Hydrocephaly is a condition in which the flow and absorption of spinal fluid, which is manufactured inside the brain, is interrupted. Cerebrospinal fluid accumulates within skull. The head circumference may increase abnormally, and if untreated, brain damage may occur. It is due to one of three causes: (a) excessive production of cerebro-spinal fluid; (b) defective absorption of cerebro-spinal fluid; or (c) blockage of cerebro-spinal fluid. The causes of such disturbances may be congenital, meningitis, or a tumour.
Hydrocephaly may be present at birth or may develop even months after birth. It can be treated surgically by leading excess cerebro-spinal fluid away from the skill and, if brain development was not already impaired, neurological and mental development can be adequate. Prenatal infections may cause hydrocephaly in infants. There are genetic forms, either autosomal recessive or X-linked recessive, but generally the recurrence risk with later children is moderated. Hydrocephaly may also develop secondarily to birth trauma, notably after premature births.
Hydrocephaly averages around 2 to 4 births per 10,000. High rates are seen in Canada, USA and Sichuan, China. An increasing rate is seen in several monitoring centres around the world. A strongly declining trend is seen in England and Wales and Hungary. Variations in rate are probably partly due to the variability of definition of hydrocephaly and the length of time newborns are followed up. Prenatal diagnosis and selective abortion have probably played a role in the declining rates in Paris.