Medicine chapters
Hydrocephalus and idiopathic intracranial hypertension
How CSF builds up in the head, the difference between obstructive and communicating hydrocephalus, normal pressure hydrocephalus, and idiopathic intracranial hypertension in young overweight women.
- Hydrocephalus is too much CSF in the ventricles from a block to flow (obstructive) or poor absorption (communicating); LP is dangerous in the obstructive type.
- Normal pressure hydrocephalus in the elderly gives the triad gait apraxia, dementia, urinary incontinence and may improve with a shunt.
- IIH is raised CSF pressure with papilloedema and normal imaging, typically in young overweight women; treat with weight loss and acetazolamide and protect vision.
On this page
Overview
Hydrocephalus means an excess of cerebrospinal fluid (CSF) inside the head, with enlarged ventricles. It happens when CSF is made in excess, cannot flow, or is not absorbed.
Idiopathic intracranial hypertension (IIH) is the opposite picture on a scan: CSF pressure is high, but the ventricles are normal or small and there is no mass.
Both conditions threaten life or sight, and both are common MCQ topics because of their classic triads and "who gets it" stems.
CSF physiology in brief
- CSF is made mainly by the choroid plexus in the ventricles. Total volume is about 150 mL, and about 20 mL is produced each hour.
- Route: lateral ventricles → foramen of Monro → third ventricle → aqueduct of Sylvius → fourth ventricle → foramina of Magendie (midline) and Luschka (lateral) → subarachnoid space.
- Absorption: through the arachnoid villi (granulations) into the superior sagittal sinus.
"Monro to three, Sylvius to four, Magendie in the middle, Luschka at the side door."
Types of hydrocephalus
| Type | Where the problem is | Ventricles on CT | Typical causes |
|---|---|---|---|
| Obstructive (non-communicating) | Block inside the ventricular system or its exit foramina | Dilated above the block only | Aqueduct stenosis, posterior fossa tumour, colloid cyst of the third ventricle, Dandy–Walker, Arnold–Chiari |
| Communicating | Flow out of the ventricles is open, but absorption at the arachnoid villi fails | All four ventricles dilated | After meningitis (especially tuberculous), after subarachnoid haemorrhage or head injury, high CSF protein |
| Over-production (rare) | Too much CSF made | All dilated | Choroid plexus papilloma |
Reading the CT: dilated lateral ventricles with a normal fourth ventricle points to a block at the aqueduct; dilated lateral ventricles with a normal third ventricle points to a block at the foramen of Monro (for example a colloid cyst).
Lumbar puncture is dangerous in obstructive hydrocephalus (and any mass lesion), because draining CSF from below can make the brainstem and cerebellar tonsils herniate ("coning"). In communicating hydrocephalus, LP is both diagnostic and can relieve pressure for a while.
Causes in infants and children
- Aqueduct stenosis: congenital (including an X-linked form, sometimes with flexed adducted thumbs) or acquired after neonatal meningitis or haemorrhage. It is the commonest cause of congenital obstructive hydrocephalus.
- Arnold–Chiari malformation: the cerebellar tonsils sit low in the cervical canal; often with spina bifida (myelomeningocele); syringomyelia may follow.
- Dandy–Walker malformation: small cerebellar vermis with a large cystic fourth ventricle and blocked outlet foramina.
- Intraventricular haemorrhage in preterm babies and neonatal meningitis.
- Congenital infections such as toxoplasmosis (hydrocephalus, scattered intracranial calcification and chorioretinitis).
Causes in adults
- Posterior fossa and brainstem tumours blocking the aqueduct or fourth ventricle.
- Subarachnoid haemorrhage, head injury, meningitis (tuberculous meningitis is an important cause in Pakistan).
- Colloid cyst of the third ventricle: intermittent blockage at the foramen of Monro, giving sudden severe headaches, sometimes with leg weakness or drop attacks, often brought on by head position.
- Choroid plexus papilloma (rare) making excess CSF.
- Often no cause is found. Childhood hydrocephalus that had stabilised ("arrested") can decompensate later in life.
Clinical features
Infants (skull sutures still open)
- Head circumference rising faster than normal, crossing centile lines.
- Tense, bulging anterior fontanelle, widened sutures, prominent scalp veins.
- "Sunsetting" eyes: loss of upgaze from pressure on the dorsal midbrain (Parinaud syndrome).
- Vomiting, irritability, poor feeding, then drowsiness.
Older children and adults (rigid skull)
- Features of raised ICP: headache worse on lying, coughing or bending, vomiting, blurred or double vision.
- Papilloedema; VIth nerve palsy as a false localising sign.
- Drowsiness, then coma. Acute obstructive hydrocephalus can deteriorate very fast.
- Elderly patients may show only slowly worsening gait, memory and bladder control.
Investigations
- CT head: first-line; shows ventricular size, level of the block, and any mass.
- MRI: better for the posterior fossa, aqueduct, Chiari malformation and planning endoscopic surgery.
- Ultrasound through the fontanelle in infants.
- LP with opening pressure: only after imaging has excluded a mass or obstructive pattern.
Management of hydrocephalus
- Treat the cause where possible, for example remove a tumour or colloid cyst.
- External ventricular drain (EVD): emergency, temporary drainage in a drowsy or deteriorating patient.
- Ventriculoperitoneal (VP) shunt: catheter from a lateral ventricle, through a valve, tunnelled under the skin to the peritoneum. Ventriculoatrial and lumboperitoneal routes also exist.
- Endoscopic third ventriculostomy (ETV): a hole is made in the floor of the third ventricle so CSF bypasses a block. Best for aqueduct stenosis; avoids an implanted tube.
Shunt complications
| Problem | Clues |
|---|---|
| Blockage | Return of raised ICP symptoms; a common reason for revision |
| Infection | Most appear within the first month after insertion; usually skin organisms; shunt is removed and CSF drained during antibiotics |
| Over-drainage | Headache worse on standing; subdural hygroma or haematoma; slit ventricle syndrome in children |
| Abdominal | CSF pseudocyst around the peritoneal tip, abdominal distension |
Normal pressure hydrocephalus (NPH)
- Seen in elderly people. The lateral ventricles are enlarged, and the pressure is normal on a single LP but probably rises intermittently, so the name is misleading.
- May follow subarachnoid haemorrhage, meningitis or head injury, or arise with no cause.
- Classic triad:
1. Gait disturbance: broad-based, shuffling, "magnetic" or apraxic gait (usually the first and most responsive feature). 2. Dementia: slowed thinking, poor attention. 3. Urinary incontinence.
- Diagnosis: imaging shows ventricles enlarged out of proportion to cortical atrophy. A large-volume LP (tap test) or several days of lumbar CSF drainage that improves the gait predicts benefit from a shunt.
- Treatment: VP shunt.
NPH = "wet, wobbly and wacky": incontinence, gait apraxia and dementia.
NPH is one of the few reversible causes of dementia, so it should be looked for in any elderly patient with a gait problem plus memory loss.
Idiopathic intracranial hypertension (IIH)
Older names: benign intracranial hypertension and pseudotumour cerebri. "Benign" is misleading, because untreated cases can go blind.
Who gets it
- Typically young, overweight women of child-bearing age; many have polycystic ovaries.
- Probably due to reduced CSF absorption; raised venous or intra-abdominal pressure in obesity may play a part.
Associated drugs and conditions
- Tetracyclines (for example minocycline or doxycycline for acne).
- Vitamin A excess and retinoids.
- Combined oral contraceptive pill, corticosteroid withdrawal, growth hormone treatment.
Clinical features
- Headache, often daily and worse lying down or in the morning.
- Transient visual obscurations: seconds of greying or blacking out of vision, often on standing or bending.
- Pulsatile tinnitus.
- Papilloedema, usually bilateral and florid, with an enlarged blind spot.
- VIth nerve palsy (false localising sign), giving horizontal double vision.
- The patient is alert with no focal signs apart from the VIth nerve.
Investigations (the diagnosis is one of exclusion)
| Test | Finding in IIH |
|---|---|
| MRI brain | Normal; ventricles normal or slit-like; no mass or hydrocephalus |
| MR venography | Normal; done to exclude cerebral venous sinus thrombosis, which can look identical |
| LP | Raised opening pressure (above about 25 cm of CSF), with normal CSF contents (cells, protein, glucose) |
| Perimetry (visual fields) | Enlarged blind spot, then peripheral field loss; used to monitor |
A young woman on the pill with headache, papilloedema and drowsiness or seizures may have venous sinus thrombosis, not IIH. IIH patients are alert and have normal imaging, including venography.
Management
- Weight loss: helpful and often the most important long-term step.
- Stop any causative drug.
- Acetazolamide (carbonic anhydrase inhibitor): first-line drug; reduces CSF production by the choroid plexus. Side effects: tingling, taste change, kidney stones, metabolic acidosis.
- Thiazide diuretics are an alternative; repeated LP gives short-term relief.
- Surgery to save sight if vision worsens despite medical treatment: optic nerve sheath fenestration, or a lumboperitoneal or VP shunt.
- Regular visual field checks are essential; headache can improve while vision is silently lost.
In IIH the thing to protect is vision. Progressive field loss on perimetry is the indication for urgent surgery.
Expect: the normal CSF pathway and where it is absorbed; obstructive versus communicating hydrocephalus and why LP is dangerous in the obstructive type; aqueduct stenosis as the commonest congenital cause; tuberculous meningitis causing communicating hydrocephalus; infant signs such as bulging fontanelle and sunsetting eyes; the NPH triad and its treatment by shunt; the typical IIH patient (young obese woman), drug causes such as tetracyclines and vitamin A, normal imaging with raised opening pressure and normal CSF, the VIth nerve palsy, acetazolamide as first-line treatment, and the need to exclude venous sinus thrombosis.
Quick revision
- CSF: choroid plexus → Monro → third → aqueduct → fourth → Magendie/Luschka → arachnoid villi → superior sagittal sinus.
- Obstructive: block within ventricles; LP contraindicated. Communicating: absorption fails (post-meningitis, post-SAH).
- Commonest congenital cause: aqueduct stenosis. Colloid cyst blocks the foramen of Monro.
- Infant: big head, bulging fontanelle, sunsetting eyes.
- Treatment: VP shunt; ETV for aqueduct stenosis; EVD in emergencies.
- NPH: gait apraxia + dementia + incontinence; shunt may help.
- IIH: young obese woman, headache, papilloedema, VIth nerve palsy, normal MRI and MRV, high opening pressure, normal CSF.
- IIH treatment: weight loss, acetazolamide, stop culprit drug, fenestration or shunt to save sight.
Written by The House Job from standard references (Kumar and Clark's Clinical Medicine; Bailey and Love's Short Practice of Surgery).
FAQ
What is the difference between obstructive and communicating hydrocephalus?
In obstructive hydrocephalus CSF cannot get out of the ventricular system, so only the ventricles above the block enlarge; in communicating hydrocephalus CSF leaves the ventricles but is not absorbed, so all four ventricles enlarge.
Why is IIH called a diagnosis of exclusion?
Because a mass, hydrocephalus, venous sinus thrombosis and abnormal CSF must all be ruled out before raised pressure can be called idiopathic.
How does acetazolamide help in IIH?
It blocks carbonic anhydrase in the choroid plexus and so reduces the amount of CSF produced, lowering pressure.
Which feature of normal pressure hydrocephalus usually improves most after shunting?
The gait disturbance tends to respond best, while long-standing dementia improves less.