Posture-induced changes in intracranial pressure: a comparative study in patients with and without a cerebrospinal fluid block at the craniovertebral junction.

OBJECTIVE: The aim of this study was to determine posture-induced changes in intracranial pressure (ICP) when patients with hydrocephalus or idiopathic intracranial hypertension remained supine for 1 hour and then sat up and remained sitting for 3 hours.

METHODS: Continuous ICP was monitored using a fiberoptic extradural sensor in: 1) 259 patients with hydrocephalus or idiopathic intracranial hypertension with free cerebrospinal fluid (CSF) flow through the craniovertebral junction and Sylvian aqueduct, 2) 20 patients with hydrocephalus secondary to aqueductal stenosis with free CSF flow through the craniovertebral junction, and 3) 97 patients with hydrocephalus associated with Chiari malformation. The maximum ICP difference (DeltaICP) was calculated as the difference between mean ICP in the supine position and minimum ICP value after changing body position. The mean ICP difference (DeltaICPmean) was calculated as the difference between the mean ICP in the supine position and the mean ICP while the patient was in a sitting position.

RESULTS: In the complete sample, the median of DeltaICP was 13 mm Hg (interquartile range 10-17). The median of DeltaICPmean was 8 mm Hg (interquartile range 5-11). Both DeltaICP and DeltaICPmean were significantly greater in patients without obstruction in the craniospinal junction than in those with Chiari malformation (P = 0.005 and P = 0.014, respectively). No differences were found in DeltaICP or DeltaICPmean between patients with Sylvian aqueduct stenosis and those without (P = 0.777 and P = 0.346, respectively).

CONCLUSION: ICP reduction after a change in body position is significantly greater in patients with free CSF flow through the craniospinal junction than in those with Chiari malformation, indicating the difficulty or impossibility of CSF displacement into the spinal canal in the latter.