Routine Neurosonography in Preterm Infants
All preterm infants born at ≤31 weeks and 6 days gestation should receive routine head ultrasound screening, with initial imaging in the first 7-14 days to detect hemorrhage, followed by repeat imaging at 4-6 weeks of age to identify white matter injury. 1
Screening Protocol by Gestational Age
Very Preterm Infants (≤31+6 weeks)
- Mandatory routine screening regardless of clinical course, birth weight, or initial study results 1
- First ultrasound: Days 7-14 of life to detect germinal matrix hemorrhage and intraventricular hemorrhage (IVH) 1
- Second ultrasound: 4-6 weeks of age to detect periventricular leukomalacia (PVL) and persistent ventricular enlargement 2, 1
- This two-scan minimum is essential because initial normal studies do not exclude late-developing abnormalities—55% of infants with cystic PVL and 26% with persistent ventricular enlargement had normal initial scans 2
Moderate Preterm Infants (32+0 to 36+6 weeks)
- Selective screening only in the presence of specific risk factors for intracranial hemorrhage or ischemia 1
- Risk factors include: hypoxic-ischemic injury, clinical seizures, abnormal neurological examination, or complicated clinical course 3
Rationale for Serial Imaging
The timing of repeat imaging at ≥4 weeks is critical because cystic PVL typically manifests 2-4 weeks after the initial insult and would be missed on early screening alone 2. Clinical course severity does not reliably predict which infants will develop cystic PVL, though it better predicts persistent ventricular enlargement 2.
What Ultrasound Detects
Cranial ultrasound reliably identifies:
- Intraventricular hemorrhage (Grades I-IV) within the lateral ventricles 3
- Severe periventricular leukomalacia with cyst formation 3
- Hydrocephalus and ventricular dilation 3
- White matter changes including cystic periventricular leukomalacia 3
These findings are particularly important because 16% of extremely preterm infants develop severe IVH, and approximately one-third of infants with IVH develop posthemorrhagic ventricular dilation 3
Critical Limitations and When to Consider MRI
Ultrasound significantly underdetects several important abnormalities:
- Cerebellar hemorrhage: Ultrasound detects only 23% of cerebellar hemorrhages identified on MRI, yet these lesions confer a 5-fold increased risk of abnormal neurological outcomes 3
- Diffuse white matter injury: The most common current form of white matter damage is difficult to visualize with ultrasound 3
- Hypoxic-ischemic injury: Ultrasound has low sensitivity for this most common cause of neonatal seizures 3
- Small infarctions and cortical malformations: These require MRI for detection 3
Term-equivalent MRI provides much more reliable neurological prognosis than cranial ultrasonography and should be considered for infants at highest risk, particularly those with severe IVH or abnormal neurodevelopmental trajectory 3
Common Pitfalls to Avoid
- Do not limit screening to only the smallest or sickest infants: Larger preterm infants (30-32 weeks) comprised 36% of those with cystic PVL and 21% of those with persistent ventricular enlargement in one series 2
- Do not rely solely on early imaging: Late abnormalities develop in a substantial proportion of infants with initially normal scans 2
- Do not assume clinical stability excludes pathology: Clinical course does not reliably predict development of cystic PVL 2
- Recognize ultrasound's blind spots: Consider MRI when clinical suspicion remains high despite normal ultrasound, particularly for cerebellar injury or subtle white matter abnormalities 3
Prognostic Implications
Ultrasound findings directly impact long-term outcomes and guide intervention decisions 3. Infants with detected abnormalities require: