Beneficial effect of siphoning in treatment of adult hydrocephalus

Objective: To increase awareness about the treatment of adult patients with shunt-nonresponsive hydrocephalus-a state characterized by marked ventricu lomegaly, low intracranial pressure, and a patent cerebrospinal fluid diver sionary shunt. Design: Retrospective analysis of hospital and outpatient records. Patients: Four patients with symptomatic ventriculomegaly and patent ventri culoperitoneal shunts treated with a protocol of progressive ventricular hy potension induced by external cerebrospinal fluid drainage. Results: Severe clinical manifestations exhibited by the patients, includin g parkinsonian features, Parinaud syndrome, and extensor posturing, complet ely reversed once a normalization of ventricular size was achieved. Externa l ventricular drainage pressures as low as -30 cm H2O were required to redu ce ventricular size. All patients finally received a shunt incorporating a standard medium differential pressure valve with no antisiphon device. Conclusions: Shunt siphoning may be an essential mechanism by which cerebro spinal fluid shunting is effective in many patients with adult hydrocephalu s. Cerebrospinal fluid shunts that contain an antisiphon device are ineffec tive in these patients, despite the attainment of "physiologic" intracrania l pressures. Based on reported experimental and clinical evidence, it seems that the cause of this condition may be related to abnormally high intracr anial compliance.