Slight elevation of baseline intracranial pressure after fluid infusion into CSF space in patients with hydrocephalus

OBJECTIVE: To investigate the elevation of resting cerebrospinal fluid (CSF) pressure recorded after a CSF infusion test in patients with hydrocephalus. MATERIAL AND METHODS: Fifty patients (30 men and 20 women, mean age 68 +/- 13 years) with ventriculomegaly and clinical symptoms of normal pressure hydrocephalus have been studied. Lumbar (56%) or intraventricular (44%) computerized infusion studies were performed to investigate the hydrodynamics of CSF. After infusion, the fall in ICP was recorded until a steady-state level was achieved and the difference between pre- and post-infusion resting ICP was calculated (DeltaICP). RESULTS: A positive difference (>2 mm Hg) between post- and pre-infusion resting ICP was identified in 31 infusion tests (62%). The mean value of the difference was 6.7 with an SD of 3.5 mm Hg. The patients who demonstrated this phenomenon had a greater elastance coefficient (p>0.05); DeltaICP was positively correlated with age (R=0.27; p=0.03), with the size of the brain's ventricles (R=0.63, p=0.03) and inversely with the severity of clinical impairment (Stein-Langfitt score R=-0.61, p=0.02; normal pressure hydrocephalus score: R=0.54; p<0.05). DeltaICP was independent of the site of infusion (lumbar or ventricular). CONCLUSION: In patients with a 'stiffer' brain, ICP returns to the resting level after the infusion test at a slightly higher level than before the test. The magnitude of this increase is greater when ventricles are more dilated and clinical symptoms are less severe.