Commonly referred to as ‘water on the brain, and first described by Hippocrates of Chios (460-377 BP), it is a disorder in which there is an obstruction of cerebrospinal fluid, which then accumulates in the ventricles (internal or non-communicating hydrocephalus) or in the sub-arachnoid spaces (external or communicating hydrocephalus), leading to an increase in intracranial pressure. This results in an enlargement of the head (macrocephaly) in infants as their skull plates have not fused and bulging of the fontanelles, and to a wide range of impairments and disabilities (e.g., visual impairment, lack of growth, deafness, blindness, spastic quadriplegia). Most forms of hydrocephalus require treatment, the most common one being a shunting device. This device, surgically inserted so that the upper end is in a ventricle and the lower end in the heart or abdomen, consists of a system of tubes with a valve to control the rate of drainage and prevent back flow. Fluid drained into the abdomen passes into the bloodstream. Congenital hydrocephalus affects about one in every 1000 births, with the overall prevalence in the US being about 0.5%. Preterm infants are particularly at risk of developing hydrocephalus as the blood vessels of the area just beneath the lining of the ventricles are very fragile and can easily rupture, leading to a brain haemorrhage, which can cause a blockage. Hydrocephalus is also associated, for example, with meningitis and spina bifida. It effects vary from one individual to another, and some people will have very few, if any, problems. Perhaps the best-known example in this respect is the case of the maths student with hydrocephalus at the University of Sheffield who had an IQ of 126 and a normal social life, and graduated with a first-class honours degree, despite having only 10% of normal brain tissue as revealed by a CAT scan carried out under the supervision of the neurologist Richard Lorber who has reported other such cases. His work, which was taken to indicate the enormous redundancy of much of the human brain, was criticized by others for supposed methodological shortcomings.
See Anterior fontanelle, Birth prevalence, Brain (neuro-) imaging, Cerebrospinal fluid (CSF), Chiari II malformation, Congenital malformations, Meninges, Meningitis, Preterm infant, Spastic quadriplegia, Spina bifida, Stimulus generalization, Ventricle