title: Effect of tonsillar herniation on cyclic CSF flow studied with computational flow analysis.
abstract: OBJECTIVE
  The Chiari I malformation, characterized by tonsils extending below the foramen magnum, has increased CSF velocities compared with those in healthy subjects. Measuring the effect of tonsillar herniation on CSF flow in humans is confounded by interindividual variation. The goal of this study was to determine the effect of herniated tonsils on flow velocity and pressure dynamics by using 3D computational models.
  
  
  METHODS
  A previously described 3D mathematic model of the normal subarachnoid space was modified by extending the tonsils inferiorly. The chamber created was compared with the anatomy of the subarachnoid space. Pressures and velocities were calculated by CFA methods for sinusoidal flow of a Newtonian fluid. Results were displayed as 2D color-coded plots and 3D animations. Pressure gradients and flow velocities were compared with those in the normal model. Velocity distributions were also compared with those in clinical images of CSF flow.
  
  
  RESULTS
  The model represented grossly the subarachnoid space of a patient with Chiari I malformation. Fluid flow patterns in the Chiari model were complex, with jets in some locations and stagnant flow in others. Flow jets, synchronous bidirectional flow, and pressure gradients were greater in the Chiari model than in the normal model. The distribution of flow velocities in the model corresponded well with those observed in clinical images of CSF flow in patients with Chiari I.
  
  
  CONCLUSIONS
  Tonsillar herniation per se increases the pressure gradients and the complexity of flow patterns associated with oscillatory CSF flow.
authors: Telemark University College, Porsgrunn, Norway. sveinlin@simula.no
authors: S O
authors: SO
authors: Linge
authors: V
authors: V
authors: Haughton
authors: A E
authors: AE
authors: Løvgren
authors: K A
authors: KA
authors: Mardal
authors: A
authors: A
authors: Helgeland
authors: H P
authors: HP
authors: Langtangen
references: Neurosurg Rev. 2006 Oct;29(4):251-63; discussion 264
references: 16752160
references: Neurosurg Rev. 2010 Jul;33(3):271-84; discussion 284-5
references: 20532585
references: Radiology. 2004 Jul;232(1):229-36
references: 15155896
references: AJNR Am J Neuroradiol. 2010 Jan;31(1):185-92
references: 19729542
references: Magn Reson Imaging Clin N Am. 1999 Aug;7(3):573-87
references: 10494536
references: IEEE Trans Vis Comput Graph. 2006 Nov-Dec;12(6):1535-46
references: 17073375
references: AJNR Am J Neuroradiol. 2004 Jan;25(1):142-5
references: 14729545
references: J Neurosurg. 1994 Jan;80(1):3-15
references: 8271018
references: J Neurosurg. 1999 Oct;91(4):553-62
references: 10507374
references: AJNR Am J Neuroradiol. 2006 Feb;27(2):354-5
references: 16484409