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Evaluating Tonsil, Spinal Cord and CSF Motion in Symptomatic and Asymptomatic Patients with Chiari I Malformation. 2007

General Spine

Joseph P Cousins, Ph.D., M.D.
Victor Haughton, M.D., Non ASSR Member

Scientific Paper

Purpose

Chiari I malformation poses a diagnostic dilemma for both the clinician and spine radiologist. The goal of imaging is to determine which patients may benefit from intervention and those which would not. About a third of patients with tonsillar ectopia do not have symptoms referable to the malformation. The pathogenesis of syringomyelia in the symptomatic patients is not known. The Gardner "water hammer" hypothesis (1) that CSF is forced into the central spinal canal because of anomalous development of the obex has been abandoned. Ball and Dayan hypothesize that the CSF is driven into the Virchow-Robin spaces of the spinal cord when the spinal subarachnoid pressure is increased, especially during coughing or straining (2). Heiss et al. postulate that a piston-like movement of the herniated tonsils produces downward pulse waves in the subarachnoid space, which force water into the spinal cord (3). Stoodley et al. (4) suggest that altered compliance in the spinal subarachnoid space increases CSF flow into the Virchow-Robin space. To reconcile some these different theories, we have begun studies of CSF flow, spinal cord and tonsilar movement with new and conventional gated MR imaging.

Methods & Materials

For this study, Chiari I patients are characterized independently by a specialist on the basis of conventional clinical criteria into symptomatic or asymptomatic Chiari I malformations. Tonsilar motion is evaluated with a sagittal cardiac gated 2D FIESTA sequence and a five slice axial PC MR acquisition through the foramen magnum and cerebellar tonsils. The MR protocol includes: Sagittal T1 FLAIR, propeller axial T2, coronal T2 FLAIR, diffusion-weighted series and axial T1 3-D SPGR. CSF flow through the foramen magnum is evaluated with cardiac gated sagittal T2 FRFSE, sagittal cine phase contrast, axial fast-card PC using single slice and multislice technique. Volunteers without CNS pathology or cervical cord symptoms have been recruited as control subjects. The study has been approved by the local internal review board.

Results

The spinal cord and tonsils demonstrate no motion through most of the cardiac cycle. At one point during systole the cord moves downward with a velocity of about 1 mm/sec and at one point during diastole it moves upward with about the same velocity. Displacement of the tonsils, evaluated by 2D FIESTA is about 1 mm which is best appreciated on the cine loops. (Images 1 and 2 show the maximum and minimun tonsilar displacement in a Chiari I patient.) Velocities of the CSF exceed those of the cord and tonsils by an order of magnitude. Differences in the displacement of tonsils between the two patient groups and the controls are small.

Conclusion

Movement of the cerebellar tonsils does not appear sufficient to generate a pressure wave. Tonsilar and spinal cord motion may not be a significant factor in the pathogenesis of neurologic signs and symptoms in the Chiari I malformation.

References

(1) Gardner WJ, Angel J. The cause of syringomyelia and its surgical treatment. Cleve Clin Q 1958;25:4-8.
(2) Ball MJ, Dayan AD. Pathogenesis of syringomyelia. Lancet 1972;ii:799-801.
(3) Heiss JD, Patronas N, DeVroom HL, et al. Elucidating the pathophysiology of syringomyelia. J Neurosurg 1999;91:553-62.
(4) Stoodley MA, Brown SA, Brown CJ, et al. Arterial pulsation-dependent perivascular cerebrospinal fluid flow into the central canal in the sheep spinal cord. J Neurosurg 1997;86:686-93

The authors have no financial interests which require disclosure.

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