To appreciate the condition, an understanding of the dynamics of CSF and the relationship between the various structures that make up the ventricular and subarachnoid spaces is necessary (Fig. 11-4) The two mechanisms by which CSF is formed include secretion by the choroid plexuses and lymphatic-like drainage by the extracellular fluid of the brain. CSF circulates throughout the ventricular system and is than absorbed within the subarachnoid spaces by a mechanism that is not entirely clear.