Amplitude and phase of cerebrospinal fluid pulsations: experimental studies and review of the literature

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A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow.


Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging.

The stroke volume ratio was 5.1 ± 1.8% (mean ± standard deviation). The phase lag in the aqueduct was −52.5 ± 16.5° and the phase lag in the prepontine cistern was −22.1 ± 8.2°. The flow phase at the level of C-2 was +5.1 ± 10.5°, which was consistent with flow synchronous with the arterial pulse. The subarachnoid phase lag ventral to the pons was shown to decrease progressively to zero at the craniocervical junction. Flow in the posterior cervical SAS preceded the anterior space flow.


Under normal conditions, pulsatile ventricular CSF flow is a small fraction of the net pulsatile CSF flow in the cranium. A thorough review of the literature supports the view that modified intracranial compliance can lead to redistribution of pulsations and increased intraventricular pulsations. The phase of CSF flow may also reflect the local and global compliance of the brain.

Abbreviations used in this paper:BA = basilar artery; CA = carotid artery; CSF = cerebrospinal fluid; FOV = field of view; MR = magnetic resonance; NPH = normal-pressure hydrocephalus; SAS = subarachnoid space; SNR = signal-to-noise ratio; SD = standard deviation; SSS = superior sagittal sinus; Venc = encoding velocity.

Article Information

Address reprint requests to: Mark E. Wagshul, Ph.D., Department of Radiology, HSC L4–109, Stony Brook University, Stony Brook, New York 11794–8460. email:

© AANS, except where prohibited by US copyright law.



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    Typical oblique axial velocity image obtained early in the cardiac cycle, demonstrating caudal CSF flow through the aqueduct (arrow).

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    Upper: Graph showing aqueductal CSF flow waveform. The data were obtained by summing all flow pixels within the aqueduct. This particular data set shows a peak flow of 179 μl/second and a total stroke volume of 35.2 μl. Lower: Carotid arterial flow. There is excellent agreement between the velocity data (squares) and the two-harmonic model fit (circles).

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    Graphs demonstrating the two primary amplitude measures of CSF flow in all study participants: aqueductal stroke volume (SV; upper) and stroke volume ratio (lower). Stroke volume was calculated as the total amount of CSF pulsating through the cerebral aqueduct in the caudal (or rostral) direction with each heartbeat. Stroke volume ratio was calculated as the ratio of net systolic flow between the aqueduct and the cervical SAS. The average stroke volume for the group was 30.9 μl and the average stroke volume ratio was 5.1%.

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    Plot showing the extracted phase of flow waveforms in the cerebral aqueduct (diamond), in the prepontine (PP) cistern (square), and at the level of C-2 (triangle), calculated relative to the average phase in the CAs, shown for 14 study participants. The data demonstrate an approximate phase of zero in the cervical SAS, whereas the flow phase in more cranial CSF regions lag in time.

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    Mean flow phase values for all study participants relative to the phase in the CAs. The anterior SAS was split into three approximately equal-length regions. Ant = anterior; post = posterior; sag = sagittal.



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