Hydrocephalus refers to the excess accumulation of CSF. This can occur because of obstruction of CSF flow, reduced absorption, or excess production. Most (70%) of CSF is produced by the choroid plexus and absorbed by the arachnoid villi and granulations. Flow direction is from the lateral ventricles to the third ventricle via the foramen of Monro. It then flows through the aqueduct of Sylvius to the fourth ventricles and exits via the foramina of Luschka and Magendie to the basal cisterns.1,2 It then divides between the spinal subarachnoid space and the subarachnoid cisterns. CSF is absorbed through arachnoid villi covering the brain and leptomeninges, across the ependymal lining of the ventricles, and the spinal subarachnoid space.1,2 Although there are several ways to categorize hydrocephalus based on the site of excess fluid collection, the primary concern in the emergency department is determining the etiology of the problem and instituting appropriate treatment.
Most cases of hydrocephalus result from congenital or acquired obstructions to the flow of CSF from the brain to the spinal canal. Congenital malformations include the Arnold–Chiari malformation, which is elongation and downward displacement of the brain stem into the fourth ventricle, and the Dandy–Walker malformation, which is a posterior fossa cyst that causes obstruction at the outlet of the fourth ventricle at the foramina of Luschka and Magendie.2 Neural tube defects such as myelomeningocele (spina bifida) usually result in hydrocephalus due to a Chiari malformation, obstruction of the fourth ventricle, or stenosis of the aqueduct of Sylvius (aqueductal stenosis).2 Intrauterine infections such as toxoplasmosis, rubella, cytomegalovirus, herpes, and syphilis can lead to hydrocephalus through inflammation of the ependymal lining of the ventricular system and lead to CSF flow obstruction. 1,2 Intraventricular hemorrhage in preterm newborns can also lead to hydrocephalus. Beyond the neonatal period, the most common causes of acquired hydrocephalus are mass lesions, which include tumors, cysts, and abscesses. Other acquired causes of hydrocephalus are meningitis, encephalitis, vascular malformations, or intracranial hemorrhage.1,2