states requiring negative pressure drainage, otherwise known as low-pressure hydrocephalus syndromes, are rare conditions. The use of siphoning, enabled by revision to an adjustable shunt without an anti-siphon device, has been largely unexplored in low-pressure hydrocephalus.MethodsThree patients with presumed normal pressure hydrocephalus (NPH) presented with unresolved symptoms, including urinary incontinence, disturbed gait, and cognitive dysfunction. Each was inadequately treated despite confirmed functioning Strata II valves (with built-in siphon control device) calibrated to the lowest pressure setting for maximum drainage. Surgical revision to Strata non-siphon control (NSC) valves was performed to allow for additional drainage via siphoning.ResultsFollowing revision to a shunt with a “siphoning” device, each patient achieved improved neurological function. Each differential pressure valve was initially set to a higher setting than with the Strata II valve. One of our patients experienced the formation of a subdural hematoma after shunt revision; resolution following adjustment of the valve to a higher setting suggests that siphoning may be of less importance to overdrainage syndromes when compared with valve opening pressure.ConclusionOur findings indicate that intermittent intracranial hypotension achieved by siphoning is effective in the treatment of a subset of patients presenting clinically with NPH. Direct conversion to a shunt system without an anti-siphon device allows reduction of ventricular size without the risk associated with external ventricular drainage (EVD). With conversion to the Strata NSC valve, our patients had sustained clinical improvement, even at higher valve settings.