Standard and Cardiac-Gated Phase-Contrast MRI in CM-I
Object The causal treatment of Chiari malformation Type I (CM-I) consists of removing the obstruction of CSF flow at the level of the foramen magnum. Cerebrospinal fluid flow can be visualized using dynamic phase-contrast MR imaging. Because there is only a paucity of studies evaluating CSF dynamics in the region of the spinal canal on the basis of preoperative and postoperative measurements, the authors investigated the clinical usefulness of cardiacgated phase-contrast MR imaging in patients with CM-I.
Methods Ninety patients with CM-I underwent preoperative MR imaging of CSF pulsation. Syringomyelia was present in 59 patients and absent in 31 patients. Phase-contrast MR imaging of the entire CNS was used to investigate 22 patients with CM-I before surgery and after a mean postoperative period of 12 months (median 12 months, range 3–33 months). In addition to the dynamic studies, absolute flow velocities, the extension of the syrinx, and tonsillar descent were also measured.
Results The changes in pulsation were highly significant in the region of the (enlarged) cistern (p = 0.0005). Maximum and minimum velocities (the pulsation amplitude) increased considerably in the region where the syrinx was largest in diameter. The changes of pulsation in these patients were significant in the subarachnoid space in all spinal segments but not in the syrinx itself and in the central canal.
Conclusions The demonstration of CSF flow pulsation can contribute to assessments of surgical outcomes. The results presented here, however, raise doubts about current theories on the pathogenesis of syringomyelia.
For decades it was assumed in the literature that patients with CM-I were a homogenous group. Milhorat, however, defined 5 subtypes of CM-I associated with different causative factors: 1) constriction of the posterior cranial fossa occurring with classic CM-I; 2) downward traction of the spinal cord occurring with tethered cord syndrome and occult tethered cord syndrome; 3) hypermobility of the atlantooccipital and atlantoaxial joints; 4) increased intracranial pressure; and 5) intraspinal hypotension. Yet there is general agreement that the most common cause of CM-I is a smaller than normal posterior fossa volume.
Because impaired CSF pulsations are an essential precondition for the development of syringomyelia, their visualization and quantification play a crucial role in the understanding of individual cases and the planning of causal treatment. In the past, a number of different MR imaging techniques have been developed and described that allow CSF movement to be assessed in terms of velocity and direction. At present, the most commonly used technique is cardiac-gated phase-contrast MR imaging. In the 1990s, this method was introduced and established primarily for investigations of the brain by Quencer et al., Levy et al., and Nitz and colleagues—as well as by Schroth and Klose in Germany—and has been verified in several studies. This method allows MR images of CSF flow to be displayed in a cine mode throughout the cardiac cycle.
Although the international literature reports that dynamic phase-contrast MR imaging is the standard method for diagnosing patients with CM-I, it is a technique that is not routinely used in clinical practice. The visualization of CSF flow in the region of the cerebrum has been studied extensively and analyzed in a structured manner. There is, however, a paucity of structured studies evaluating CSF dynamics in the region of the spinal canal in a reasonable number of patients. For this reason, we investigated the clinical usefulness of cardiac-gated phase-contrast MR imaging for the visualization of CSF flow in the spinal canal of patients with CM-I and assessed absolute CSF flow velocities, in particular postoperative changes.
Abstract and Introduction
Abstract
Object The causal treatment of Chiari malformation Type I (CM-I) consists of removing the obstruction of CSF flow at the level of the foramen magnum. Cerebrospinal fluid flow can be visualized using dynamic phase-contrast MR imaging. Because there is only a paucity of studies evaluating CSF dynamics in the region of the spinal canal on the basis of preoperative and postoperative measurements, the authors investigated the clinical usefulness of cardiacgated phase-contrast MR imaging in patients with CM-I.
Methods Ninety patients with CM-I underwent preoperative MR imaging of CSF pulsation. Syringomyelia was present in 59 patients and absent in 31 patients. Phase-contrast MR imaging of the entire CNS was used to investigate 22 patients with CM-I before surgery and after a mean postoperative period of 12 months (median 12 months, range 3–33 months). In addition to the dynamic studies, absolute flow velocities, the extension of the syrinx, and tonsillar descent were also measured.
Results The changes in pulsation were highly significant in the region of the (enlarged) cistern (p = 0.0005). Maximum and minimum velocities (the pulsation amplitude) increased considerably in the region where the syrinx was largest in diameter. The changes of pulsation in these patients were significant in the subarachnoid space in all spinal segments but not in the syrinx itself and in the central canal.
Conclusions The demonstration of CSF flow pulsation can contribute to assessments of surgical outcomes. The results presented here, however, raise doubts about current theories on the pathogenesis of syringomyelia.
Introduction
For decades it was assumed in the literature that patients with CM-I were a homogenous group. Milhorat, however, defined 5 subtypes of CM-I associated with different causative factors: 1) constriction of the posterior cranial fossa occurring with classic CM-I; 2) downward traction of the spinal cord occurring with tethered cord syndrome and occult tethered cord syndrome; 3) hypermobility of the atlantooccipital and atlantoaxial joints; 4) increased intracranial pressure; and 5) intraspinal hypotension. Yet there is general agreement that the most common cause of CM-I is a smaller than normal posterior fossa volume.
Because impaired CSF pulsations are an essential precondition for the development of syringomyelia, their visualization and quantification play a crucial role in the understanding of individual cases and the planning of causal treatment. In the past, a number of different MR imaging techniques have been developed and described that allow CSF movement to be assessed in terms of velocity and direction. At present, the most commonly used technique is cardiac-gated phase-contrast MR imaging. In the 1990s, this method was introduced and established primarily for investigations of the brain by Quencer et al., Levy et al., and Nitz and colleagues—as well as by Schroth and Klose in Germany—and has been verified in several studies. This method allows MR images of CSF flow to be displayed in a cine mode throughout the cardiac cycle.
Although the international literature reports that dynamic phase-contrast MR imaging is the standard method for diagnosing patients with CM-I, it is a technique that is not routinely used in clinical practice. The visualization of CSF flow in the region of the cerebrum has been studied extensively and analyzed in a structured manner. There is, however, a paucity of structured studies evaluating CSF dynamics in the region of the spinal canal in a reasonable number of patients. For this reason, we investigated the clinical usefulness of cardiac-gated phase-contrast MR imaging for the visualization of CSF flow in the spinal canal of patients with CM-I and assessed absolute CSF flow velocities, in particular postoperative changes.