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 1, 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 1

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. 9