Hydrocephalus
How CSF is made, flows and is absorbed; why a block in the ventricles or failed absorption makes them swell; how hydrocephalus differs in infants, adults and older people with normal pressure; what only looks like it; and how shunts and ventriculostomy work.
By the end, you can
- Describe how CSF is produced, where it flows and how it is absorbed, and why production continues when pressure rises.
- Distinguish obstructive (non-communicating) from communicating hydrocephalus, and relate aqueduct stenosis, Chiari II and Dandy–Walker malformations, tumours, meningitis and subarachnoid haemorrhage to the site of the problem.
- Explain how hydrocephalus presents in infants, whose skull can still enlarge, compared with older children and adults, and explain the triad of normal-pressure hydrocephalus.
- Distinguish true hydrocephalus from hydrocephalus ex vacuo, in which ventricles enlarge to fill space left by lost brain.
- Recognise the classic appearances and tests of hydrocephalus, and explain how shunts and endoscopic third ventriculostomy act on the mechanism.
What it is
Hydrocephalus is an abnormal build-up of cerebrospinal fluid (CSF) that enlarges the ventricles, usually with raised pressure, because CSF cannot flow out of the ventricles (obstructive or non-communicating hydrocephalus) or is not absorbed once it reaches the subarachnoid space (communicating hydrocephalus). Normal-pressure hydrocephalus is a chronic communicating form of older adults. Ventricles that enlarge only to fill space left by lost brain tissue (hydrocephalus ex vacuo) are not true hydrocephalus.
4 types to tell apart
- Obstructive (non-communicating)
- Flow is blocked inside the ventricular system or at the outlets of the fourth ventricle: aqueduct stenosis, Chiari II and Dandy–Walker malformations, tumours, cysts and clot.
- Communicating
- CSF reaches the subarachnoid space but is not absorbed, usually after meningitis or subarachnoid or intraventricular haemorrhage, which clog and scar the arachnoid and its granulations.
- Normal-pressure hydrocephalus
- Older adults: enlarged ventricles with a normal pressure at lumbar puncture, causing gait disturbance, urinary incontinence and cognitive slowing.
- Congenital and acquired
- Present at birth, often with malformations, fetal infection or haemorrhage; or developing later after tumours, haemorrhage, infection or injury.
US spelling: litre → liter.
Normal function
Making, moving and absorbing CSF
CSF is made mainly by the , fronds of capillaries covered by specialised ependymal cells in each ventricle. These cells actively secrete sodium, chloride and bicarbonate into the ventricle, and water follows: about half a litre a day in adults, while only about 150 mL is present at any time, so the whole volume is replaced several times a day. Secretion is nearly constant and barely falls when pressure rises, which is why a blocked outflow fills the ventricles.
CSF flows from each through an into the , then through the narrow into the . It leaves the fourth ventricle through three openings, one median and two lateral apertures, into the subarachnoid space, where it flows round the brainstem, up over the hemispheres and down round the spinal cord.
It is absorbed mainly through the arachnoid granulations, tufts of arachnoid that push into the venous sinuses, such as the superior sagittal sinus, and act as one-way valves: CSF passes into the blood when its pressure exceeds that in the sinus. Some also drains along the sheaths of cranial and spinal nerves towards lymphatics. Absorption rises with pressure, so in health production and absorption balance at a normal pressure.
Underlying change · Step 1 of 5
Obstructive hydrocephalus: a block inside the ventricles
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Communicating hydrocephalus: CSF is not absorbed
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 5
Infants and adults: whether the skull can give way
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
Normal-pressure hydrocephalus in older adults
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
The look-alike: large ventricles from lost brain
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .