Magnetic resonance imaging in the evaluation of cerebrospinal fluid flow abnormalities.

Phase contrast magnetic resonance imaging techniques can be used to evaluate the to-and-fro motion of cerebrospinal fluid (CSF) throughout the ventricles and subarachnoid space of the brain and spine. This CSF motion is due to transmitted cardiac pulsations from systolic expansion of the cerebral hemispheres. To cover the entire cardiac cycle, retrospective cardiac gating (rather than electrocardiographic triggering) must be used. Using this technique, it is possible to quantify CSF motion over a cardiac cycle and to distinguish normal aqueductal CSF "stroke volumes" from those seen in atrophy and shunt-responsive communicating hydrocephalus. Arachnoid cysts and other loculated CSF collections can be diagnosed using a "rebound sign" in which the motion of the CSF within the cyst is 90 degrees phase advanced over the CSF flowing around it.