Ventricular dilation and elevated aqueductal pulsations in a new experimental model of communicating hydrocephalus

In communicating hydrocephalus (CH), explanations for the symptoms and clear-cut effective treatments remain elusive. Pulsatile flow through the cerebral aqueduct is often significantly elevated, but a clear link between abnormal pulsations and ventriculomegaly has yet to be identified. We sought to demonstrate measurement of pulsatile aqueductal flow of CSF in the rat, and to characterize the temporal changes in CSF pulsations in a new model of CH. Hydrocephalus was induced by injection of kaolin into the basal cisterns of adult rats (n = 18). Ventricular volume and aqueductal pulsations were measured on a 9.4 T MRI over a one month period. Half of the animals developed ventricular dilation, with increased ventricular volume and pulsations as early as one day post-induction, and marked chronic elevations compared to intact controls (volume: 130.15 +/- 83.21 microl vs. 15.52 +/- 2.00 microl; pulsations: 114.51 nl +/- 106.29 vs. 0.72 +/- 0.13 nl). Similar to the clinical presentation, the relationship between ventricular size and pulsations was quite variable. However, the pulsation time-course revealed two distinct sub-types of hydrocephalic animals: those with markedly elevated pulsations which persisted over time, and those with mildly elevated pulsations which returned to near normal levels after one week. These groups were associated with severe and mild ventriculomegaly respectively. Thus, aqueductal flow can be measured in the rat using high-field MRI and basal cistern-induced CH is associated with an immediate change in CSF pulsatility. At the same time, our results highlight the complex nature of aqueductal pulsation and its relationship to ventricular dilation.