PFD, C1 laminectomy, and duraplasty for the treatment of Chiari I malformation may lead to a more reliable reduction in the volume of concomitant hydromyelia, compared with PFD and C1 laminectomy alone. However, there seems to be a subset of patients whose symptoms will resolve and whose hydromyelic cavity will decrease with the removal of bone only. These patients seem to undergo a volumetric increase in the posterior fossa. Further studies are needed to better characterize these patients, to determine which patients with Chiari I malformation are better served with bony decompression only, and which will require duraplasty to resolve their hydromyelia.