Volumetric analysis of syringomyelia following hindbrain decompression for Chiari malformation Type I: syringomyelia resolution follows exponential kinetics

Abstract

Object: Resolution of syringomyelia is common following hindbrain decompression for Chiari malformation, yet little is known about the kinetics governing this process. The authors sought to establish the volumetric rate of syringomyelia resolution.

Methods: A retrospective cohort of patients undergoing hindbrain decompression for a Chiari malformation Type I with preoperative cervical or thoracic syringomyelia was identified. Patients were included in the study if they had at least 3 neuroimaging studies that detailed the entirety of their preoperative syringomyelia over a minimum of 6 months postoperatively. The authors reconstructed the MR images in 3 dimensions and calculated the volume of the syringomyelia. They plotted the syringomyelia volume over time and constructed regression models using the method of least squares. The Akaike information criterion and Bayesian information criterion were used to calculate the relative goodness of fit. The coefficients of determination R(2) (unadjusted and adjusted) were calculated to describe the proportion of variability in each individual data set accounted for by the statistical model.

Results: Two patients were identified as meeting inclusion criteria. Plots of the least-squares best fit were identified as 4.01459e(-0.0180804)(x) and 13.2556e(-0.00615859)(x). Decay of the syringomyelia followed an exponential model in both patients (R(2) = 0.989582 and 0.948864).

Conclusions: Three-dimensional analysis of syringomyelia resolution over time enables the kinetics to be estimated. This technique is yet to be validated in a large cohort. Because syringomyelia is the final common pathway for a number of different pathological processes, it is possible that this exponential only applies to syringomyelia related to treatment of Chiari malformation Type I.

Fig. 1

Region of interest selection. Using OsiriX software, we identified the syringomyelia as the region of interest.

Fig. 2

Three-dimensional reconstruction. Using consecutive regions of interest, a 3D volume was rendered and quantitatively calculated.

Fig. 3

Rate of syringomyelia decay. Plots of the least-squares best fit in Cases 1 (left) and 2 (right).×axis = number of days following surgery; y axis = syringomyelia volume (cm³). Left: Wolfram Alpha LLC. 2011. Wolfram|Alpha. http://www.wolframalpha.com/input/?i=exponential+fit+{0%2C+4.0147}%2C+{116%2C+0.4918}%2C+{513%2C0.3165}%2C+{676%2C0.2689} (Accessed July 14, 2011). Right: Wolfram Alpha LLC. 2011. Wolfram|Alpha. http://www.wolframalpha.com/input/?i=exponential+fit+{84%2C8.916}%2C+{135%2C+4.0665}%2C+{331%2C2.6985}%2C+{659%2C+0.8934} (Accessed July 14, 2011).