hydrocephalus An abnormal buildup of cerebrospinal fluid (CSF) in the ventricles and/or subarachnoid space of the brain. The fluid often increases intracranial pressure, which can compress and damage the brain. Hydrocephalus can arise before birth or at any time afterward. Causes can include birth defects (particularly spina bifida), hemorrhage into the brain, infection, meningitis, tumor,…
hydrocephalus, acquired Hydrocephalus that is due to a postnatal cause, something that happened sometime after birth. See also hydrocephalus.
hydrocephalus, communicating Hydrocephalus in which there is no obstruction to the flow of the cerebrospinal fluid (CSF). Specifically, there is no obstruction within the ventricular system of the brain or where the CSF passes into the spinal canal. Communicating hydrocephalus is due to overproduction of CSF or failure of the brain to reabsorb CSF normally.
hydrocephalus, congenital Hydrocephalus that is present at birth. See also hydrocephalus.
hydrocephalus, normal pressure Hydrocephalus that occurs because of a gradual blockage of CSF drainage pathways in the brain. Although the ventricles enlarge, intracranial pressure remains within normal range. Abbreviated NPH. NPH can occur as a complication of brain infection or bleeding (hemorrhage). In some patients, no predisposing cause can be identified. NPH is characterized by…
hydrocephalus ex-vacuo Hydrocephalus that occurs when there is damage to the brain caused by stroke or injury, in which there may be an actual shrinkage of brain substance. The CSF pressure itself is normal. See also hydrocephalus; hydrocephalus, normal pressure.
hydrocephaly See hydrocephalus.
hydrogen breath test A test that uses the measurement of hydrogen in the breath to diagnose several conditions that cause gastrointestinal symptoms. Large amounts of hydrogen may be produced by anaerobic bacteria in the colon when there is a problem with the digestion or absorption of food in the small intestine that allows more unabsorbed…
hydronephrosis Distention of the kidney with urine. Hydronephrosis is caused by obstruction of urine outflow (for example, by a stone blocking the ureter).
hydrops fetalis A serious and potentially fatal condition of a fetus characterized by gross edema (swelling) from abnormal accumulation of fluids in the body. Hydrops fetalis has both immune-related and non-immune-related causes. Immune-related hydrops fetalis can be due to hemolytic disease such as Rh blood group incompatibility, in which antibodies crossing the placenta from the…
hydroxyapatite An essential ingredient of normal bone and teeth that makes up bone mineral and the matrix of teeth and gives them their rigidity. See also hydroxyapatite crystal disease.
hydroxyapatite crystal disease Inflammation caused by hydroxyapatite crystals. Hydroxyapatite molecules can group together (crystallize) to form microscopic clumps. If the tiny crystals of hydroxyapatite are deposited by mistake in or around joints, they may cause inflammation of the joints and nearby tissues, such as tendons and ligaments. Hydroxyapatite crystal disease is sometimes the cause of…