Physiology-based MR imaging assessment of CSF flow at the foramen magnum with a valsalva maneuver

Abstract

Background and purpose: MR imaging is currently not used to evaluate CSF flow changes due to short-lasting physiological maneuvers. The purpose of this study was to evaluate the ability of MR imaging to assess the CSF flow response to a Valsalva maneuver in healthy participants.

Materials and methods: A cardiac-gated fast cine-PC sequence with ≤15-second acquisition time was used to assess CSF flow in 8 healthy participants at the foramen magnum at rest, during, and immediately after a controlled Valsalva maneuver. CSF mean displacement volume VCSF during the cardiac cycle and CSF flow waveform App were determined. A work-in-progress real-time pencil-beam imaging method with temporal resolution ≤56 ms was used to scan 2 participants for 90 seconds during which resting, Valsalva, and post-Valsalva CSF flow, respiration, and HR were continuously recorded. Results were qualitatively compared with invasive craniospinal differential pressure measurements from the literature.

Results: Both methods showed 1) a decrease from baseline in VCSF and App during Valsalva and 2) an increase in VCSF and App immediately after Valsalva compared with values measured both at rest and during Valsalva. Whereas fast cine-PC produced a single CSF flow waveform that is an average over many cardiac cycles, pencil-beam imaging depicted waveforms for each heartbeat and was able to capture many dynamic features of CSF flow, including transients synchronized with the Valsalva maneuver.

Conclusions: Both fast cine-PC and pencil-beam imaging demonstrated expected changes in CSF flow with Valsalva maneuver in healthy participants. The real-time capability of pencil-beam imaging may be necessary to detect Valsalva-related transient CSF flow obstruction in patients with pathologic conditions such as Chiari I malformation.

Fig 1.

Schematic of Valsalva device used for experiments. Participants were directed to exhale into the plastic tubing with sufficient force to hold the end of the bellows at the 40-cm H₂O mark on the clear plastic cylinder. This provided a consistent and reproducible Valsalva-generated pressure.

Fig 2.

Sagittal and coronal T2-weighted images show PBI excitation cylinder extending from above the level of the foramen magnum to the C2–3 disk level.

Fig 3.

Cardiac cycle–dependent CSF flow before, during, and after a Valsalva maneuver in 1 participant by using fast cine-PC imaging. Flow in milliliters per second is shown as a function of time, normalized to the cardiac cycle. During Valsalva, V̄_CSF and A_pp decreased compared with resting. After Valsalva, both V̄_CSF and A_pp increased compared with during the maneuver, rebounding to values larger than resting.

Fig 4.

Figure shows invasive pressure measurements vs time. Trace 4 shows heartbeat-by-heartbeat changes in lumbar minus ventricular pressure (craniospinal pressure differential) with Valsalva. Note the similarities between trace 4 and CSF flow waveforms (panel 2) in the On-line figure. Note further that PBI captured many dynamic CSF flow features including transients precisely synchronized with timing of Valsalva similar to that seen here. Reproduced from Williams B. Simultaneous cerebral and spinal fluid pressure recordings. I. Technique, physiology, and normal results. Acta Neurochir (Wein) 1981;58:167–85 with kind permission from Springer Science and Business Media.