Introduction
This topic covers hydrocephalus (hydrocephaly): an increase in the volume of cerebrospinal fluid (CSF) in the ventricles, with or without raised intracranial pressure. You should define it, recall CSF circulation, explain how each cause leads to it, and classify it, and then describe the brain changes and outcome.
Definition and CSF circulation
Hydrocephalus is an abnormal accumulation of CSF within the ventricular system (and sometimes the subarachnoid space) that enlarges the ventricles. It must be distinguished from hydrocephalus ex vacuo, in which the ventricles are enlarged only because brain tissue has been lost (atrophy, infarct) and CSF pressure is normal.
- CSF is formed mainly by the choroid plexus of the lateral, third and fourth ventricles (about 500 ml a day; total volume about 150 ml in adults).
- Route: lateral ventricles, interventricular foramina of Monro, third ventricle, cerebral aqueduct of Sylvius, fourth ventricle, foramina of Luschka and Magendie, subarachnoid space (cisterns, convexity), then absorption by arachnoid granulations into the superior sagittal sinus.