Change in ventricular size and effect of ventricular catheter placement inpediatric patients with shunted hydrocephalus

OBJECTIVE: The multicenter, randomized pediatric cerebrospinal fluid shunt valve design trial found no difference in the rate of shunt failure between a standard valve, a siphon-reducing valve (Delta; Medtronic PS Medical, Go leta, CA), and a flow-limiting valve (Orbis Sigma; Cordis, Miami, FL); howe ver, the valves were expected to have different effects on ultimate ventric ular size. Also, the catheter position or local environment of the ventricu lar catheter tip might have affected shunt failure. Therefore, we performed a post hoc analysis to understand what factors, other than valve design, a ffected shunt failure and to identify strategies that might be developed to reduce shunt failure. METHODS: Ventricular size was measured at as many as six different interval s, using a modified Evans' ratio (with incorporation of the frontal and occ ipital dimensions), in 344 patients. Ventricular catheter location was defi ned as being in the frontal horn, occipital horn, body of the lateral ventr icle, third ventricle, embedded in brain, or unknown. The ventricular cathe ter tip was described as surrounded by cerebrospinal fluid, touching brain, or surrounded by brain parenchyma within the ventricle (slit ventricle). R epeated measures analysis of variance for unbalanced data was used to analy ze ventricular size. A Cox model (with incorporation of time-dependent cova riates) was used to evaluate the contribution of age, etiology, shunt desig n, ventricular size, ventricular catheter location, and environment among t he cases. RESULTS: Ventricular volume decreased in an exponential fashion, forming a plateau at 14 months, and was similar for the three valves (P = 0.4). Front al and occipital ventricular catheter tip locations were associated with a reduced risk of shunt failure (hazard ratios, 0.60 [P = 0.02] and 0.45 [P = 0.001], respectively). Ventricular catheter tips surrounded by cerebrospin al fluid or touching the brain were associated with a reduced risk of failu re (hazard ratios, 0.21 and 0.33, respectively; P = 0.0001). Patients with myelomeningocele or large ventricles had increased risk of malfunction (haz ard ratios, 1.78 [P = 0.006] and 2.33 [P = 0.03], respectively). CONCLUSION: Decline of ventricular size over time is not affected by these different shunt valve designs. This suggests that the mechanical models of hydrocephalus on which the designs were based are inadequate. Ventricular c atheter tip location and ventricular catheter environment are important. Te chniques to accurately place ventricular catheters and new valve designs th at effectively control ventricular size might reduce shunt malfunction.