CSF Flow Dynamics at the Craniovertebral Junction Studied with an Idealized Model of the Subarachnoid Space and Computational Flow Analysis

Sagittal plane views of the craniocervical region in our idealized geometric model, (A) and in a T2-weighted sagittal MR image (VIPR) (B). The craniocervical junction is indicated by a white line, whereas anterior and posterior are indicated by A and P, respectively. The high signal intensity CSF seen in the MR imaging corresponds to the blue-colored region in the model.

Axial MR imaging sections at (A) the craniovertebral junction and (B) at 2 cm below. They show the CSF as high signal intensity and the spinal cord, vertebral arteries, and tissues outside the spinal canal as low signal intensity. Anterior and posterior are indicated by A and P, respectively.

Simulated sagittal plane flow velocities at the time when peak velocity occurred in (A) the cranial direction and (B) the caudad direction. Corresponding parasagittal sections, lateral to the spinal cord, are shown in (C) and (D), respectively. Anterior and posterior are indicated by A and P, respectively. Note that velocities are in the range of 1 to 2 cm/s near the craniovertebral junction and 8 cm/s lower in the spinal canal. (Note also that each color represents an interval of velocities, as specified in the scale to the right in the figure.)

Simulated cephalad-caudal flow velocities in axial sections at the craniovertebral junction (A) and at 6 cm below (B) at the time in the cycle of maximal cephalad (left) and of maximal caudal flow (right). The orientation of each section is as in Fig 3, that is, with the anterior (‘A’) side being upwards, the posterior (‘P’) side being downwards, and the caudal direction being into the page. Note the difference in scale for the 2 section levels. (Note that each color represents an interval of velocities, as specified in the scales to the right in the figure.)

Frontal view of the geometry taken from the 3D animation¹⁴ of flow velocity near the time of peak caudad flow. In the animation, the flow velocities during 1 cycle (repeated) are shown simultaneously in 2 different ways. The leftmost view has “particles” included in the flow, whereas the rightmost has no particles. In the rightmost view, velocities lower than 2 cm/s are not shown. For both views, flow velocities are shown on a color scale from −6 cm/s to 6 cm/s. To simplify the view, velocities outside this chosen range are just shown as maximal scale values. Flow is seen predominantly in a caudad or a cephalad direction, depending on the cardiac cycle. The time at which flow reverses differs in different parts of the subarachnoid space.

Axial images showing bidirectional flow at the craniovertebral junction as flow direction turns from (A) caudal to cranial (ie, from negative to positive at t = 0.5 s) and from (B) cranial to caudal (ie, from positive to negative at t = 1.0 s). (Note that each color represents an interval of velocities, as specified in the scales to the right in the figure.)

Simulated pressures in axial sections at the times when flow direction changed from caudal to cranial (t = 0.5 s) and when flow direction changed from cranial to caudal (t = 1.0 s).

Pressure changes during the second cycle in axial sections 7, 11, 15, and 19 at 4 cm apart and progressively lower in the spinal canal. Section 7 is approximately 1 cm above the craniovertebral junction. The cyclic pressure changes are minimal near the craniovertebral junction (section 7) and are progressively greater with distance along the spinal canal (sections 11–19).