Cerebrospinal Fluid Flow Void Sign

The cerebrospinal fluid (CSF) flow void sign (CFVS), also known as the aqueductal flow void sign, classically referred to hypointensity in the Sylvian aqueduct as a result of to-and-fro CSF flow. The to-and-fro flow is due to pulsatile motion of CSF related to the cardiac cycle. It can also be observed in the fourth ventricle (~95% of cases), the third ventricle (70% of cases), foramen of Magendie (~75% of cases), and the foramina of Monro (~30% of cases).

On T1-weighted images, CSF signal is replaced by signal that is lower than that of the contents of the lateral ventricles. On T2-weighted images, there is low signal instead of the expected hight fluid signal.

The CFVS can be seen in normal individuals, and in those with brain atrophy, but is more pronounced in patients with chronic, communicating normal pressure hydrocephalus (NPH). Unfortunately, the sign does not appear to be useful in differentiating patients with NPH from those with brain atrophy.

The presence of CFVS, along with more extensive periventricular hyperintensities, are felt to have positive prognostic value in patients who are treated for NPH.

References

• Bradley WG Jr, Kortman KE, Burgoyne B. Flowing cerebrospinal fluid in normal and hydrocephalic states: appearance on MR images. Radiology. 1986 Jun;159(3):611-6.
• Sherman JL, Citrin CM, Gangarosa RE, Bowen BJ. The MR appearance of CSF flow in patients with ventriculomegaly. AJR Am J Roentgenol. 1987 Jan;148(1):193-9.