Internal hydrocephalus, external hydrocephalus, and the syndrome of intracerebral cerebrospinal fluid entrapment: a challenge to current theories on the pathophysiology of communicating hydrocephalus.

The natural history of external hydrocephalus (EH) in adults is often marked by conversion into internal hydrocephalus. We describe a complication of this conversion, the ICE (intracerebral CSF entrapment) phenomenon, and demonstrate that both EH and ICE represent a challenge to current theories on the pathophysiology of communicating hydrocephalus (CHC). We propose a new model for CHC where the pattern of CSF distribution is largely determined by the intrinsic compliance of each of the intracranial structures. In this model, failure of distal CSF absorption resulting in an excessive intracranial CSF volume is the common denominator and CSF diversion the common solution to all forms of CHC.