Introduction

The ancient term hydrocephalus refers to an excessive accumulation of fluid (water) inside the head. It is most readily detected in infants and children with congenital hydrocephalus since its existence before the skull sutures are closed causes the formation of an enlarged head. Such children have long been recognized commonly to have mental impairment, manifest as mental retardation, although the extent of this is very variable. Morgagni (1769) first described hydrocephalus due to enlarged cerebral ventricles in an adult without head enlargement. If this condition develops insidiously during adult life, dementia is an almost invariable accompaniment, though not the only one. More familiarly hydrocephalus in adults develops acutely or subacutely and presents with symptoms of raised intracranial pressure – headache, vomiting and drowsiness. However, in this chapter we are concerned with chronic hydrocephalus in adults, a condition in which symptoms and signs of raised intracranial pressure are commonly clinically absent and in which the cerebrospinal fluid (CSF) pressure is often normal when measured randomly – hence the commonly used term – normal pressure hydrocephalus (NPH). The recognition of this condition, and the realization that it is responsible for some cases of progressive dementia in adults are recent (Riddoch, 1936; Foltz & Ward 1956; McHugh, 1964; Hakim & Adams, 1965; Adams et al., 1965). Cases of NPH, some of which respond well to a shunting procedure, are to be distinguished from cases of dementia due to neurodegenerative diseases in which the ventricles dilate as a consequence of cerebral atrophy (hydrocephalus ex vacuo).