Jan Malm and Anders Eklund are to be congratulated on their review of idiopathic normal pressure hydrocephalus (NPH) (

). The various theories of pathophysiology documented in their review are, however, unconvincing: how can mechanical compression of the brain parenchyma occur with normal sized ventricles and intracranial pressure? What is periventricular resorption of CSF and how does it cause reversible damage? What potentially toxic metabolites are present in CSF? What evidence is there for venous damage to the brain in this condition, and why should shunting reverse this? I should like to expound a simple, coherent explanation of the process based on information already in the public domain, largely summarised in Malm and Eklund’s …