CEREBROSPINAL-FLUID SHUNT DYNAMICS IN PATIENTS WITH IDIOPATHIC ADULT HYDROCEPHALUS SYNDROME

The objective was to assess CSF dynamics of different shunt constructi ons in patients with adult hydrocephalus syndrome and correlate these findings to clinical outcome, neuroradiology, and the specifications o f the shunts provided by the manufacturer. Thirty four patients with i diopathic adult hydrocephalus (normal pressure hydrocephalus) syndrome were included in a prospective, consecutive case series. A differenti al pressure valve (Cordis Hakim standard system) was used in 28 patien ts and a variable resistance valve (Cordis Orbis-Sigma) in six. A cons tant pressure infusion method was used; CSF pressure and conductance w ere determined before surgery. Three months after shunt placement CSF pressure, the ''pressure v flow'' curve, and gravity induced flow were measured. There was no difference between mean preoperative and posto perative resting CSF pressures in patients with Hakim shunts. The open ing pressures of the Hakim shunts were higher than the value proposed by the manufacturer. A pronounced gravity effect induced CSF flow and decrease of the CSF pressure. In functioning variable resistance valve s, CSF dynamics normalised postoperatively. There was no gravity effec t and the characteristic s shaped ''pressure v flow'' curve was someti mes seen. Six patients (three differential pressure valves, three vari able resistance valves) had non-functioning shunts. Four of these pati ents were improved after the operation but improvement was transient i n three. In all patients, there was no relation between the width of t he ventricles and clinical improvement or CSF pressure. In conclusion, the differential pressure valve system does not behave according to t he specifications provided by the manufacturer. A decrease in CSF pres sure in patients with this shunt was solely due to the effect of gravi ty. Eleven per cent of the differential pressure valves and 50% of the variable resistance valves were non-functioning. In the functioning v ariable resistance valves, the antisiphon system seems to be effective .