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Research Papers

Cerebrospinal Fluid Flow Impedance is Elevated in Type I Chiari Malformation

[+] Author and Article Information
Nicholas Shaffer, Bryn A. Martin

Conquer Chiari Research Center,
Department of Mechanical Engineering,
University of Akron,
Akron, OH 44325-0406

Brandon Rocque, Casey Madura, Bermans J. Iskandar

Department of Neurological Surgery,
University of Wisconsin,
Madison, WI 53792-8660

Oliver Wieben

Departments of Radiology and Medical Physics,
University of Wisconsin,
Madison, WI 53705-2275

Stephen Dombrowski, Mark Luciano

Department of Neurological Surgery,
Cleveland Clinic Foundation,
Cleveland, OH 44195

John N. Oshinski

Department of Radiology and Imaging Sciences,
Emory University School of Medicine,
Atlanta, GA 30322

Francis Loth

Conquer Chiari Research Center,
Department of Mechanical Engineering,
University of Akron,
Akron, OH 44325-0406
email: loth@uakron.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received September 1, 2013; final manuscript received December 16, 2013; accepted manuscript posted December 23, 2013; published online February 5, 2014. Editor: Victor H. Barocas.

J Biomech Eng 136(2), 021012 (Feb 05, 2014) (8 pages) Paper No: BIO-13-1402; doi: 10.1115/1.4026316 History: Received September 01, 2013; Revised December 16, 2013; Accepted December 23, 2013

Diagnosis of Type I Chiari malformation (CMI) is difficult because the most commonly used diagnostic criterion, cerebellar tonsillar herniation (CTH) greater than 3–5 mm past the foramen magnum, has been found to have little correlation with patient symptom severity. Thus, there is a need to identify new objective measurement(s) to help quantify CMI severity. This study investigated longitudinal impedance (LI) as a parameter to assess CMI in terms of impedance to cerebrospinal fluid motion near the craniovertebral junction. LI was assessed in CMI patients (N = 15) and age-matched healthy controls (N = 8) using computational fluid dynamics based on subject-specific magnetic resonance imaging (MRI) measurements of the cervical spinal subarachnoid space. In addition, CTH was measured for each subject. Mean LI in the CMI group (551 ± 66 dyn/cm5) was significantly higher than in controls (220 ± 17 dyn/cm5, p < 0.001). Mean CTH in the CMI group was 9.0 ± 1.1 mm compared to −0.4 ± 0.5 mm in controls. Regression analysis of LI versus CTH found a weak relationship (R2 = 0.46, p < 0.001), demonstrating that CTH was not a good indicator of the impedance to CSF motion caused by cerebellar herniation. These results showed that CSF flow impedance was elevated in CMI patients and that LI provides different information than a standard CTH measurement. Further research is necessary to determine if LI can be useful in CMI patient diagnosis.

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Figures

Grahic Jump Location
Fig. 1

(a) Midsagittal MRI image of the cervical spine of a CMI patient showing the McRae line, CTH measurement (approximately 7.4 mm for this case), and planes where pressure drop was calculated; (b) transverse MRI image from the plane used to demarcate the model top, highlighting the separation between the cerebellar tonsils and body of the cerebellum. Note: patient tonsils for this case are asymmetric with greater CTH on the left side.

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Fig. 2

CTH as a function of age (in decade range, e.g., first decade 0–10 y) and sex for healthy subjects showing a parabolic trend with females having greater CTH values throughout life. Positive CTH values are in the caudal direction to the FM (data based on Smith et al. [8]). CMI patients, not shown, would have positive CTH values greater than 3 mm.

Grahic Jump Location
Fig. 3

(a) CSF flow waveforms (Q#) from five different subjects and (b) example waveform with modified properties used to demonstrate that LI values (c and d), integrated from the sum of ZL values on the y-axis, were independent of flow waveform shape over the range of frequencies analyzed (A and f represent waveform amplitude and frequency, respectively)

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Fig. 4

(a) Distribution and (b) data spread of LI compared with (c) distribution and (d) data spread of CTH for the healthy volunteers (HV) and CMI patients (CMI). Note, + indicates a statistical outlier in (a) and (c); the order of data points in (b) and (d) is identical.

Grahic Jump Location
Fig. 5

Relationship between CTH and LI is shown to be weakly correlated. The red line denotes the 3 mm minimum cutoff above which a subject would typically be considered anatomically positive for CMI.

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Fig. 6

(a) Midsagittal MRI image for an (a) asymptomatic CMI patient and (b) symptomatic CMI patient and (c and d) 3D models for each, respectively. CTH was similar for the two cases. However, LI in the symptomatic patient was 4.2 times greater than the asymptomatic patient.

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