This suggests that the crowding of brain structures in the posterior fossa is due to an underdevelopment of the occipital bone, which in turn may result from an underdevelopment of the mesodermal occipital somite. Although the extent of tonsilar herniation does not correlate with the PFR, the age of the patients does. Patients with relatively smaller posterior fossas develop clinical symptoms at a younger age. Patients presenting with cough headache show a greater amplitude of pulsation and a greater reduction in the size of the subarachnoid space. However, the amplitude of pressure waves does not correlate with the presence of syringomyelia.
Flow is impaired during systole and unchanged during diastole.