Monte Carlo simulation of cerebrospinal fluid shunt failure and definition of instability among shunt-treated patients with hydrocephalus

Object. The authors undertook the present study to estimate the number of operations that patients with hydrocephalus will require within 10 years of diagnosis based on published survival data for cerebrospinal fluid (CSF) shunts. Methods. Survival data for CSF shunts from several previously published sources were formatted as life tables spanning a 10-year period in monthly intervals. The monthly sequence of fractions of shunts failing was taken as the basis for a Monte Carlo simulation. Month by month for each virtual patient the computer simulation called up a random number between 0 and 1. If the random number was greater than the fraction of shunts failing in that monthly interval, the shunt survived. If the random number was less than or equal to the fraction of shunts failing in that interval, the shunt failed. When a virtual patient's shunt failed, that patient was returned to the first interval in the life table and began again. For every virtual patient this process continued for 120 months, and the number of shunt operations during the 10-year epoch was counted. Probability distributions were estimated for numbers of shunt operations. Expected numbers of shunt operations were calculated, as were the 95th and 99th percentiles. Results. Four sources of CSF shunt survival data were used. Expected numbers of shunt operations ranged between 2.43 and 3.93 over 10 years. Estimated 95th percentiles ranged between five and 11, and estimated 99th percentiles ranged between eight and 15. Conclusions. New patients with hydrocephalus can expect to undergo between two and four operations for insertion or revision of CSF shunts in the first 10 years after diagnosis. Patients who undergo more than 15 shunt operations in 10 years are statistical outliers. A focused study of such patients may yield useful suggestions for complication avoidance and improvement in the quality of life of children with hydrocephalus.