Objective: To determine ICP changes in patients with Chiari type I malformation after posterior fossa reconstruction (PFR).
Patients and methods: We continuously monitored ICP before and after PFR in 12 patients with Chiari I malformation and with an Evans' Index below or equal to 0.33. Mean ICP (epidural sensor) and percentage of B waves were calculated 24 hours before surgery and during the first 7 days after surgery.
Results: Mean ICP and percentage of B waves significantly increased after surgery despite a significant increase in the volume of the posterior fossa. The main finding revealed by control CT scans was compression of the quadrigeminal cistern with a reduction in size of the fourth ventricle. In six patients, a small transitory increase in supratentorial ventricular size was found.
Conclusions: A transitory increase in ICP is common after PFR. This increase could be explained by an initial reperfusion phenomena in the cerebellum that provokes a transitory deterioration in CSF dynamics. The effacement of the quadrigeminal cistern and the reduction in size of the fourth ventricle suggests this hypothesis.