What is hydrocephalus?

What is Hydrocephalus

Hydrocephalus is an excessive accumulation of cerebrospinal fluid (CSF) in the brain that increases intracranial pressure and damages brain tissue. 1

Core Pathophysiology

The condition results from impaired CSF homeostasis, leading to active expansion of the cerebral ventricles. 2 The mechanisms involve:

• Impaired CSF absorption at the arachnoid granulations due to fibrosis, meningeal scarring, and subependymal gliosis 3
• Obstruction of CSF flow pathways through the ventricular system 1
• Dysfunctional cerebral pulsations and altered brain compliance 4
• Disrupted water-transport mechanisms at the CSF-brain interface 2

Normal CSF production occurs at the choroid plexus in the lateral ventricles, flowing through the third and fourth ventricles to the subarachnoid space where it is absorbed. 5 When this circulation is disrupted, ventricular expansion occurs. 2

Clinical Impact on Morbidity and Mortality

Uncontrolled hydrocephalus leads to macrocephaly, developmental delays, and neurological deficiencies that significantly affect quality of life and survival. 1 The severity of neurological deficiencies and longevity depend on the underlying etiology. 1

Age-Specific Presentations

In infants, the most common presentations include 6:

• Progressive head circumference increase (macrocephaly)
• Bulging fontanelle that is tense and non-pulsatile
• Splaying of cranial sutures
• "Sunset eyes" (downward eye deviation with visible sclera above iris)
• Irritability and lethargy

In older children and adults, typical symptoms include 6:

• Headache (often worse when upright, relieved by lying down)
• Nausea and vomiting
• Altered mental status (confusion to lethargy)
• Visual disturbances (diplopia, blurred vision, visual field defects)
• Gait abnormalities

Classification Systems

By Communication Status

Communicating hydrocephalus occurs when CSF pathways remain patent but absorption is impaired, primarily at the arachnoid granulations. 3 The ventricular system communicates with the subarachnoid space. 5

Non-communicating (obstructive) hydrocephalus results from blockage within the ventricular system itself, preventing CSF flow between ventricles. 5

By Timing of Onset

Congenital hydrocephalus is present at or near birth and has been linked to gene mutations that disrupt brain morphogenesis. 2 Common causes include aqueductal stenosis, myelomeningocele (spina bifida affects 80% of children), and posterior fossa malformations. 7, 8

Acquired hydrocephalus develops after birth from central nervous system infection, hemorrhage, or tumors, with inflammation-dependent dysregulation of CSF secretion and clearance. 2

Major Etiologic Categories

Post-Infectious Causes

• Meningitis is a leading cause, particularly in lower-middle-income countries where it accounts for 19.2% of pediatric cases 3
• Coccidioidal meningitis causes hydrocephalus in approximately 40% of affected individuals 9, 3
• Geographic variation exists, with postinfectious hydrocephalus most common in South Asia (23.2%) 1

Post-Hemorrhagic Causes

• Intraventricular hemorrhage in premature infants affects 15-20% of infants weighing less than 1500g at birth 7
• Subarachnoid hemorrhage damages CSF absorption sites 3

Neoplastic Causes

• Brain tumors, particularly fourth ventricular tumors (medulloblastoma, ependymoma) and posterior fossa masses 7
• Leptomeningeal metastases obstruct CSF flow in the subarachnoid space 3

Spinal Dysraphism

• Myelomeningocele causes hydrocephalus in approximately 80% of affected children through Chiari II malformation and aqueductal compression 7

Critical Clinical Distinctions

Warning Signs Requiring Urgent Evaluation

Acute obstructive hydrocephalus presents with rapid onset (hours to days) and includes 6, 7:

• Sudden severe headache ("worst headache of life")
• Rapid deterioration in mental status
• Papilledema
• Parinaud's syndrome (cranial nerve palsies affecting eye movements)
• Bradycardia with hypertension (indicating critical ICP elevation)

In infants, emergency signs include 6:

• Apnea and bradycardia episodes
• Respiratory irregularities

Common Diagnostic Pitfalls

Symptoms may be subtle, especially in young and middle-aged adults, with discrepancy between prominent symptoms and subtle clinical signs. 6 Postural headache may be confused with spontaneous intracranial hypotension. 6

Treatment Principles

Early diagnosis and surgical treatment are current mainstays for reducing morbidity and mortality from hydrocephalus. 1, 6 Treatment options include:

• CSF shunting (ventriculoperitoneal or other shunt types) 5
• Endoscopic third ventriculostomy (ETV) with or without choroid plexus cauterization 2, 5
• Ventricular drainage for acute hydrocephalus, particularly when associated with decreased level of consciousness 10

For communicating hydrocephalus, serial lumbar punctures can be therapeutic if the lumbar subarachnoid space communicates with the ventricular system. 3 Medical management with acetazolamide and furosemide has limited benefit and most patients still require surgery. 11