One of the major issues associated with shunting the ventricles of elderly patients is the development of subdural collections due to a excessive reduction in ventricular volume ("overshunting") leading to a subdural "dead space" that can fill with acute blood (hematoma) from the stretching of vessels traversing the space, or bland fluid = hygroma. Differentiating hygroma from chronic hematoma is always difficult on CT. The presence of membranes (granulation tissue) in the fluid indicates old hematoma but they can be very hard to see.