Reversed aqueductal cerebrospinal fluid net flow in idiopathic normal pressure hydrocephalus.

OBJECTIVES: The changes of CSF flow dynamics in idiopathic normal pressure hydrocephalus (iNPH) are not fully elucidated. Most previous studies took the whole cardiac cycle as a unit. In this work, it is divided into systole and diastole phase and compared between iNPH patients and normal elderly and paid special attention to the change of netflow direction.

MATERIALS AND METHODS: Twenty iNPH patients according to international guideline and twenty healthy volunteers were included in this study and examined by MRI. Three categories of CSF flow parameters were measured: peak velocity (Vpeak ), stroke volume (SV), and minute flow volume (MinV) covering the whole cycle; peak velocity (Vpeak-s , Vpeak-d ) and flow volume (Vols , Vold ) of the systole and diastole, respectively; net flow. Evans index (EI) was also measured and compared statistically between the two groups.

RESULTS: EI, Vpeak , SV, MinV, Vols , Vold , and Vpeak-d significantly increased in iNPH group (P<0.05). Vpeak-s of the two groups were not significantly different (P>0.05). The net flow of 16 iNPH patients (16/20) was in the caudo-cranial direction, while 15 volunteers (15/20) were in the opposite direction, which showed statistically significant differences (P=.001).

CONCLUSIONS: INPH patients present hyperdynamic flow with increased velocity and volume both in systole and diastole phase. Degree of rising in diastole phase exceeds that of systole phase. The resulting reversal of netflow direction may play a key role in the occurrence of ventriculomegaly in iNPH patients.