Peak systolic and diastolic CSF velocity in the foramen magnum in adult patients with Chiari I malformations and in normal control participants

Abstract

Background and purpose: Abnormal flow of CSF through the foramen magnum has been implicated in the pathogenesis of clinical deficits in association with Chiari I malformation. The purpose of this study was to test the hypothesis that peak CSF velocities in the foramen magnum are increased in patients with Chiari I malformations.

Methods: Eight adult patients with symptomatic Chiari I malformations and 10 adult volunteers were studied with cardiac gated, phase-contrast MR imaging in the axial plane at the foramen magnum. The spatial uniformity of flow velocity in the foramen magnum was assessed at 14 time frames within the R-R interval. The velocity in each of the voxels at each of the time frames was calculated, and the peak systolic and diastolic velocities were tabulated for the patients and controls.

Results: For the normal volunteers, the CSF velocities in the subarachnoid space were relatively uniform throughout the subarachnoid space at each of the time frames. Peak systolic velocity ranged from 1.2 to 3.3 cm/s, and peak diastolic velocity ranged from 1.6 to 4.5 cm/s. In symptomatic patients with Chiari I, velocities in the foramen magnum did not appear as uniform throughout the subarachnoid space in the phase-contrast images. Peak systolic velocities ranged from 1.8 to 4.8 cm/s, and peak diastolic velocities ranged from 2.5 to 5.3 cm/s. Peak systolic velocity was significantly higher (P =.01) in the patients than in the control volunteers.

Conclusion: Patients with Chiari I malformations have significant elevations of peak systolic velocity in the CSF in the foramen magnum.

Fig 1.

Phase contrast images of the foramen magnum in a normal volunteer. The images are displayed in vbgor color scale, with violet and blue showing flow in the caudad (negative) direction and orange and red showing flow in the craniad (positive) direction. The scale is set to +3 to −3 cm/s. The 14 consecutive images through the cardiac cycle from top left to lower right (A) show fairly uniform flow velocities within the foramen magnum. In one image from the series (B), the subarachnoid space is highlighted by means of an oval placed by an illustrator and the vertebral arteries are designated by arrows.

Fig 2.

Phase-contrast image and flow measurements of a normal volunteer. Selected region of interest (left), labeled F1, is illustrated on one of the flow images. Maximum flow velocity in the region of interest for the 14 time points is illustrated graphically (right). Maximum systolic (between trigger delays of 250 and 1021 ms) and diastolic (first 250 and last 100 ms) velocities are approximately 2 cm/s. Velocities are relatively uniform throughout the subarachnoid space.

Fig 3.

Image of the foramen magnum in a normal volunteer shows the placement of three regions of interest (left) and maximal velocities displayed graphically over time (right) for each of the regions of interest. One of the regions of interest encompasses the entire subarachnoid space, and two smaller regions of interest sample portions of the subarachnoid space. Flow in each region of interest has similar temporal patterns and magnitudes. Systolic flow is evident from trigger delays of approximately 160 ms to approximately 860 ms in each of the regions of interest.

Fig 4.

Representative phase contrast images of the foramen magnum in a patient (A) with the same vbgor color scale as in the normal subject. Flow velocities differ markedly in different regions in the subarachnoid space. Velocities anterior to the cord exceed those posterior to the cord. Velocities in the anterolateral subarachnoid space, exceed those elsewhere in the subarachnoid space, especially in diastole. A single frame (B) from late diastole is shown with a cursor placed to illustrate the region in which flow was measured (white oval) and the vertebral arteries (arrows). Note that flow in the subarachnoid space reverses while flow in the vertebral artery has continuous flow.

Fig 5.

Phase contrast images throughout the cardiac cycle in a patient (A) show inhomogeneous flow. These show inhomogeneity of flow, greater velocities anterior to the cord than posterior, greater velocities paramidline than in the midline and greater velocities in the craniad direction than in the caudad direction. An oval is placed on one image with a long trigger delay obtained during diastolic flow of CSF. An enlargement of that image (B) shows a region of aliasing (arrow) within the subarachnoid space in which flow velocity exceeded the venc.

Fig 6.

Phase-contrast image (left) of the foramen magnum shows the placement of a region of interest. Graph of the maximal velocities (right) throughout the cardiac cycle in the selected region of interest in a patient with a Chiari I malformation and a syrinx. Peak velocities during systole and diastole are 4.8 cm/s.

Fig 7.

Phase-contrast image (left) and graph of velocities (right) show velocity aliasing during caudad flow of CSF in the foramen magnum of a patient. In the image a region of bright white signal intensity anterior and to the right of midline is surrounded by dark black signal intensity. The graph indicates that flow for the region of interest appears to turn negative (dark) at 30-ms trigger delay and then unexpectedly reverts to positive from approximately 60-ms trigger delay to approximately 260-ms trigger delay. The apparent reversal of sign in the graph and in the image result from velocity aliasing.

Fig 8.

Illustration of aliasing of craniad flow in a patient. In a sagittal view image (upper left), the location of the axial plane is indicated by a white line. In an axial view image showing craniad flow at 51-ms trigger delay (lower left), the location of a region of interest is illustrated. An arrow in this image obtained during the first 50 ms of the cardiac cycle indicates a region of inverted sign. In the graph of CSF velocity, flow paradoxically has a negative sign during the first 50 and last 50 ms of the cardiac cycle, indicating aliasing during diastole.