Sonographic Features of Raised Intracranial Pressure in Infant Brain Parenchyma
On neurosonography in infants, raised intracranial pressure manifests primarily through ventricular measurements (anterior horn width >6mm, ventricular index >97th percentile + 4mm), combined with Doppler findings showing increased intracranial-to-extracranial internal carotid artery flow velocity ratios and elevated resistance indices.
Key Parenchymal and Ventricular Measurements
The most reliable sonographic indicators of raised ICP in infants involve specific quantitative measurements 1:
Ventricular Parameters
Anterior Horn Width (AHW): Most sensitive early marker
- Normal: <3mm
- Abnormal: >6mm
- AHW changes earlier than ventricular index, making it superior for detecting early ICP elevation 1
Ventricular Index (Levene): Measured from midline falx to lateral aspect of anterior horn at foramen of Monro level
- Intervention threshold: 97th percentile + 4mm for gestational age
- At 27 weeks: 14mm; 31 weeks: 15mm; 33 weeks: 16mm 1
Combined Criteria: AHW >4mm + thalamooccipital dimension >26mm + third ventricle width >3mm suggests posthemorrhagic ventricular dilation with raised pressure 1
Doppler Sonographic Signs
Spectral Doppler provides critical functional assessment of raised ICP 2, 3, 4:
Flow Velocity Changes
- Increased intracranial/extracranial ICA ratio: Peak systolic velocity in intracranial internal carotid artery increases relative to extracranial segment—this is an early, sensitive marker 3, 4
- Elevated resistance index (RI): Increases from normal ~0.63 to >0.73 with raised pressure 5, 4
- Elevated pulsatility index (PI): Increases from ~1.0 to >1.3 5
- Decreased end-diastolic flow velocities: Particularly evident during fontanelle compression, indicating abolished cranial compliance 4
Transsystolic Time (TST)
- TST measurement: Strongly correlates with ICP (p<0.005)
- Decreases from normal ~221ms to ~176ms with elevated pressure
- More reliable than PI or RI as it relates solely to intracranial physical properties 5
Parenchymal Echogenicity Changes
Direct parenchymal findings indicating raised ICP 3, 6:
- Increased parenchymal echogenicity: Haziness of brain substance edges
- Depressed vascular pulsations: Focal or universal depression of Circle of Willis, anterior cerebral artery, and middle cerebral artery pulsations visible on real-time imaging
- These findings indicate more severe parenchymal damage and impaired intracranial blood flow 6
Clinical Integration Algorithm
Combine measurements for optimal sensitivity 1:
First-line screening: Measure AHW on every scan
- If >6mm → high suspicion for raised ICP
- If 3-5mm → equivocal, add Doppler assessment
Add ventricular index if AHW abnormal
- Compare to gestational age-specific norms
Perform Doppler evaluation when ventricular measurements abnormal:
- Measure intracranial vs extracranial ICA velocities
- Calculate RI and PI
- Assess TST if available
Assess vascular pulsations on real-time imaging
- Look for depression of arterial pulsations
- Note any parenchymal echogenicity changes
Important Caveats
- Ventricular index is a late sign—AHW changes first, so relying solely on ventricular index may miss early raised ICP 1
- Occipital horn dilation may occur first in some infants (forme fruste colpocephaly), but its reliability as an ICP indicator is not established 1
- Clinical correlation is essential: Ultrasonographic measurements must be combined with physical examination findings (fontanelle fullness, suture splaying, apnea, bradycardia) for surgical decision-making 1
- Serial measurements are more valuable than single time points—progressive increases indicate worsening pressure 1
- Ventricular asymmetry is an anatomical variant and does not indicate pathology 1
The combination of quantitative ventricular measurements with Doppler flow assessment provides the most comprehensive non-invasive evaluation of raised ICP in infants, avoiding the need for invasive monitoring in most cases 2, 4.