Paediatrics chapters
Hydrocephalus and microcephaly
Disorders of head size in children: how CSF is made and absorbed, obstructive and communicating hydrocephalus with their causes, signs and shunt treatment, and the causes and work-up of a small head.
- Hydrocephalus is excess CSF in the ventricles from blocked flow (obstructive: aqueductal stenosis, Chiari II, Dandy-Walker, tumours), poor absorption (communicating: after meningitis or haemorrhage) or rarely overproduction (choroid plexus papilloma).
- Infants show a rapidly enlarging head, bulging fontanelle, separated sutures, dilated scalp veins, sunset eyes and leg spasticity; older children show headache, vomiting and papilloedema; ultrasound, CT or MRI confirm, and a ventriculoperitoneal shunt is the main treatment.
- Microcephaly is a head circumference below the 3rd percentile (Akbar: over 3 SD below the mean), usually reflecting a small brain from genetic causes or prenatal or early brain injury (TORCH, asphyxia); craniosynostosis is a rare skull cause.
On this page
Overview
Head size reflects brain and ventricle size. A head that is too big or growing too fast may mean hydrocephalus; a head that is too small (microcephaly) usually means a small brain. Measuring the head circumference serially and plotting it on a chart is one of the most useful bedside tests in paediatrics; the rate of growth matters more than a single reading.
Normal head growth
- Average head circumference at birth is about 35 cm in boys and 34 cm in girls (Akbar).
- Growth is fastest early: about 2 cm per month in the first 3 months, slowing to about 0.5 cm per month from 6 to 12 months.
- The brain reaches about 25% of adult volume at birth and about 75% by 1 year.
CSF physiology
- CSF is formed mainly by the choroid plexus, mostly in the lateral ventricles; about a quarter comes from other sources.
- It flows: lateral ventricles → foramen of Monro → third ventricle → aqueduct of Sylvius → fourth ventricle → foramina of Magendie and Luschka → subarachnoid space and basal cisterns.
- It is absorbed through the arachnoid villi into the dural venous sinuses (superior sagittal sinus).
- Volume: about 50 ml in an infant and 150 ml in older children; production about 20 ml per hour, so it turns over 3-4 times a day.
Hydrocephalus
Definition
A congenital or acquired disorder with excess CSF inside the cerebral ventricles, which are dilated, usually with raised pressure.
Mechanisms and types
| Type | Problem | Ventricles | Examples |
|---|---|---|---|
| Non-communicating (obstructive) | Block inside the ventricular system; ventricles do not communicate with the subarachnoid space | Dilated above the block only | Aqueductal stenosis, Chiari II, Dandy-Walker, tumours (posterior fossa, pineal), abscess, haematoma, vein of Galen malformation, post-infective or post-haemorrhagic gliosis of the aqueduct |
| Communicating | Block outside the ventricles or failed absorption by the arachnoid villi | All ventricles dilated | After meningitis (pneumococcal, tuberculous), subarachnoid or intraventricular haemorrhage, intrauterine infection, meningeal leukaemia, achondroplasia, venous sinus thrombosis |
| Overproduction | Too much CSF | All dilated | Choroid plexus papilloma |
In aqueductal stenosis the lateral and third ventricles are dilated but the fourth ventricle is normal. In communicating hydrocephalus all four are enlarged.
Causes by timing
- Congenital: aqueductal stenosis; Arnold-Chiari type II (with myelomeningocele: cerebellar tonsils and medulla pushed down through the foramen magnum); Dandy-Walker malformation; arachnoid cysts; intrauterine infections (toxoplasmosis, CMV, rubella, syphilis); Klippel-Feil syndrome.
- Acquired: bacterial and tuberculous meningitis, intraventricular haemorrhage of prematurity, subarachnoid bleeding (aneurysm, AVM, trauma), brain tumours.
Dandy-Walker malformation
- Classic triad: absent or small cerebellar vermis, cystic dilatation of the fourth ventricle, and an enlarged posterior fossa.
- Infants: slow motor development, enlarging skull, bulging at the back of the head; older children: raised ICP and cerebellar signs (unsteadiness, jerky eye movements).
- Diagnosed on prenatal ultrasound; treat hydrocephalus with a shunt and support development.
Clinical features
Signs depend on the age and how fast the hydrocephalus develops.
| Infants (open sutures) | Older children (closed sutures) |
|---|---|
| Rapid increase in head circumference (the most prominent sign) | Headache, worse in the morning, with vomiting |
| Bulging, tense anterior fontanelle | Papilloedema |
| Separated sutures; Macewen (cracked-pot) sign on percussion | Sixth nerve palsy, squint, diplopia |
| Dilated scalp veins | Irritability, lethargy, behaviour change |
| Sunset sign: eyes deviated down with sclera visible above the iris (upward gaze palsy) | Changes in pulse, blood pressure and breathing |
| Spasticity of the legs more than arms, brisk reflexes, clonus, Babinski | Endocrine and visual problems with third ventricle dilatation |
| Irritability, poor feeding, vomiting, developmental delay |
- Leg fibres are stretched first because they run closest to the dilated lateral ventricles (hence early leg spasticity).
- Infants with an open fontanelle rarely develop papilloedema or a sixth nerve palsy (Nelson).
- The Cushing triad (high blood pressure, slow pulse, irregular breathing) is a late sign of critically raised pressure.
"Big head, Bulging fontanelle, Bright scalp veins, setting-sun eyes."
In infants the rate of head growth is the earliest and most useful sign; papilloedema is rare while the fontanelle is open.
A big head is not always hydrocephalus: thick skull (thalassaemia, rickets), subdural collections and familial macrocephaly are common causes.
Investigations
- Serial head circumference on a chart.
- Cranial ultrasound through the fontanelle in infants; CT or MRI show which ventricles are dilated, the cause and periventricular oedema. MRI is better for the posterior fossa.
- Skull X-ray (chronic raised pressure): separated sutures, eroded clinoids and increased convolutional markings (beaten-silver appearance).
- CSF only if recent infection or bleeding is suspected; lumbar puncture is contraindicated with a mass lesion or obstructive hydrocephalus.
Differential diagnosis of a large head
| Group | Examples |
|---|---|
| Thick skull (macrocrania) | Thalassaemia and chronic anaemia, rickets, osteogenesis imperfecta, achondroplasia, osteopetrosis |
| Big ventricles | Hydrocephalus |
| Fluid or mass | Subdural effusion or haematoma, cysts, tumour |
| Big brain (megalencephaly) | Neurofibromatosis, tuberous sclerosis, Sotos syndrome, storage disorders (Canavan, Alexander, mucopolysaccharidoses) |
| Benign | Familial macrocephaly (measure the parents), benign extracerebral collections |
Nelson defines macrocephaly as a head circumference above the 97th percentile; most often it is a harmless family trait.
Management
- Treat the cause (meningitis, tumour, abscess).
- Ventriculoperitoneal (VP) shunt: the most effective treatment for progressive hydrocephalus; tubing from a lateral ventricle to the peritoneal cavity.
- Shunt complications: blockage (signs of acute raised ICP return) and infection, usually Staphylococcus epidermidis, causing ventriculitis or meningitis.
- Medical treatment to reduce CSF production in slowly progressive or temporary hydrocephalus (after meningitis or haemorrhage): acetazolamide, furosemide.
A child with a VP shunt who develops headache, vomiting, drowsiness or fever has shunt blockage or infection until proved otherwise.
Prognosis
- Depends on the cause (intrauterine infection, meningitis and tumour do worse) and how fast it is treated.
- Main disabilities: motor problems (spasticity, poor coordination), visual loss (optic atrophy from long-standing pressure) and intellectual impairment.
- White matter is hit harder than grey matter, so intellect is usually less affected than motor function.
Microcephaly
Definition
- A head circumference below the 3rd percentile for age and sex (Nelson); Akbar uses more than 3 SD below the mean.
- A small skull usually means a small brain (micrencephaly); rarely the skull itself fails to grow because sutures fuse early (craniosynostosis), which is recognised by an abnormal head shape.
- The smaller the head, the less likely intelligence is normal (Akbar: intellectual disability in about a third at 2-3 SD below the mean and in nearly two thirds beyond 3 SD). Exceptions include familial small heads.
Causes
| Primary (genetic or developmental) | Secondary (acquired) |
|---|---|
| Familial (autosomal recessive or dominant) | Congenital infections: CMV, rubella, toxoplasmosis, syphilis, varicella, HIV |
| Chromosomal: trisomy 21, 13, 18, cri-du-chat (5p deletion), Angelman, Prader-Willi | Hypoxic-ischaemic encephalopathy, periventricular leukomalacia |
| Brain malformations: holoprosencephaly, lissencephaly, schizencephaly, polymicrogyria, encephalocele, agenesis of the corpus callosum | Meningitis, encephalitis, stroke |
| Syndromes: Cornelia de Lange, Smith-Lemli-Opitz, Rubinstein-Taybi, Seckel | Toxins: fetal alcohol syndrome, maternal phenylketonuria, fetal radiation |
| Maternal diabetes, malnutrition, chronic heart, lung or kidney disease |
- Microcephaly present at birth is usually genetic or intrauterine; microcephaly appearing after birth (normal at birth, then poor head growth) suggests postnatal brain injury.
- Insults after 2 years rarely cause severe microcephaly, because most brain growth is complete.
Evaluation
- History: family head sizes, consanguinity, pregnancy exposures (infection, alcohol, drugs, radiation, maternal PKU or diabetes), birth asphyxia, early fever or seizures, development.
- Examination: serial head size, dysmorphic features, sloping forehead and small fontanelle, and TORCH signs (petechiae, hepatosplenomegaly, chorioretinitis, intracranial calcification). In a term baby, a chest circumference larger than the head suggests microcephaly.
- Tests: CT or MRI (malformations, atrophy, calcification, craniosynostosis), karyotype, TORCH serology and urine CMV culture, amino and organic acids, ammonia, maternal phenylalanine.
CMV is a classic cause of microcephaly with periventricular calcification; toxoplasmosis more often causes hydrocephalus with scattered calcification.
Management and prognosis
- No cure; treat seizures, physiotherapy, nutrition, special education, genetic counselling.
- Outcome depends on the cause; children whose microcephaly is part of a malformation syndrome or congenital infection do poorly.
- Some cases are preventable: avoiding birth asphyxia, early treatment of PKU and hypothyroidism.
Expect: CSF pathway and absorption; obstructive versus communicating hydrocephalus with examples; aqueductal stenosis sparing the fourth ventricle; Chiari II with myelomeningocele; Dandy-Walker triad; infant signs (rapid head growth, bulging fontanelle, sunset sign, Macewen sign, leg spasticity); VP shunt and its blockage and Staph. epidermidis infection; acetazolamide; causes of a big head (thalassaemia, rickets, familial); microcephaly definition and causes (TORCH, especially CMV with calcification, fetal alcohol, maternal PKU, chromosomal); craniosynostosis.
Quick revision
- CSF: choroid plexus, Monro, third ventricle, aqueduct, fourth ventricle, Magendie and Luschka, arachnoid villi.
- Obstructive: aqueductal stenosis, Chiari II, Dandy-Walker, tumour; communicating: after meningitis or bleeding.
- Aqueductal stenosis: lateral and third dilated, fourth normal.
- Infants: fast head growth, bulging fontanelle, sunset eyes, scalp veins, leg spasticity.
- VP shunt; blockage and Staph. epidermidis infection; acetazolamide for temporary cases.
- Macrocephaly over 97th centile; often familial.
- Microcephaly under 3rd centile; small brain; TORCH, HIE, chromosomal, alcohol, maternal PKU.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).
FAQ
What is the difference between obstructive and communicating hydrocephalus?
In obstructive hydrocephalus CSF is blocked within the ventricles, so only the ventricles above the block enlarge. In communicating hydrocephalus the block is outside the ventricles or absorption fails, so all ventricles enlarge.
Why do children with hydrocephalus have stiff legs?
The leg fibres of the corticospinal tracts run closest to the lateral ventricles, so they are stretched first as the ventricles enlarge.
What should you suspect when a child with a shunt becomes unwell?
Shunt blockage or shunt infection. Headache, vomiting, drowsiness, a bulging fontanelle or fever need urgent assessment.
Does a small head always mean intellectual disability?
No. Familial small heads can have normal intelligence, but the smaller the head, the higher the chance of intellectual disability, especially when it is due to a malformation or congenital infection.