Hydrocephalus

Introduction

• Any condition where ventricles are enlarged
• Communicating hydrocephalus – extra ventricular obstruction
• Noncommunicating hydrocephalus – intra ventricular obstruction
• Ventriculomegaly – lack of brain parenchyma (atrophy or lack of development)
• Surgical intervention – role in cases where there is imbalance in CSF production and absorption 
• CSF formed by choroid plexus and drained mostly by brain and spinal cord, to lesser extent by arachnoid granulations
• Net CSF flow in direction of third to fourth ventricle, influenced by cerebrovascular pulsations

Neonates and infants

• Post hemorrhagic and post infectious, aqueduct stenosis, gliosis, Chiari II, Dandy-Walker malformation, vein of Galen malformation
• Progressive macrocephaly
• Frontal bossing
• Calvarial thinning 
• Tense, bulging anterior fontanelle
• Sutural diastases
• Enlarged scalp veins
• Sunsetting eyes with failure of upward gaze
• Lateral rectus palsy
• Leg spasticity (due to stretching of corticospinal tracts)

Older children

• Posterior fossa neoplasms, aqueduct stenosis
• Early morning headache
• Nausea, vomiting
• Papilledema
• Leg spasticity
• Cranial palsies
• Altered consciousness

Intra ventricular obstruction

• Temporal horns dilated disproportionate to lateral ventricular dilatation
• Enlarged anterior and posterior recesses of third ventricle
• Inferior convexity of floor of third ventricle
• Transependymal edema 
• Bulging of fontanelles
• Sulcal spaces, major fissures and basal cisterns small or obliterated
• Widening of radius of frontal horn with decrease in its angle with midline plane
• Erosion of dorsum sella
• Copper-beaten skull

Extra ventricular obstruction

• Could be totally normal in imaging 
• Mild sulcal or ventricular prominence
• Hemorrhage and protein debris in infection and malignancy
• Impaired venous drainage and venous hypertension
• Diffuse arteriopathies

The 0-2 years conundrum

• Variable rates of growth of skull and the developing brain can mimic hydrocephalus in the first 2 years of brain development
• Documentation of serial growth of head circumference and serial change in size of ventricles will offer more confidence in diagnosing hydrocephalus

11 – 20 years 

• It is normal for the scans to reveal thin ventricles and tight sulci in this age. It is perfectly normal and should not be misinterpreted as cerebral edema
• The basal cisterns will be of normal dimensions in all normal patients

Mechanical obstruction

• Narrowest parts of the ventricular system prone for mechanical obstruction
• Foramina of Monro
• Cerebral aqueduct
• Fourth ventricular outflow foramina

Foramina of Monro

• Superior extension of suprasellar tumors, arachnoid cysts, colloid cysts
• Giant cell astrocytoma in tuberous sclerosis

Cerebral aqueduct

• Tectal plate gliomas
• Superior extension of midline posterior fossa tumors, brain stem astrocytomas
• Inferior extension of pineal region tumors 
• Basal cisterns can get obstructed by diverticula arising from atria of dilated lateral ventricles. Distinguish this from arachnoid cysts by demonstrating continuity of these diverticula with the ventricular system

Pockets of CSF isolation

• Hemorrhage 
  • Hemosiderin staining, superficial siderosis, focal atrophy, porencephaly
• Infection
• Disseminated tumor 
• Reparative fibrosis
• Infections and tumors show hyperdense exudates in basal cisterns, subarachnoid space and pial enhancement 

Aqueduct stenosis

• Most common cause in children
• Present anytime from birth to adulthood
• Developmental or acquired
• Often due to infection or intraventricular hemorrhage
• Dilated lateral and third ventricles
• Normal fourth ventricle
• No tectal plate tumor
• Site of narrowing – proximal at level of superior colliculi in intercollicular sulcus
• Congenital webs are seen in distal aqueduct

CSF overproduction

• Choroid plexus papilloma
• Apart from excess production, these tumors exert mass effect at trigone of lateral ventricle or the foramen of Monro, also induce hemorrhage within the ventricle 

Spinal cord screening 

• Recommended in all cases of extra ventricular obstruction to rule out spinal cord neoplasms

Chiari II malformation 

• Presents early in life
• Craniocervical junction obstruction
• Displaced fourth ventricular outlet foramina adds to obstruction
• Poor CSF absorption capability of spinal cord

Shunt malfunction

• Occpital headaches at night
• Fourth ventricle is no longer slit like. Looks normal or dilated

Raised intracranial venous pressure

• Jugular outflow obstruction in craniosynostoses
• Venous thrombosis
• Vein of Galen aneurysm
• Dural arteriovenous shunts

CSF drainage techniques

• External ventricular drainage
• Ventriculoperitoneal shunt
• Ventriculoatrial shunt
• Third ventriculostomy

Shunt infection

• 1-5% incidence
• Higher in infants
• Signs of ventriculitis: hyper dense ependyma on CT, ependymal enhancement, debris in ventricles. Can also lead to cerebrates

Other shunt complications 

• Abdominal ascites
• Pseudocyst formation
• Perforated abdominal viscus

Slit ventricle syndrome

• Over drainage of CSF
• Stiff, poorly compliant ventricles