Observation of the CSF pulsatile flow on MRI, (1)

In a retrospective study of the MRI images of 289 neurosurgical patients, a loss of the signal intensity (the signal void phenomenon, SVP for short) of the cerebrospinal fluid in the mesencephalic aqueduct was observed in 77 patients. The SVP, which should generally be found at a flow velocity above 6 to 10 cm/sec, cannot be caused by CSF production alone, for it is inadequate to cause a flow rate of this magnitude, even in the narrowest part of the aqueduct. For CSF to flow at the rate of several centimeters per second or more, it is necessary for brain pulsation to synchronize with the cardiac systole and diastole to make the CSF move to-and-fro between the cranium and the spinal cavity. Another eight patients were studied with ECG-triggered MRI. The change in the CSF signal intensity against the time-related brain pulsations transmitted from cardiac systole and diastole shows that the CSF signal intensity changes by the delay time after the R wave. This result indicated that the CSF flow had a to-and-fro movement during the R-R interval. Therefore, it was speculated that the CSF flow could be fast enough to cause the SVP in a small channel or foramen, such as the aqueduct of Sylvius or the foramen of Monro. These considerations permit us to confirm that the change in the CSF signal intensity revealed on ECG-triggered MRI indicates the variation in the CSF flow, visualizing the CSF pulsatile flow. (author)