25.1 Neonatal Head, Spine & Hip Sonography

Sonography is the first-line imaging tool for the neonatal brain, spine, and hips because these structures are incompletely ossified, leaving acoustic windows that disappear with age. No ionizing radiation, bedside portability, and real-time dynamic assessment make ultrasound ideal for critically ill infants in the neonatal intensive care unit.

Neonatal Cranial Sonography

Technique

The anterior fontanelle serves as the primary acoustic window; it typically remains open until roughly 9-18 months of age, but diagnostic imaging is most reliable in the first weeks of life. Use a small-footprint, high-frequency transducer (a sector, vector, or tightly curved array of about 7.5-10 MHz or higher) that fits the fontanelle and still penetrates the posterior fossa. The infant is imaged supine, often in the bassinet or incubator, with warmed gel.

Standard imaging is performed in two orthogonal planes:

• Coronal plane: a series of angled sweeps from the frontal lobes anteriorly through the third ventricle, the level of the foramen of Monro, and back to the trigones and periventricular white matter
• Sagittal and parasagittal planes: midline images show the corpus callosum, cavum septi pellucidi, third ventricle, and vermis; angled parasagittal images on each side display the caudothalamic groove, the lateral ventricle, and the periventricular white matter

The caudothalamic groove view is the single most important image because it contains the germinal matrix.

Germinal Matrix Hemorrhage

The germinal matrix is a highly vascular, fragile bed of subependymal tissue located in the caudothalamic groove (the junction of the caudate head and thalamus). It involutes by about 32-34 weeks of gestation, so germinal matrix hemorrhage (GMH) is overwhelmingly a disease of premature infants, with risk and severity increasing as gestational age decreases. Screening cranial ultrasound is routinely performed in the first week of life in infants born before about 30-32 weeks.

Grading follows the classic Papile system:

Two exam points matter here. First, the distinguishing feature between grade II and grade III is ventricular dilatation, not the amount of blood. Second, grade IV is now understood as a hemorrhagic venous infarction of the periventricular white matter caused by obstruction of the terminal veins, not a simple extension of subependymal blood — but sonographically it appears as an echogenic parenchymal focus adjacent to the ventricle and is still reported as grade IV.

On imaging, acute hemorrhage is echogenic (bright). A grade I bleed appears as an ovoid echogenic focus at the caudothalamic groove. Intraventricular blood may layer in the occipital horn or cast the ventricle. Over days to weeks, clot becomes isoechoic and retracts, sometimes leaving a small cyst at the germinal matrix site.

Periventricular Leukomalacia and Hydrocephalus

Periventricular leukomalacia (PVL) is ischemic injury of the periventricular white matter watershed zones, also mainly in preterm infants. Early sonography shows increased periventricular echogenicity ("flaring"); to be considered abnormal the echogenicity should be at least as bright as the choroid plexus and persist. After 2-6 weeks, the injured tissue cavitates into small periventricular cysts, the hallmark of established PVL, which correlates with spastic diplegia and cerebral palsy.

Hydrocephalus is documented by measuring ventricular size at the level of the foramen of Monro on coronal images (ventricular index) and following serial scans. Posthemorrhagic hydrocephalus follows grade III bleeds when clot obstructs cerebrospinal fluid flow or reabsorption. Progressive enlargement, a ballooned third ventricle, and a resistant anterior fontanelle are clinical-sonographic correlates.

Choroid Plexus Cysts vs. Hemorrhage

The choroid plexus is normally echogenic and fills much of the lateral ventricle body and atrium (it is absent from the frontal and occipital horns). A choroid plexus cyst is a round, well-defined anechoic structure within the echogenic choroid, usually an incidental finding. Choroid plexus hemorrhage, by contrast, appears as irregular, nodular, asymmetric enlargement of the echogenic choroid, often with irregular clot extending into the adjacent CSF. The key differentiator: a cyst is anechoic and round; hemorrhage is echogenic, irregular, and may extend beyond the choroid contour.

Neonatal Spine Sonography

Before the posterior elements ossify (the window narrows after about 3-6 months), the spinal canal is visible through the cartilaginous posterior arches with a high-frequency linear transducer. The exam is requested for sacral dimples, anorectal or cloacal anomalies, and suspected occult dysraphism.

• The conus medullaris in a term neonate should terminate at or above the L2-L3 level; a conus ending below L2-L3 is low-lying and suggests a tethered cord
• Real-time observation should show gentle, rhythmic pulsatile motion of the nerve roots with cardiac and respiratory cycles; a tethered cord shows damped or absent movement
• The filar cyst is a small, fusiform, midline anechoic cyst within the proximal filum terminale; it is a benign, incidental finding with no clinical consequence. Do not equate it with the ventriculus terminalis, a separate benign variant that is a focal dilatation of the central canal within the conus medullaris itself
• A thickened, echogenic filum terminale (greater than about 2 mm) and a dorsally positioned conus also support tethering

Once ossification progresses, ultrasound's role becomes limited and MRI takes over.

Developmental Dysplasia of the Hip

Developmental dysplasia of the hip (DDH) ranges from a shallow acetabulum to frank dislocation. Sonography is the study of choice from about 4-6 weeks of age (scanning earlier produces false positives from physiologic laxity, so it is deferred unless the physical exam is abnormal) through about 4-6 months, before the femoral head ossific nucleus blocks sound. Classic risk factors are breech presentation, female sex (affected several times more often than males), and a positive family history; first-born status, oligohydramnios, and tight swaddling with extended hips add risk.

The Graf Method

The Graf method is a static coronal evaluation with the infant in a lateral decubitus position and the hip in neutral or slight flexion. The coronal image must show a straight iliac line, the bony acetabular roof, and the labrum. Two angles are measured:

• Alpha angle: formed by the vertical baseline of the ilium and the bony roof line. It reflects osseous coverage. An alpha angle of 60 degrees or greater is normal (Graf type I). Values of 50-59 degrees indicate physiologic immaturity in an infant under 3 months (type IIa); 43-49 degrees is borderline dysplasia (type IIc); below 43 degrees indicates dysplasia with decentration (types III and IV)
• Beta angle: formed by the iliac baseline and the cartilaginous roof (labral) line. It reflects the cartilaginous roof. A beta angle under 55 degrees is normal; an increasing beta angle tracks the femoral head's lateral migration, and values above about 77 degrees accompany dislocation

The femoral head coverage (percentage of the head medial to the iliac baseline, the Morin method) should be at least 50% in a normal hip; coverage below 50% indicates subluxation.

Dynamic Stress Imaging

The dynamic (Harcke) component flexes the hip to 90 degrees and applies stress in the transverse plane, sonographically correlating with the clinical maneuvers:

• Barlow maneuver: adduction with posterior pressure, testing whether a located hip can be dislocated posteriorly
• Ortolani maneuver: abduction with anterior lifting, testing whether a dislocated hip can be reduced

Under ultrasound, a positive stress test shows the femoral head sliding laterally and posteriorly from the triradiate cartilage during stress and relocating when stress is released. Both static morphology (Graf) and dynamic stability are documented in the report.