A
- Acquired hydrocephalus
- Hydrocephalus that develops at some point after birth, often after an injury, bleed, infection, or tumor.
- Aqueduct of Sylvius (cerebral aqueduct)
- A narrow channel deep in the brain that connects the third ventricle to the fourth ventricle. A common site of obstruction in hydrocephalus.
- Aqueductal stenosis
- Narrowing of the cerebral aqueduct. One of the most common causes of obstructive hydrocephalus in children.
- Aquaporin
- A type of channel in cell membranes that lets water move in and out. Aquaporins are part of why the brain is permeable to water and play a role in some current research models of hydrocephalus.
- Arachnoid granulations (villi)
- Small structures that absorb cerebrospinal fluid back into the bloodstream.
- Arrested hydrocephalus
- A term sometimes used when the ventricles are enlarged but the condition appears to have stopped progressing without active treatment.
B
- Blood-brain barrier
- A protective layer of cells lining the small blood vessels in the brain that controls which substances can move between the blood and the brain.
C
- Catheter
- A thin, soft tube used in a shunt to move CSF from one part of the body to another.
- Cerebrospinal fluid (CSF)
- The clear, watery fluid that surrounds the brain and spinal cord. Produced in the ventricles, it cushions the brain and helps carry nutrients in and waste out.
- Choroid plexus
- Tissue inside the ventricles that produces most of the brain's cerebrospinal fluid.
- Communicating hydrocephalus
- A type of hydrocephalus in which CSF can still move freely between the ventricles, but is not being absorbed properly or is being acted on by other forces (for example, osmotic pull from macromolecules).
- Congenital hydrocephalus
- Hydrocephalus that is present at birth.
- CT (computed tomography)
- An imaging test that uses X-rays to make cross-sectional pictures of the brain. Faster than MRI, but uses radiation.
D
- Distal catheter
- The longer part of a shunt that runs under the skin from the valve to wherever the fluid is being drained (most often the abdomen).
E
- Efflux transporter
- A protein in cell membranes that pumps molecules out of cells. In the brain, efflux transporters help clear macromolecules from CSF. P-glycoprotein is a key example.
- Endoscope
- A thin, flexible instrument with a small camera, used to look inside the body. In neurosurgery, an endoscope can be used to operate inside the ventricles through a small opening.
- Endoscopic third ventriculostomy (ETV)
- A surgery in which the neurosurgeon creates a new opening in the floor of the third ventricle, allowing CSF to bypass a blockage. No device is implanted.
- ETV + CPC
- A combined procedure: endoscopic third ventriculostomy plus cauterization of the choroid plexus. Sometimes used in infants to improve success rates.
- Ex vacuo hydrocephalus
- Ventricles that look enlarged on imaging because the surrounding brain has shrunk — not because of too much CSF. Not true hydrocephalus, and generally not treated by shunting.
F
- Fontanelle
- The "soft spot" on a baby's head, where the skull bones have not yet fused. Useful for ultrasound imaging of the brain and as a clinical sign of pressure inside the head.
- Fourth ventricle
- The lowest of the four brain ventricles, located near the brainstem.
H
- Hydrocephalus
- A build-up of cerebrospinal fluid inside the brain, leading to enlargement of the ventricles and, often, increased pressure.
- Hyperosmolar
- Containing more dissolved particles than usual. Hyperosmolar CSF can pull water in by osmosis.
I
- Intracranial pressure (ICP)
- The pressure inside the skull. Elevated ICP can damage the brain and is one of the things hydrocephalus treatment aims to control.
- Intraventricular hemorrhage (IVH)
- Bleeding inside the ventricles. A common cause of acquired hydrocephalus, particularly in premature infants.
L
- Lumbar puncture (spinal tap)
- A procedure in which a thin needle is inserted into the lower back to sample or remove CSF, or to measure CSF pressure.
- Lumboperitoneal (LP) shunt
- A shunt that drains CSF from the spinal canal in the lower back to the abdomen. Sometimes used for communicating hydrocephalus, including some cases of NPH.
M
- Macromolecule
- A large molecule, such as a protein. The accumulation of macromolecules in CSF may pull water into the ventricles and is a focus of current research into the causes of hydrocephalus.
- MRI (magnetic resonance imaging)
- An imaging test that uses strong magnets and radio waves to make detailed pictures of the brain. Does not use radiation.
- Myelomeningocele
- The open form of spina bifida. Many babies with myelomeningocele also develop hydrocephalus.
N
- Neurosurgeon
- A surgeon who operates on the brain, spine, and nervous system. A pediatric neurosurgeon specializes in caring for children.
- Non-communicating (obstructive) hydrocephalus
- A type of hydrocephalus in which something — like a narrowed aqueduct, a cyst, or a tumor — is physically blocking the flow of CSF.
- Normal pressure hydrocephalus (NPH)
- A form of hydrocephalus that mainly affects adults over 60. The pressure measured on a spinal tap is often normal even though the ventricles are enlarged. Classic signs are trouble walking, urinary changes, and trouble with thinking.
O
- Osmosis
- The movement of water across a barrier toward a higher concentration of dissolved particles. A key mechanism in current research models of hydrocephalus.
- Osmotic gradient
- A difference in dissolved-particle concentration that causes water to move from one place to another.
P
- P-glycoprotein
- An efflux transporter that helps clear molecules out of the brain. Variation in p-glycoprotein activity is one possible explanation for why some patients develop hydrocephalus after a brain bleed and others do not.
- Phase-contrast MRI (CSF flow study, cine MRI)
- A special MRI technique that shows CSF in motion. Helps tell the difference between communicating and non-communicating hydrocephalus.
- Post-hemorrhagic hydrocephalus
- Hydrocephalus that develops after bleeding inside or around the brain. A common cause in premature infants.
- Programmable valve
- A shunt valve whose pressure setting can be adjusted from outside the body using a magnet, without surgery.
- Proximal catheter
- The part of a shunt that sits inside one of the ventricles, where it collects CSF.
R
- Reservoir
- A small dome on a shunt, just under the scalp, that can be used to sample CSF or test shunt function.
- Revision (shunt revision)
- A surgery to replace part or all of a shunt, often because it has become blocked, broken, infected, or outgrown.
S
- Shunt
- A small implanted device that drains excess CSF from a ventricle to another part of the body where it can be absorbed.
- Spina bifida
- A birth defect in which the spinal column does not close completely. The open form (myelomeningocele) is often associated with hydrocephalus.
- "Sunsetting" eyes
- A clinical sign in infants in which the eyes appear to look downward, with the white of the eye visible above the iris. Associated with raised pressure inside the head.
T
- Tap test (large-volume LP)
- A lumbar puncture in which a larger amount of CSF is removed to see whether symptoms — particularly walking — improve. Used in the workup of suspected NPH.
- Third ventricle
- One of the four brain ventricles, located in the center of the brain. The site of an ETV.
V
- Valve
- The part of a shunt that controls when and how fast CSF moves through. Can be fixed-pressure or programmable.
- Ventricle
- One of four fluid-filled spaces inside the brain. CSF is produced and circulates within the ventricles.
- Ventriculoatrial (VA) shunt
- A shunt that drains CSF from a ventricle into a large vein near the heart.
- Ventriculoperitoneal (VP) shunt
- The most common type of shunt. Drains CSF from a ventricle to the abdomen, where it is absorbed.
- Ventriculopleural shunt
- A shunt that drains CSF from a ventricle to the space around a lung.