If there is hemorrhaging in the brain, blood may collect here. Adults tend to bleed here as a result of closed head injury. The subdural space is another potential space that may exist between the dura mater and the medial layer of the meninges, the arachnoid mater. When bleeding occurs in the cranium, blood may collect here and push down on the lower layers of the meninges. If bleeding continues, brain damage will result from this pressure.
Children are especially likely to have bleeding in the subdural space in cases of head injury.
The arachnoid or arachnoid mater is the middle layer of the meninges. In some areas, it projects into the sinuses formed by the dura mater. These projections are the arachnoid granulations or villi . They transfer cerebrospinal fluid, the fluid found in the ventricles, back into the bloodstream. The subarchanoid space lies between the arachnoid and pia mater.