Neonatal Neurosonography According to AIUM 2024: Windows, Sections, Protocol

What the AIUM 2024 Practical Parameter Changes

AIUM Practice Parameter 2024 describes not a 'limited ultrasound through the large fontanelle,' but a full-fledged neurosonography for neonates and infants: indications, transducer selection, mandatory planes, additional acoustic windows, Doppler modes, documentation, and reporting requirements. The document updates the 2020 edition and is convenient as a checklist for neonatal intensive care units, ultrasound rooms, and perinatal centers.

Key idea: the anterior fontanelle remains the main window, but not the only one. In cases of suspected intraventricular hemorrhage, pathology of the occipital horns, cerebellum, fourth ventricle, vascular abnormalities, or limited visualization, it is necessary to expand the study through the posterior, mastoid, and, if necessary, other accessible windows.

Indications: When NSG is Justified

AIUM broadly formulates indications: the study is performed for a valid clinical reason. Typical indications include prematurity, suspected intracranial hemorrhage, seizures, apnea, bradycardia, signs of hypoxic-ischemic injury, congenital infections, congenital anomalies, dysmorphia, abnormal head size or growth, suspected hydrocephalus, post-intervention monitoring, and dynamic observation of known findings.

For practice, it is important to distinguish between screening and diagnostic study. Screening in clinically stable preterm infants is conducted according to an age schedule; diagnostic NSG is performed immediately upon deterioration, neurological symptoms, rapid head circumference increase, or suspected complications.

Screening of Preterm Infants: AIUM Timing

Equipment and Settings

A transducer is used that physically fits on the fontanelle and provides maximum resolution with sufficient penetration depth. Typically, the main series is performed with a sector or microconvex transducer; a high-frequency linear transducer is useful for superficial structures, interhemispheric fissure, subarachnoid spaces, cortex, and convexital surface.

Depth, focus, gain, dynamic range, and frequency should allow visualization from the near cortical surface to the posterior fossa without loss of contrast. Excessive gain masks small hemorrhages, while too low gain mimics expansion of cerebrospinal fluid spaces. Images are saved in standard planes with side and window labeling.

Anterior Fontanelle: Basic Coronal Series

Coronal sections through the anterior fontanelle are performed sequentially from anterior to posterior. The protocol should include the frontal lobes and anterior horns of the lateral ventricles, the region of the foramen of Monro and third ventricle, bodies of the lateral ventricles, thalami, choroid plexuses, atria, occipital regions, and periventricular white matter.

At each level, symmetry, ventricular shape, echogenicity of the germinal matrix in the caudothalamic groove, condition of the choroid plexuses, periventricular echogenicity, presence of hemorrhagic foci, cysts, mass effect, and midline shift are assessed. In preterm infants, it is especially important not to limit to a single section through the ventricles: small hemorrhages and early white matter changes are easily missed with an incomplete series.

Anterior Fontanelle: Sagittal and Parasagittal Series

The mid-sagittal section documents the corpus callosum, septum pellucidum, third ventricle, aqueductal region, fourth ventricle, vermis of the cerebellum, cisterna magna, and brainstem landmarks. This section is needed not only to exclude gross malformations: it helps to understand whether ventriculomegaly is associated with obstruction, atrophy, or post-hemorrhagic changes.

Parasagittal sections are performed on both sides through the caudothalamic groove, lateral ventricles, and periventricular white matter to the lateral parts of the hemispheres. Comparison of the right and left sides is mandatory: asymmetry of echogenicity, local bulging of the choroid plexus, irregular ventricular contour, or focal increase in echogenicity in the white matter should be described, even if ventricular sizes are not increased.

Additional Windows: When They Are Mandatory

The posterior fontanelle improves the assessment of the occipital horns, atria of the lateral ventricles, and intraventricular blood, especially if the posterior parts are insufficiently visualized through the anterior fontanelle. This window is useful for questionable findings in the choroid plexuses and for monitoring small intraventricular clots.

The mastoid, or posterolateral, window is necessary for the posterior fossa: cerebellum, fourth ventricle, cisterna magna, and retrocerebellar spaces. Through the anterior fontanelle, the cerebellum is often located in the far zone and partially shielded; therefore, cerebellar hemorrhages and posterior fossa changes may be underestimated without mastoid access.

Anterior-lateral and temporal windows are used as needed, mainly for vascular assessment and clarification of basal structures. The set of windows should not be formal but diagnostically sufficient: if the standard series does not answer the clinical question, the study is expanded.

Doppler Modes

Color, power, and spectral Doppler are used to assess patency and direction of blood flow, vascular malformations, venous sinuses, major arteries of the brain base, and dynamics in hydrocephalus or critical conditions. Doppler does not replace grayscale NSG: first, an anatomical map is obtained, then the vascular component is clarified.

When working with neonates, the principle of reasonable minimal exposure applies. The duration of the Doppler mode and acoustic power are chosen as low as compatible with the diagnostic task; this is especially important in extremely preterm and unstable infants.

What Must Be Described in the Report

The report should include the indication, accesses and limitations, comparison with previous studies, condition of the ventricular system, interhemispheric fissure, and extra-axial spaces, hemispheric parenchyma, periventricular white matter, germinal matrix, choroid plexuses, corpus callosum, posterior fossa, and cerebellum. If Doppler is performed, the vessels studied and diagnostically significant flow characteristics are described.

Hemorrhages should be anatomically localized: germinal matrix, ventricles, parenchyma, cerebellum, subdural or subarachnoid space. In ventriculomegaly, it is important to indicate its dynamics and association with intraventricular blood, parenchymal thinning, or signs of obstruction. The wording should help the neonatologist decide whether follow-up, neurosurgical consultation, or additional MRI is needed.

Typical Protocol Errors

• Limiting the study to the anterior fontanelle when addressing the posterior fossa or occipital horns.
• Absence of parasagittal sections through the caudothalamic grooves in preterm infants.
• Description 'ventricles not enlarged' without assessing white matter and evolution of echogenicity.
• Insufficient side and window labeling, making dynamic comparison unreliable.
• Using Doppler without prior quality grayscale series.

Practical Checklist for Execution

1. Check indication, gestational and postnatal age, previous NSG.
2. Start with the anterior fontanelle: complete coronal series from front to back.
3. Perform mid-sagittal and bilateral parasagittal sections.
4. Add posterior fontanelle for atria and occipital horns if it improves diagnosis.
5. Add mastoid window for cerebellum and fourth ventricle.
6. Apply Doppler according to clinical task with minimally sufficient exposure.
7. Save representative images of all windows and provide a structured report.