What is the best approach to diagnose and manage a patient with suspected hydrocephalus, particularly in terms of CT (Computed Tomography) scan interpretation and subsequent treatment options?

CT Scan Interpretation for Hydrocephalus

Non-contrast CT head is the appropriate initial imaging modality for suspected hydrocephalus, providing rapid assessment of ventricular size and identifying acute complications, though MRI without contrast is superior for definitive diagnosis and characterizing underlying pathology. 1, 2, 3

Initial Imaging Approach

When to Use CT

• Order non-contrast CT head immediately for acute presentations with altered mental status, severe headache, or rapid neurological deterioration to quickly identify ventricular enlargement and rule out life-threatening complications like acute obstructive hydrocephalus or hemorrhage 1
• CT is particularly valuable in emergency settings due to rapid acquisition time, widespread availability, and high sensitivity for detecting acute blood and gross ventricular dilatation 4, 5
• Use low-dose CT protocols (0.29 mSv vs 2.2 mSv conventional) for serial monitoring of shunted hydrocephalus patients to minimize cumulative radiation exposure while maintaining diagnostic quality 6

Key CT Findings to Identify

Ventricular System Assessment:

• Measure ventricular size using linear measurements and ratios to quantify enlargement 7
• Assess for disproportionate ventricular enlargement relative to sulcal prominence 1, 7
• Evaluate frontal horn width and temporal horn dilatation 1

Additional Diagnostic Features:

• Periventricular hypodensity (transependymal CSF flow) indicating active hydrocephalus 1, 7
• Effaced sulci along high convexities with widened sylvian fissures 1, 2
• Narrowed posterior callosal angle 1, 2
• Shunt catheter position and integrity in previously treated patients 6

Critical Limitations of CT

CT cannot reliably distinguish hydrocephalus subtypes or predict treatment response 7, 3:

• No correlation exists between ventricular size on CT and CSF outflow resistance 7
• CT poorly differentiates communicating hydrocephalus from hydrocephalus ex vacuo (cerebral atrophy) 7
• Periventricular lucencies and ventricular-to-sulcal ratios correlate poorly with measured CSF dynamics 7
• CT cannot detect cerebral aqueduct flow void, a key finding for assessing CSF flow dynamics 1
• CT may miss small obstructing lesions along the ventricular system that could indicate non-communicating hydrocephalus 1

When MRI is Essential

Obtain MRI head without IV contrast for definitive diagnosis and treatment planning in non-emergent settings 1, 2, 3:

MRI Advantages Over CT

• Superior detection of interstitial edema and transependymal CSF flow 3
• Visualization of cerebral aqueduct flow void indicating patent CSF pathways 1, 2
• Better characterization of obstructive pathology throughout the CSF pathway 5
• Higher sensitivity for periventricular white matter changes 1
• Multiplanar imaging capability for better anatomic definition 3

Specific MRI Sequences to Request

• 3D T2-weighted sequences to evaluate CSF spaces and identify obstruction sites 5
• Phase-contrast cine MRI to assess CSF flow dynamics and aqueductal patency 5
• FLAIR sequences for periventricular white matter signal changes 5
• Gradient-echo T2 sequences* to detect prior hemorrhage or vascular malformations 5

Context-Specific Recommendations

Normal Pressure Hydrocephalus (NPH)

MRI without IV contrast is the preferred initial study for suspected NPH in adults presenting with the classic triad of gait disturbance, urinary incontinence, and cognitive impairment 1, 2:

• Look for ventriculomegaly with narrowed posterior callosal angle 1, 2
• Identify DESH pattern (disproportionately enlarged subarachnoid space hydrocephalus) 1, 2
• Assess for cerebral aqueduct flow void 1, 2
• CT can be used if MRI is contraindicated, but has lower sensitivity for characteristic NPH features 1, 2

Aneurysmal Subarachnoid Hemorrhage with Hydrocephalus

Patients with aneurysmal SAH and CT evidence of hydrocephalus that is clinically symptomatic require urgent external ventricular drain (EVD) placement 1:

• Non-contrast CT immediately identifies both SAH and associated hydrocephalus 1
• Follow-up imaging for delayed hydrocephalus should be directed by local protocols and clinical symptoms 1

Pediatric Hydrocephalus

• Ultrasound through open fontanelles is sufficient for initial assessment and serial monitoring in infants 4, 5
• MRI is the best modality to define obstruction nature and location in children, avoiding radiation exposure 4, 5
• CT should be reserved for acute presentations or when MRI is unavailable 4, 5

Common Pitfalls to Avoid

• Do not rely solely on CT findings to determine shunt candidacy - CSF dynamics studies are required for treatment decisions in NPH 7
• Do not assume normal CT excludes hydrocephalus - early or intermittent hydrocephalus may have subtle findings 5
• Do not use conventional CT protocols for serial monitoring - implement low-dose protocols to minimize cumulative radiation exposure 6
• Do not mistake hydrocephalus ex vacuo for treatable hydrocephalus - MRI and CSF dynamics testing are needed for differentiation 7, 3
• Absence of cortical sulci >3mm suggests compromised CSF absorption, but cortical atrophy does not rule out increased CSF outflow resistance 7