Ventricular Index in Infants: Normal Values and Clinical Management
The ventricular index (VI) should be measured from the lateral wall of the lateral ventricle to the falx in the axial plane, with normal values ranging from approximately 8.7-24.7 mm for the thalamo-occipital distance in preterm infants (23-33 weeks gestation), and anterior horn width should not exceed 2.9 mm. 1, 2
Normal Ventricular Index Values
Preterm Infants (23-33 weeks gestation)
- Anterior horn width (AHW): 0-2.9 mm 2
- Thalamo-occipital distance: 8.7-24.7 mm 2
- VI measurements show a general trend to increase slightly with advancing postmenstrual age from 23 to 45 weeks 3
- The frontal horn ratio (FHR) remains relatively stable at a median of 0.31 across gestational ages 3
Term Infants
- There is a significant difference in mean VI values between preterm and term infants, with term infants having larger measurements 4
- Small for gestational age infants have significantly different ventricular sizes compared to appropriate gestational age infants of corresponding gestational ages 4
Measurement Technique and Reliability
The VI should be measured in the axial plane through the temporoparietal bone from the lateral wall of the body of the lateral ventricle to the falx 1. This measurement correlates closely with coronal plane measurements 1.
Key Technical Points:
- AHW and VI demonstrate high inter-observer reliability (ICC 0.49-0.84 for VI, 0.51-0.81 for AHW) when performed by experienced clinicians 5
- FTHR shows lower reliability (ICC 0.41-0.82) and is less recommended 5
- Head position during scanning does not significantly affect lateral ventricle measurements 2
- Sex does not influence ventricular size 2
Interpretation of Abnormal Measurements
Defining Post-Hemorrhagic Ventricular Dilatation (PHVD)
Hydrocephalus can be defined as the atrium of the lateral ventricle measuring >10 mm on horizontal plane ultrasound or the body of the lateral ventricle at the level of the midthalamus measuring >10 mm on sagittal imaging 6.
Severity Classification Using Ventricular/Biparietal (V/BP) Ratio:
- Mild hydrocephalus: V/BP ratio 0.26-0.40 6
- Moderate hydrocephalus: V/BP ratio 0.40-0.60 6
- Severe hydrocephalus: V/BP ratio 0.60-0.90 6
- Extreme hydrocephalus: V/BP ratio 0.91-1.0 6
Important caveat: Cortical mantle thickness is NOT a statistically significant indicator of neurodevelopmental outcome, as several infants with extreme hydrocephalus can display normal motor development 6.
Management of Abnormal Ventricular Measurements
Predictive Value for Surgical Intervention
AHW from the second week of life onwards is the strongest predictor for requiring surgical intervention for severe PHVD (AUC 0.86-0.96), slightly superior to VI (AUC 0.80-0.96) 5. Serial measurements starting from day 14 provide the most reliable prognostic information 5.
Surgical Temporizing Measures
When intervention is required, ventricular access devices (VADs), external ventricular drains (EVDs), ventriculosubgaleal (VSG) shunts, or lumbar punctures are treatment options, with clinical judgment required for selection 6.
VSG shunts reduce the need for daily CSF aspiration compared with VADs 6, and VADs reduce morbidity and mortality compared with EVDs 6.
What NOT to Do
Serial lumbar puncture should NOT be routinely used to reduce the need for shunt placement or prevent progression of hydrocephalus in premature infants 6. This is a Level I recommendation with high clinical certainty, as lumbar puncture neither predicts nor prevents the need for permanent VP shunt placement 6.
Clinical Monitoring Algorithm
- Obtain baseline cranial ultrasound within first 3-6 days of life 2
- Measure AHW and VI using standardized technique in axial plane 1, 2
- For infants with intraventricular hemorrhage, perform serial measurements at days 4-7, day 14, and 36 weeks postmenstrual age 5
- From the second week onwards, prioritize AHW measurements as the most reliable predictor of need for intervention 5
- If AHW >2.9 mm or VI exceeds gestational age-specific norms, calculate V/BP ratio to assess severity 6, 2
- Consider surgical temporizing measures based on progressive ventricular enlargement and clinical status, NOT based on routine serial lumbar punctures 6