Age dependency of resistance to cerebrospinal fluid outflow

Object. Resistance to cerebrospinal fluid (CSF) outflow (R-out) is an important parameter in assessing the need for CSF shunt placement in patients with hydrocephalus. The normal lower limit of R-out has been estimated on the basis of the clinical effect of shunt placement in patients with varying values of R-out and in young healthy volunteers. The lack of clinical effect from CSF shunts in some elderly patients, despite elevated R-out, suggests that the normal value of R-out increases with age and may be higher in elderly persons. The aim of the present study was to examine the relationship between R-out and age in patients without known CSF dynamic disturbances. Methods. Fifty-two patients ranging from 20 to 88 years of age and with no known CSF dynamic disorders were examined. The R-out was measured using a lumbar computerized infusion test. The correlation between R-out and age was analyzed by performing linear regression. The R-out increased significantly with patient age. The R-out in a patient in the eighth decade will be approximately 5 mm Hg/ml/minute higher than in a young patient. Conclusions. The present study shows a small but critical increase in R-out with increased patient age. A notable residual variation was present and borderline values of R-out should be regarded and used with caution.