Magnetic resonance imaging measures of posterior cranial fossa morphology and cerebrospinal fluid physiology in Chiari malformation type I

Abstract

Background: It has been well documented that, along with tonsillar herniation, Chiari Malformation Type I (CMI) is associated with smaller posterior cranial fossa (PCF) and altered cerebrospinal fluid (CSF) flow and tissue motion in the craniocervical junction.

Objective: This study assesses the relationship between PCF volumetry and CSF and tissue dynamics toward a combined imaging-based morphological-physiological characterization of CMI. Multivariate analysis is used to identify the subset of parameters that best discriminates CMI from a healthy cohort.

Methods: Eleven length and volumetric measures of PCF, including crowdedness and 4th ventricle volume, 4 measures of CSF and cord motion in the craniocervical junction, and 5 global intracranial measures, including intracranial compliance and pressure, were measured by magnetic resonance imaging (MRI) in 36 symptomatic CMI subjects (28 female, 37 ± 11 years) and 37 control subjects (24 female, 36 ± 12 years). The CMI group was further divided based on symptomatology into "typical" and "atypical" subgroups.

Results: Ten of the 20 morphologic and physiologic measures were significantly different between the CMI and the control cohorts. These parameters also had less variability and stronger significance in the typical CMI compared with the atypical. The measures with the most significance were clival and supraocciput lengths, PCF crowdedness, normalized PCF volume, 4th ventricle volume, maximal cord displacement (P < .001), and MR measure of intracranial pressure (P = .007). Multivariate testing identified cord displacement, PCF crowdedness, and normalized PCF as the strongest discriminator subset between CMI and controls. MR measure of intracranial pressure was higher in the typical CMI cohort compared with the atypical.

Conclusion: The identified 10 complementing morphological and physiological measures provide a more complete and symptomatology-relevant characterization of CMI than tonsillar herniation alone.

Figure 1

A) The linear measures of the PCF: Clivus, supraocciput, McRae’s line, and Twining’s line, superimposed on mid-sagittal slices of 3-D T1-weighted MR images. B) A rendering of the automated PCF volume segmentation.

Figure 2

Measurements of cord motion dynamics. A) The imaging plane superimposed on the MRI mid-sagittal image in a CMI patient. (B) The cord region of interest superimposed on the MRI phase contrast velocity image. C) Average cord velocity waveforms for a representative CMI and control patient. D) Cord displacement waveforms from the representative CMI and control patient obtained by integration of the velocity waveforms with respect to time for one cardiac cycle.

Figure 3

Association between clivus and supraocciput length measurements. Linear regressions for the CMI (diamonds) and control (circles) cohorts do not show statistical significance.