Hydrocephalus can be divided by location into intraventricular hydrocephalus and extraventricular hydrocephalus. The latter is also called externalhydrocephalus (eh). External hydrocephalus refers to an increase in fluid accumulation in the subarachnoid space within the skull, i.e., an excess accumulation of water in a space between the skull and brain tissue. Normally, there is a small amount of fluid in the subarachnoid space, and its amount remains constant because secretion and excretion are in dynamic balance. It occurs mainly in infancy and early childhood and only in children whose fontanelles are not closed. Any factor that causes damage to the central nervous system that arises during the perinatal period may lead to external hydrocephalus. These include asphyxia, obstructed labor, preterm birth, intracranial hemorrhage, and neonatal hyperbilirubinemia. Cranial trauma and infection are also important causes, as are lung infections and vitamin A toxicity or deficiency. However, in pathological conditions such as inflammation of the meninges and inflammation and hemorrhage of the blood vessels in the subarachnoid space, there is increased secretion or impaired drainage of cerebrospinal fluid resulting in retention of fluid in the subarachnoid space. In addition, in cases of frontal lobe atrophy or hypoplasia, there is an increase in fluid secondary to an enlarged subarachnoid space between the brain and the skull. External hydrocephalus differs from what is commonly referred to as congenital or inflammatory hydrocephalus, which is an increase in intracerebroventricular fluid accumulation that results in brain atrophy due to water compression of brain tissue, with a poor prognosis and mostly requiring surgical treatment. In contrast, external hydrocephalus is an outdoor type of hydrocephalus, which has a better prognosis and generally does not require surgical treatment.