Objective: Patients with Idiopathic Normal Pressure Hydrocephalus are improved with shunt surgery. To increase the accuracy of the diagnosis, supplementary tests that characterize the cerebrospinal fluid (CSF) dynamics are used. The infusion test is one of these, used for shunt surgery selection and postoperative evaluation of shunt function. Forty-eight patients that had a preoperative investigation because of communicating hydrocephalus at the university hospitals in Umeå and Uppsala, Sweden, participated in the study. The purpose of this study was to evaluate a new method, with a new infusion protocol and new analysis methods, and compare it to the current method.

Inclusion Criteria:

• preoperative investigation because of communicating hydrocephalus
• ventriculomegaly (Evans ratio > 0.3)
• no obstruction to CSF flow at visual inspection

Exclusion Criteria:

• postoperative infusion test investigations
• patients that were unable to understand instructions

Patients that had a preoperative investigation because of communicating hydrocephalus. MRI revealed ventriculomegaly (Evans ratio > 0.3), no obstruction to CSF flow at visual inspection. Most, but not all, fulfilled the criteria of "probable" or "possible" INPH.