Hydrocephalus

What it is

Hydrocephalus is obstruction to the flow of cerebrospinal fluid, leading to dilatation of the ventricular system proximal to the site of the obstruction. One form is set apart from the rest. Normal pressure hydrocephalus is a chronic communicating hydrocephalus that primarily affects adults over 60 years of age, in which reduced absorption of CSF leads to accumulation of CSF and enlargement of the ventricle, while the pressure stays normal or only mildly elevated. Its cause is idiopathic.

How it presents

In a child the signs are those of increased ICP, with sun setting eyes and a large head. In normal pressure hydrocephalus there is a triad instead. The gait goes first, with frequent falls and a broad-based gait of short shuffling steps, which is gait apraxia, also known as magnetic gait. Then dementia, and urinary incontinence. Normal pressure hydrocephalus does not show the signs of increased ICP, so there is no headache and no papilledema.

Causes and risk

Hydrocephalus is met as part of other conditions more often than on its own. Congenital toxoplasmosis holds it in its triad with chorioretinitis and intracranial calcifications. In spina bifida, Arnold-Chiari malformation is described as cerebellar hypoplasia with hydrocephalus and weakness of the face and swallowing, associated with limb deformity as well. It is also listed as a feature of the progressive deforming type of osteogenesis imperfecta. The causes are listed in two groups, and the group decides the name. Non-communicating hydrocephalus, an obstruction in the ventricular system, comes from congenital malformation such as aqueduct stenosis, atresia of the outflow foramina of the fourth ventricle in Dandy-Walker malformation, and Chiari malformation, and also from posterior fossa neoplasm or vascular malformation and from intraventricular haemorrhage in the preterm infant. Communicating hydrocephalus, a failure to reabsorb CSF, comes from subarachnoid haemorrhage and from meningitis, for example pneumococcal or tuberculous. Some causes can give either picture.