Effect of Tonsillar Herniation on Cyclic CSF Flow Studied with Computational Flow Analysis

Sagittal plane sections showing flow velocities in the Chiari model at the time when the caudal volume flow rate is maximal (t = 0.25 seconds, A) and when cranial volume flow rate is maximal (t = 0.75 seconds, B). C and D, For comparison, corresponding sections in the normal model are shown. Velocity scales in are the same as in A and B, respectively. The plane selected for the Chiari model is paramidline to demonstrate the extension of the tonsils into the spinal canal.

Axial sections show flow velocity at the craniovertebral junction in the Chiari model at the time when caudal volume flow rate is maximal (t = 0.25 seconds). B, For comparison, a corresponding section for the original model (without tonsil herniation) is shown at an equivalent time in the cycle. Note that the distribution of peak velocities in both models is similar and that in the presence of tonsillar herniation, velocities are more than double those in absence of tonsillar herniation.

Axial sections showing the LR (A) and AP components (B) of the flow velocity vector at the craniovertebral junction in the Chiari model at the time when the caudal volume flow rate is maximal (t = 0.25 seconds). C and D, Similar velocity components are also shown, when cranial volume flow rate is maximal (t = 0.75 seconds). Velocity scales are the same as in A and B, respectively.

A single frame from the particle-tracking display for the Chiari model shows a complex pattern of CSF movement in 1 portion of the subarachnoid space. Note the arrows in multiple directions. The animation (http://home.simula.no/∼sveinlin/CSFChiari.m1v) displays CSF movement by means of particle tracking (left) and color coding (right) over 5 cardiac cycles, while the model is rotated 360°. The particle-tracking animation displays the direction of CSF flow; the color animation displays the velocity of flow. For the color display, velocities of ≥6 cm/s in the caudal direction are displayed in blue and ≥6 cm/s in the cephalad direction in red. The displays show complex flow patterns, especially when flow direction reverses. Flow transiently occurs in a direction perpendicular to that of the SI. Flow direction in different locations in the subarachnoid space changes at slightly different times in the cardiac cycle. Peak velocities in both caudal and cephalad directions appear to be reached in the spinal canal before they are reached at the craniovertebral junction. In comparison with the normal model (http://home.simula.no/∼sveinlin/CSFnormal.mpg), greater velocities are found in the craniovertebral junction and greater complexity of flow is demonstrated as flow direction changes.

Peak velocity components (absolute values) for the Chiari model (solid lines) and the normal model (dotted lines). The SI (black), LR (red), and AP (blue) velocity components are shown in 4 axial sections at 4 different times during the flow cycle, when flow changes direction from cranial to caudal (t = 0.00 seconds), at maximal caudal flow (t = 0.25 seconds), when flow changes direction from caudal to cranial (t = 0.50 seconds), and, finally, at maximal cranial flow (t = 0.75 seconds). Sections are 1 cm apart, with section 1 located at the craniovertebral junction, and sections 3–7, at successively more inferior locations, with section 7 being near the tip of the tonsils.

Peak SI flow velocities at the time when the caudal volume flow rate is maximal (t = 0.25 seconds), shown as a function of the axial section for the Chiari model and the normal model. Section 1 is at the craniovertebral junction, and section 8 is just below the herniated tonsils. Sections are 0.5 cm apart. The peak velocity for the Chiari model is greater at the foramen magnum and increases less steeply with distance.

Axial sections showing flow velocity at the craniovertebral junction in the Chiari model at the time when flow direction changes from cranial to caudal (A) (t = 0.00 seconds) and when flow direction changes from caudal to cranial (B) (t = 0.50 seconds). C and D, For comparison, corresponding sections are also shown for the normal model at these times in the cycle. Note that oppositely directed flow is observed at the boundaries of the subarachnoid space (ie, there is synchronous bidirectional flow). The velocities are greater in the Chiari model. Velocity scales are the same as in A and B, respectively.

Sagittal plane sections showing pressure distributions along the cord in the Chiari model at the time when flow direction changes from cranial to caudal (A) (t = 0.00 seconds) and when flow direction changes from caudal to cranial (B) (t = 0.50 seconds). At these times, the pressure gradient along the cord is at its maximum. At the times of maximal caudal (C) (t = 0.25 seconds) and cranial (D) (t = 0.75 seconds) flow, the pressure gradient was at its minimum. Pressure scales are the same as in A and B, respectively.