Cerebrospinal fluid hydrodynamics after placement of a shunt with an antisiphon device: a long-term study

Object. Few studies have been performed to investigate the cerebrospinal fl uid (CSF) hydrodynamic profile in patients with idiopathic adult hydrocepha lus syndrome (IAHS) before and after shunt implantation. The authors compar ed the in vivo CSF hydrodynamic properties, including the degree of gravity -induced CSF flow, of a shunt with an antisiphon device with a standard shu nt. Methods. Twelve patients with IAHS underwent insertion of shunts with Delta valves. Clinical testing, magnetic resonance imaging, and CSF hydrodynamic investigations were conducted with intracranial pressure (ICP), gravity ef fect, and pressure-flow curve of the shunt estimated at baseline and at 3 a nd 12 months postoperatively. No shunt was revised. Despite postoperative clinical improvement in all patients who received Del ta valves, the mean ICP was only moderately reduced (mean decrease at 3 mon ths 0.3 kPa [p = 0.02], at 12 months 0.2 kPa [not significant]). Patients w ith the greatest increase in ICP preoperatively had the most pronounced dec rease postoperatively. The hydrostatic effect of the Delta valves was signi ficantly lower than with the Hakim shunts (0.1-0.2 kPa compared with 0.6 kP a). The increased conductance (that is, lowered resistance) was up to 14 ti mes higher with the Delta valves compared with preoperative levels. Conclusions. The function of a CSF shunt may be more complicated than previ ously thought; the subcutaneous pressure acting on the antisiphon device ca n modify the shunt characteristics. A compensatory increase in CSF producti on may counteract the increased outflow through the shunt, the improved CSF outflow conductance may increase the intracranial compliance and thereby d ampen a pathological ICP waveform.