What are the causes of hydrocephalus in adults?

Causes of Hydrocephalus in Adults

In adults, the most common causes of hydrocephalus are brain tumors, subarachnoid hemorrhage, traumatic brain injury, meningitis, and normal pressure hydrocephalus (NPH), with space-occupying lesions requiring immediate evaluation as they represent a critical and treatable etiology. 1

Obstructive Hydrocephalus Causes

Neoplastic Etiologies

• Primary brain tumors such as gliomas and colloid cysts of the third ventricle can directly obstruct CSF pathways 1
• Metastatic disease causes obstruction through two mechanisms: parenchymal metastases compressing ventricular pathways or leptomeningeal metastases creating focal obstructions 1
• Brain tumors represent a major acquired cause requiring urgent evaluation, particularly in middle-aged adults where non-postinfectious hydrocephalus occurs more frequently with increasing age 1

Hemorrhagic Causes

• Subarachnoid hemorrhage is one of the most frequent causes of adult-onset hydrocephalus, with blood products obstructing CSF pathways 1, 2
• Intraventricular hemorrhage from hypertensive bleeds can cause acute obstruction in elderly patients 1
• The pathophysiology involves reduced CSF reabsorption by arachnoid granulations affected by blood products 3

Traumatic Etiologies

• Traumatic brain injury disrupts normal CSF flow patterns and absorption mechanisms, leading to both obstructive and communicating hydrocephalus 4, 3
• Adult-onset external hydrocephalus specifically relates to traumatic injuries through rupture of the arachnoid membrane, allowing fluid accumulation in the subarachnoid and subdural spaces 3

Infectious Causes

• Meningitis (both infectious and non-infectious) leads to hydrocephalus through meningeal inflammation and subsequent impairment of CSF circulation 4
• Neurocysticercosis can cause hydrocephalus through mechanical obstruction of ventricles or basal cisterns by cysts themselves or by inflammatory reaction (ependymitis and/or arachnoiditis) 5
• The racemose variety of neurocysticercosis occurs in ventricles or basal cisterns with abnormal growth of cystic membranes, following a progressive course even after ventricular shunting 5

Structural Abnormalities

• Aqueductal stenosis can be congenital with late onset or acquired from prior infection or inflammation 2
• Aqueductal webs and subtle obstructions require phase-contrast MRI and T2-weighted cinematic CSF flow studies for identification 1

Normal Pressure Hydrocephalus (NPH)

Primary Causes of NPH

• Traumatic brain injury disrupts CSF flow patterns and absorption mechanisms 4
• Intracranial hemorrhage, particularly subarachnoid hemorrhage, impairs CSF circulation 4
• Meningitis leads to NPH through meningeal inflammation 4
• Venous sinus thrombosis alters CSF dynamics 4
• Vasculitis affects CSF production and absorption 4

Pathophysiological Mechanisms

• Disruption of normal CSF circulation patterns leads to ventricular enlargement and decreased CSF absorption 4
• Interstitial edema contributes to white matter damage 4
• Ischemic damage occurs in white matter from compromised blood flow 4
• Inflammatory processes, including neuroinflammation, play a central role 4

Associated Systemic Conditions

• Systemic Lupus Erythematosus (SLE) has been linked to NPH through inflammatory processes and vasculitis contributing to increased CSF volume 4
• Alzheimer's disease is a common comorbidity affecting 20-57% of NPH cases and significantly impacts response to shunting when moderate to severe disease burden is present 4

Surgical and Iatrogenic Causes

• Neurosurgical treatment of aneurysms can lead to adult-onset external hydrocephalus through arachnoid membrane disruption 3
• Post-surgical hydrocephalus involves three essential factors: intracranial bleeding, tearing of the arachnoid membrane, and excessive CSF quantity from reduced reabsorption 3

Diagnostic Approach

Critical Imaging Considerations

• MRI without IV contrast is the preferred imaging modality for NPH diagnosis 4
• Phase-contrast MRI and T2-weighted cinematic CSF flow studies are essential for identifying aqueductal webs, assessing CSF dynamics, and distinguishing true obstruction from impaired absorption 1
• Key radiological findings for NPH include ventriculomegaly, narrowed posterior callosal angle, effaced sulci, widened sylvian fissures, and periventricular white matter changes 4

Clinical Presentation Patterns

• Acute obstructive hydrocephalus presents with rapid onset severe headache, altered consciousness, papilledema, and Parinaud's syndrome 1
• Chronic hydrocephalus may present with a syndrome resembling NPH regardless of underlying etiology 2, 6

Common Pitfalls

• The degree of CSF reabsorption impairment conditions prognosis more than the volume of fluid accumulation itself 3
• Approximately 20% of hydrocephalus cases have unclear etiology, making thorough diagnostic evaluation critical 7
• Patients with NPH and moderate to severe Alzheimer's disease burden are significantly less likely to respond to shunting, requiring careful patient selection 4