The aim of this study was to determine CSF pressure and velocities in idealized geometries representing the stenosed spinal canal found in Chiari patients.We applied the Navier-Stokes equation to simulate the cyclic CSF flow during one cardiac cycle. Hereby, we have illuminated a well-established medical hypothesis for the relation between the Chiari I malformation and syringomyelia: namely that spinal cord cysts are caused by the so-called Venturi effect (predicted by Bernoulli's law) appearing in fluids that flow through obstructed areas. The results showed that the pressure gradient in geometries with obstructions comparable to Chiari patients may be 10 times as high as under normal flow conditions. The results also showed that the pressure gradients at the level of an obstruction may be twice as large as that predicted from steady flow or Bernoulli's law.