Age dependency of resistance to cerebrospinal fluid outflow

Resistance to cerebrospinal fluid (CSF) outflow (Rout)is an important parameter in assessing the need for CSF shunt placement in patients with hydrocephalus. The normal lower limit of Rout has been estimated on the basis of the clinical effect of shunt placement in patients with varying values of Rout and in young healthy volunteers. The lack of clinical effect from CSF shunts in some elderly patients, despite elevated Rout,suggests that the normal value of Rout increases with age and may be higher in elderly persons. The aim of the present study was to examine the relationship between Rout and age in patients without known CSF dynamic disturbances.

Fifty-two patients ranging from 20 to 88 years of age and with no known CSF dynamic disorders were examined. The Rout was measured using a lumbar computerized infusion test. The correlation between Rout and age was analyzed by performing linear regression. The Rout increased significantly with patient age. The Rout in a patient in the eighth decade will be approximately 5 mm Hg/ml/minute higher than in a young patient.

The present study shows a small but critical increase in Rout with increased patient age. A notable residual variation was present and borderline values of Rout should be regarded and used with caution.