Foramen magnum cerebrospinal fluid flow characteristics in children with Chiari I malformation before and after craniocervical decompression.

OBJECT: The Chiari I malformation presents significant challenges to clinicians because its pathophysiology is not well understood. In conducting cerebrospinal fluid (CSF) flow studies, investigators have attempted to correlate the clinical severity of these lesions with general flow velocity or bulk flow at the foramen magnum; however, these techniques have not allowed consistent prediction of symptomatology, explanation of the presence of syringomyelia, or the assessment of the hydrodynamic characteristics of the decompression. The authors used temporally and spatially resolved flow analyses to assess the characteristics of CSF flow in children with Chiari I malformation and the changes in these flow characteristics that occur after suboccipital decompression.

METHODS: The authors studied eight children with symptomatic Chiari I malformation with or without syringomyelia and two children without Chiari I malformation. All patients underwent phase-contrast magnetic resonance imaging before and after posterior fossa decompression. Velocity plots were displayed for each voxel. Several indices of CSF flow were developed to characterize the flow patterns associated with Chiari I malformation. In children with symptomatic Chiari I malformation, even though bulk flow or velocity is often normal, there was marked heterogeneity of flow at the foramen magnum. This was evident for several reasons: 1) an increase in cephalad and caudad peak velocities; 2) spatial inhomogeneity in velocities; 3) simultaneous bidirectional flow; and 4) substantial net craniad or caudad flows within particular voxels and subregions during the cardiac cycle. After posterior fossa decompression, the severity of these flow abnormalities decreased.

CONCLUSIONS: Foramen magnum CSF flow in children with symptomatic Chiari I malformations is spatially and temporally heterogeneous, and this heterogeneity improves postoperatively. The authors propose that relying on mean flow parameters in patients with Chiari I malformation is no longer sufficient; instead, more elaborate techniques to analyze foramen magnum CSF flow have become necessary.