Causes of Obstructive Hydrocephalus
Obstructive (non-communicating) hydrocephalus results from physical blockage of cerebrospinal fluid (CSF) pathways within the ventricular system, most commonly at the aqueduct of Sylvius, fourth ventricular outlets, or third ventricle.
Pediatric Population
Congenital Causes
Aqueductal stenosis is a leading congenital cause of obstructive hydrocephalus, presenting either at birth or later in childhood when compensatory mechanisms fail 1. This can be:
- Primary congenital stenosis from developmental abnormalities affecting brain morphogenesis 2
- Genetic mutations that disrupt the biomechanics of the CSF-brain interface 2
- Aqueductal webs, which are rare membranous obstructions that can present even in adolescence with headaches and vomiting 1
Spina bifida (myelomeningocele) causes obstructive hydrocephalus in approximately 80% of affected children, making it one of the most common congenital causes globally 3. The mechanism involves:
- Chiari II malformation with posterior fossa crowding
- Obstruction at the fourth ventricular outlets
- Aqueductal compression 3
Other structural malformations include:
- Dandy-Walker malformation with fourth ventricular outlet obstruction 4
- Posterior fossa cysts causing mass effect 4
Acquired Causes in Pediatrics
Brain tumors are a major cause of acquired obstructive hydrocephalus, particularly:
- Fourth ventricular tumors (medulloblastoma, ependymoma) causing outlet obstruction 5
- Posterior fossa masses compressing the aqueduct 5
- Pineal region tumors obstructing the aqueduct 4
- These are frequently diagnosed late in low- and middle-income countries, increasing morbidity 5
Post-infectious hydrocephalus can cause obstruction through:
- Aqueductal stenosis secondary to ventriculitis, where inflammation causes scarring and narrowing 3
- This differs from communicating post-infectious hydrocephalus and requires careful imaging assessment 3
- Particularly common in Africa (28% of pediatric cases) and South Asia (23.2% of cases) 5, 3
Post-hemorrhagic hydrocephalus in premature infants:
- Intraventricular hemorrhage (IVH) affects 15-20% of infants weighing less than 1500g at birth 3, 4
- Approximately 76% of infants with Grade III IVH develop post-hemorrhagic ventricular dilation 3
- Blood products can cause obstructive clots in the aqueduct or fourth ventricular outlets 4
- About 15% require permanent shunt placement 3
Trauma can cause obstructive hydrocephalus through:
Regional Variations in Pediatric Etiology
The distribution of causes varies significantly by geography:
- East Asia: Non-postinfectious congenital causes predominate (38.3% of cases) 3
- South Asia: Post-infectious causes are most common (23.2%) 3
- Africa: Post-infectious hydrocephalus is the single most common cause (28%) 5
- High-income countries: Congenital causes represent 36.7% of cases 3
Geriatric Population
Tumor-Related Obstruction
Primary brain tumors in older adults causing obstruction include:
- Gliomas affecting the third ventricle or aqueduct
- Colloid cysts of the third ventricle causing intermittent obstruction
- Pineal region masses 6
Metastatic disease can cause obstruction when:
- Parenchymal metastases compress ventricular pathways
- Leptomeningeal metastases create focal obstructions while maintaining some CSF communication 6
Vascular Causes
Hemorrhage in elderly patients:
- Intraventricular hemorrhage from hypertensive bleeds
- Subarachnoid hemorrhage with blood products obstructing CSF pathways 6
Infectious Causes
Coccidioidal meningitis causes hydrocephalus in approximately 40% of affected individuals, either at presentation or during disease progression 6.
Neurocysticercosis with subarachnoid involvement can cause obstructive hydrocephalus when cysts obstruct ventricular pathways 6.
Critical Diagnostic Distinctions
Differentiating Obstructive from Communicating Hydrocephalus
Phase-contrast MRI and T2-weighted cinematic CSF flow studies are essential for:
- Identifying aqueductal webs and subtle obstructions 1
- Assessing CSF dynamics and flow patterns 1
- Distinguishing true obstruction from impaired absorption 6
Key imaging findings for obstruction:
- Tri-ventricular hydrocephalus (lateral and third ventricles enlarged, fourth ventricle normal) suggests aqueductal stenosis 1
- Fourth ventricular enlargement with obstruction at the outlets 4
- Periventricular edema suggesting acute obstruction 4
Clinical Presentation Differences
Acute obstructive hydrocephalus presents with:
- Rapid onset within hours to days 7
- Severe headache, often described as "worst headache of life" 7
- Altered consciousness ranging from confusion to coma 7
- Papilledema from increased intracranial pressure 7
- Parinaud's syndrome (upward gaze palsy) with aqueductal or pineal region lesions 7
Infants with obstruction show:
- Progressive head circumference increase (macrocephaly) 7, 3
- Bulging, tense fontanelle 7, 3
- Splaying of cranial sutures, especially sagittal 7, 3
- "Sunset eyes" with downward eye deviation 7
- Apnea and bradycardia episodes 3
Common Pitfalls
Misclassifying post-infectious hydrocephalus: Approximately 20% of hydrocephalus cases have unclear etiology, and distinguishing obstructive from communicating post-infectious types requires careful assessment of aqueduct patency and history of febrile illness 3.
Missing aqueductal webs: These rare obstructions can present late in childhood or adolescence and require specific MRI sequences (phase-contrast, T2-weighted cine) for diagnosis 1.
Delayed tumor diagnosis: In resource-limited settings, brain tumors causing obstruction are frequently diagnosed late, increasing morbidity and mortality 5.
Assuming all post-hemorrhagic hydrocephalus is communicating: While most post-hemorrhagic hydrocephalus involves impaired CSF absorption, acute blood clots can cause true ventricular obstruction requiring different management 4.