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PE27.4 | Hydrocephalus — SDL Guide

Learning Objectives

• Identify the clinical features of hydrocephalus in infants and older children, including the sunset sign
• Classify hydrocephalus as communicating or obstructive and explain the pathophysiological basis of each
• List the major causes of hydrocephalus in the paediatric age group
• Interpret OFC measurement, head CT/MRI findings, and cranial ultrasound in the diagnosis of hydrocephalus
• Outline the management options including VP shunt and endoscopic third ventriculostomy, and their complications

INSTRUCTIONS

Hydrocephalus — literally 'water on the brain' — is an abnormal accumulation of CSF within the ventricular system, leading to raised intracranial pressure and, if untreated, progressive brain damage. In India, it remains one of the most common paediatric neurosurgical conditions, occurring as a complication of meningitis, prematurity with intraventricular haemorrhage, congenital malformations, and neural tube defects. The clinical picture in infants is distinct from older children because of the open fontanelle and unfused sutures — knowing these age-specific presentations allows you to recognise hydrocephalus before irreversible neurological damage occurs.

References

• Ghai Essential Pediatrics, 9th ed., Ch 18 (Neurological Conditions) (textbook)
• Nelson Textbook of Pediatrics, 21st ed., Ch 610 (Hydrocephalus) (textbook)
• IAP Guidelines on Paediatric Neurosurgical Conditions (guideline)

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Version 2.0 | NMC CBUC 2024

Clinical Presentation of Hydrocephalus

The clinical presentation of hydrocephalus is dramatically age-dependent, and understanding this age-dependence is the key to not missing the diagnosis in clinical practice. The fundamental variable is the degree of fontanelle and cranial suture patency — a property that changes continuously through the first two years of life. In young infants, the fontanelle is open and the cranial sutures are unfused, so the expanding skull can accommodate slowly rising CSF pressure by growing outward. The result is that raised ICP in infants is signalled primarily by an enlarging head circumference and bulging fontanelle rather than by the headache and vomiting that dominate the picture in older children. In older children beyond 18–24 months, the sutures are fused and the skull is rigid; raised ICP cannot be absorbed by calvarial expansion and instead produces the classic acute-onset raised-ICP syndrome of headache, vomiting, and papilloedema. This age-based difference in skull compliance means that the same degree of ventricular dilation will produce very different clinical pictures depending on the child's age — a principle that fundamentally organises your approach to examination and interpretation.

In infants (fontanelle open, sutures unfused):
• Macrocephaly: The most consistent and measurable sign. Occipito-frontal circumference (OFC) exceeds the 98th centile (>2 SD above the mean) for age and sex, OR is crossing centile lines on serial measurements at an abnormal velocity. A single above-normal measurement may reflect familial macrocephaly; an accelerating OFC that crosses two or more centile lines is a red flag requiring investigation.
• Bulging anterior fontanelle: Tense or bulging even when the infant is upright and not crying — indicates raised ICP transmitted through the patent fontanelle.
• Dilated scalp veins: CSF pressure impairs venous drainage from the scalp, distending the visible scalp veins in a characteristic fan-like pattern.
• Sunset sign (Parinaud's sign variant): Tonic downward deviation of both eyes, with the sclerae visible above the iris — the classic 'setting sun' appearance. Caused by pressure on the midbrain pretectal area (Edinger-Westphal nucleus-region) impairing upgaze. This is a specific and important sign of raised ICP in infants. Note: it is NOT a physiological sign in healthy infants beyond the neonatal period.
• Prominent forehead (frontal bossing): Result of the disproportionate anterior expansion of the calvarium.
• Craniotabes: Eggshell-like cracking of the thinned skull on pressure over the parieto-occipital region (Macewen's sign).
• Developmental delay (motor milestones first, as periventricular motor tracts are compressed), poor feeding, irritability.

In older children (sutures fused):
The skull cannot expand, so raised ICP manifests acutely:
• Headache: Typically worst in the morning (recumbent position increases ICP at night), improved by sitting up. Morning vomiting without nausea (projectile) is characteristic.
• Papilloedema on fundoscopy: venous pulsations absent, blurred disc margin, disc elevation — indicates chronic raised ICP; rarely present in acute hydrocephalus.
• Cushing's triad: Bradycardia, systolic hypertension, and irregular respirations — indicates imminent herniation; a late and ominous sign.
• Sixth nerve palsy (CN VI) — a false localising sign from raised ICP stretching the nerve over the petrous bone.

Infant Hydrocephalus: Clinical Signs and CSF Pathophysiology

Pathophysiology and Classification of Hydrocephalus

The normal CSF cycle is a continuous loop: production at the choroid plexus (primarily in the lateral ventricles) → flow through the foramina of Monro into the third ventricle → through the cerebral aqueduct (aqueduct of Sylvius) into the fourth ventricle → out through the foramina of Magendie and Luschka into the subarachnoid space → absorption at the arachnoid granulations along the sagittal sinus. Hydrocephalus results whenever this loop is disrupted: either by obstruction of CSF flow within the ventricular system, or by failure of CSF resorption at the arachnoid granulations, or rarely by excess CSF production (choroid plexus papilloma).

Provided image

The clinical classification that matters most for management is the distinction between communicating (non-obstructive) and obstructive (non-communicating) hydrocephalus, because it determines the surgical approach.

Communicating hydrocephalus:
All CSF pathways remain open (communication between ventricles and subarachnoid space is intact), but resorption at the arachnoid granulations is impaired. The commonest paediatric cause is post-meningitis fibrosis — both bacterial and tuberculous meningitis cause a fibrotic reaction in the basal cisterns and over the arachnoid granulations, permanently impairing their resorptive capacity. Other causes include post-haemorrhagic (post-IVH in premature infants), subarachnoid haemorrhage, and choroid plexus papilloma (excess production).

Obstructive (non-communicating) hydrocephalus:
CSF flow is blocked at some point within the ventricular system, before reaching the subarachnoid space. The blocked segment determines which ventricles dilate:
• Aqueductal stenosis — most common cause of congenital obstructive hydrocephalus; narrowing or obstruction of the aqueduct of Sylvius → dilation of lateral and third ventricles but normal fourth ventricle; may be isolated or associated with X-linked inheritance (L1CAM gene mutation)
• Dandy-Walker malformation — cystic dilation of the fourth ventricle with hypoplasia of the cerebellar vermis; all four ventricles can dilate
• Posterior fossa tumour or cyst — compresses the fourth ventricle or aqueduct
• Intraventricular haemorrhage (preterm neonates) — blood clot obstructs the aqueduct or foramina
• Neural tube defects (meningomyelocele with Arnold-Chiari II malformation) — hindbrain herniation into the cervical canal obstructs CSF outflow

Hydrocephalus ex vacuo (IMPORTANT misnomer):
Ventricular enlargement caused by loss of brain parenchyma (atrophy) — NOT true hydrocephalus. There is no raised ICP. Seen in severe cerebral atrophy (hypoxic-ischaemic encephalopathy, advanced metabolic disease). CT shows large ventricles and widened sulci. Management: treat the underlying cause; NO shunting required.

Diagnosis and Investigation

The diagnosis of hydrocephalus begins with a simple clinical measurement — the occipito-frontal circumference (OFC) — and is confirmed by neuroimaging. In infants, this is a primarily clinical-radiological diagnosis; in older children, the presentation with raised ICP symptoms makes neuroimaging urgent.

Occipito-frontal circumference (OFC) measurement:
Measure with a non-stretchable tape around the largest circumference of the head (over the most prominent part of the occiput and the most prominent part of the forehead). Plot on a gender-specific WHO/IAP growth chart. A single measurement above the 98th centile (>2 SD) requires plotting to assess trajectory; serial measurements crossing 2+ centile lines upward within weeks are abnormal and indicate rapidly progressive hydrocephalus. Familial macrocephaly (measure parental OFC — typically large in both parents) must be distinguished from pathological expansion.

Cranial ultrasonography (neonates and infants):
Through the open anterior fontanelle, cranial USG provides a radiation-free, bedside assessment of ventricular size and architecture. Measurements: the ventricular index (Levene's chart) and the anterior horn width are compared against gestational-age-specific norms. USG is the first-line investigation for suspected hydrocephalus in neonates and infants due to its safety and availability in NICUs and peripheral hospitals. It allows serial monitoring without radiation exposure.

CT brain (with contrast for suspected mass lesion):
CT provides rapid cross-sectional imaging of ventricular size, identifies the likely site of obstruction (aqueduct stenosis vs fourth ventricular outlet), and detects associated pathology (posterior fossa tumour, haemorrhage, tuberculomata). Ventriculomegaly — dilatation of the ventricular system on CT — is graded by the ratio of the frontal horn width to the internal skull diameter (FHW/ISD > 0.33 is abnormal). Periventricular lucency (transependymal CSF seepage) on CT indicates active raised ICP.

MRI brain:
MRI provides superior soft-tissue detail: aqueduct flow studies (phase-contrast MRI demonstrates CSF flow through the aqueduct — absent in aqueductal stenosis), posterior fossa anatomy (Dandy-Walker, Chiari malformations), and detection of white matter changes. MRI is the preferred imaging modality for planning surgical intervention, particularly endoscopic third ventriculostomy.