Paediatric Ultrasound
In children, ultrasound is frequently the first-line imaging test — it uses no ionising radiation, needs no sedation, is portable to the cot-side and gives real-time, dynamic answers. This deep-dive covers the paediatric-specific technique, the normal measurements that differ from adults, and the high-yield thresholds for the conditions ultrasound is asked to settle: developmental hip dysplasia, pyloric stenosis, intussusception, the acute abdomen, the neonatal brain and spine, and the renal tract. Pick a topic on the left.
Paediatric thresholds are age-dependent — follow local protocols and specialist supervision. The measurement cut-offs on this page (Graf angles, pyloric wall/channel, appendiceal diameter, conus level, hydronephrosis grades) are widely-cited teaching values, but paediatric norms vary with gestational and postnatal age, machine and technique. Several conditions here (DDH, HPS, intussusception, midgut volvulus, testicular torsion) are time-critical — a normal or equivocal scan does not exclude disease and must be interpreted alongside the clinical picture. Neonatal and paediatric ultrasound should be performed and reported under appropriate paediatric-radiology supervision, following your department’s protocol book. Nothing here replaces supervised, hands-on training.
Principles of ultrasound in children
Children are not small adults. Their smaller, less-ossified, less-fatty bodies actually make them ideal ultrasound subjects — acoustic windows are better and higher-frequency probes give exquisite resolution. The main variable you are managing is a small, moving, sometimes frightened patient.
Free Why ultrasound is first-line in paediatrics
The single biggest driver. Children are more radiosensitive and have a longer lifetime to express any radiation-induced malignancy, so ALARA and the “Image Gently” principle push US and MRI ahead of CT/fluoroscopy wherever they can answer the question — hips, pylorus, intussusception, brain (through the fontanelle), spine, kidneys and testes are all US-first.
Compressibility (appendix, bowel), peristalsis, cord pulsation, joint stability manoeuvres (Barlow/Ortolani) and colour-flow perfusion (testis, bowel) are all assessed live — information a static CT slice cannot give.
Scans go to the sick neonate in the incubator or the child on the ward, avoiding transfer of an unstable patient.
Because it is quick and painless, US usually avoids the sedation or general anaesthetic that paediatric CT/MRI may require — a real safety and throughput advantage.
Trade-off: ultrasound is operator-dependent and window-limited (bowel gas, dressings, bony coverage as the fontanelle closes ~ 9–18 months). Where US cannot answer, MRI is the usual radiation-free next step.
Free Transducer & machine choice
Small patients sit close to the transducer, so you can use higher frequencies for better resolution and accept the shallower penetration. Typical choices: high-frequency linear (up to ~12–18 MHz, some to 22 MHz) for hips, pylorus, appendix, superficial bowel, neonatal spine, testes and small parts; a small-footprint curvilinear/microconvex for deeper abdomen and larger children; a neonatal sector/phased or high-frequency linear through the anterior fontanelle for the brain. Match probe footprint to the acoustic window (a big adult curvilinear will not fit a neonatal flank).
Use a paediatric preset if available; place the focal zone at the region of interest; keep depth shallow to maximise line density and frame rate; use harmonics/compounding to reduce artefact.
Keep to ALARA acoustic-output principles, especially for neonatal cranial/spinal and any Doppler over developing tissue — minimise dwell time and output.
Free Comfort, distraction & the moving target
A cold probe or gel makes an infant cry and tense — warm both. Keep the child warm (neonates lose heat fast) and, where possible, allow a parent to stay in contact.
For pyloric and abdominal scans a feed (or dummy/sucrose) settles the infant and can fill the stomach as an acoustic window; swaddling and cuddle-holds reduce movement.
Toys, phones/tablets, bubbles, play specialists and letting an older child hold the gel bottle all improve cooperation and image quality — engagement is a technique, not a nicety.
Have your images and measurements planned so scanning is quick — the diagnostic window in a wriggling infant is short.
Key point Normal paediatric measurements differ
| Structure | Paediatric threshold / norm | See tab |
|---|---|---|
| Hip — Graf alpha angle | ≥60° = mature (Type I) bony roof | Hip / DDH |
| Pylorus — muscle wall | ≥3 mm thickness | HPS |
| Pylorus — channel length | ≥15–17 mm | HPS |
| Appendix — outer diameter | >6 mm non-compressible | Abdomen |
| Conus medullaris tip | Normal at L1–L2; below L2–L3 abnormal | Spinal |
| Filum terminale | Thickened if >2 mm | Spinal |
| Renal pelvis / SFU | SFU grade 0–4 | Renal |
Developmental dysplasia of the hip (DDH)
Hip ultrasound is the imaging standard for the infant hip before the femoral head ossifies (~ 4–6 months). The Graf technique gives a reproducible, angle-based morphological classification; a dynamic component (Barlow/Ortolani under US) assesses stability. Screening is typically done at around 6 weeks of age (or 4–6 weeks after a positive/uncertain clinical exam or a risk factor such as breech, family history or clinical instability).
Free The Graf standard plane & landmarks
Infant in lateral decubitus (or supine), hip flexed ~15–20°. Probe: high-frequency linear in the coronal plane over the lateral hip. The image is only valid when three landmarks are shown in one plane: a straight (horizontal) iliac line, the lower limb of the os ilium at the acetabular fossa, and the labrum.
The bony acetabular roof; its slope against the iliac baseline defines the alpha (α) angle — the measure of bony coverage/maturity.
The hyaline cartilage roof running out to the fibrocartilaginous labrum; its slope defines the beta (β) angle — how the cartilage roof is holding the head.
The proportion of the femoral head medial to (i.e. covered by) the bony acetabulum is a useful adjunct — roughly >50% coverage is reassuring; poor coverage suggests subluxation.
High yield Graf classification — alpha & beta angles
| Graf type | Alpha (α) | Beta (β) | Meaning |
|---|---|---|---|
| Type I (Ia/Ib) | ≥60° | Ia <55° / Ib >55° | Mature, normal hip |
| Type IIa (<3 mo) | 50–59° | — | Physiologically immature (age-appropriate if <12 wks; follow up) |
| Type IIb (>3 mo) | 50–59° | — | Delayed ossification — abnormal for age, treat |
| Type IIc | 43–49° | <77° | Critical zone, at-risk but concentric |
| Type D | 43–49° | >77° | Decentring / becoming eccentric |
| Type III | <43° | — | Subluxed — cartilage roof everted/upturned |
| Type IV | <43° | — | Dislocated — labrum displaced inferomedially |
Memory anchor: alpha ≥60° = normal (Type I). A falling alpha and rising beta together are the hallmark of dysplasia. Below ~12 weeks an alpha in the 50s can still be physiological immaturity (Type IIa) and should reach 60° by ~12 weeks; the same value after 3 months is pathological (Type IIb).
Dynamic Barlow / Ortolani under ultrasound
Graf morphology is static; adding a dynamic scan (often in the transverse/flexion view) shows how the head behaves under stress. Under real-time US you perform the clinical manoeuvres and watch the femoral head:
Adduct and posteriorly stress the flexed hip — a dislocatable hip shows the head displacing posteriorly out of the acetabulum on the screen.
Abduct and lift — a dislocated but reducible hip shows the head relocating into the acetabulum.
Quantify displacement by how much femoral-head coverage is lost during provocation; loss of a concentric position confirms instability.
Clinical Timing & when to treat
Scanning much before ~4–6 weeks over-calls physiological immaturity and laxity; the standard screening window is around 6 weeks. Selective screening targets breech presentation, positive family history and clinically unstable/abnormal hips.
Broadly: Type I — normal, no treatment. Type IIa — physiological, re-scan (e.g. at ~12 weeks) to confirm maturation. Type IIb and worse, and any unstable (Barlow/Ortolani positive) or decentred/dislocated hip (IIc/D/III/IV) — refer to paediatric orthopaedics; a Pavlik harness is the usual first-line abduction treatment in early infancy, with imaging follow-up. Local screening pathways vary — defer to them.
Caveat: Graf is technique-critical — a tilted plane falsely alters the angles. Persistent risk factors or clinical concern warrant repeat/expert assessment even with a “normal” alpha.
Hypertrophic pyloric stenosis (HPS)
The classic infant (typically 3–6 weeks old, often a first-born male) with progressive non-bilious projectile vomiting, a palpable “olive” and visible gastric peristalsis. Ultrasound has replaced the upper-GI contrast study as the test of choice — sensitivity ~97%, specificity approaching 100% — and directly measures the hypertrophied pyloric muscle.
Free Technique
Supine or right-posterior-oblique (RPO) — rolling the baby onto the right side brings gastric fluid into the antrum/pylorus, a good acoustic window. A recent feed (clear fluid or milk) fills the stomach and helps. Probe: high-frequency linear.
Locate the fluid-filled antrum to the right of midline, deep to the left lobe of liver and anterior to the pancreas/aorta; follow it to the pyloric canal. Image in both long axis (channel length) and short axis (target).
Observe for gastric emptying — in HPS the channel does not open and little/no fluid passes into the duodenum despite vigorous antral peristalsis (“non-emptying”).
Measure single muscle-wall thickness (not the full diameter) on the anterior wall in short axis, and canal length in long axis, when the pylorus is relaxed (not mid-contraction, which falsely lengthens it).
High yield Diagnostic measurements & signs
| Feature | Threshold for HPS | Note |
|---|---|---|
| Single muscle-wall thickness | ≥3 mm | The most reliable single measure |
| Pyloric channel length | ≥15–17 mm | Some texts use ≥16–18 mm |
| Non-emptying | No relaxation / no passage of fluid | Dynamic, real-time finding |
Values are age- and size-dependent; borderline figures (especially in the very young or premature) should be re-scanned. “Don’t let the numbers fool you” — dynamic non-emptying with vigorous peristalsis supports the diagnosis even when a measurement is borderline.
Short-axis view: the hypertrophied hypoechoic muscle ring surrounds the echogenic mucosa/lumen — a target/doughnut.
Long axis: the thickened pylorus indents the fluid-filled antrum, resembling a cervix protruding into the vaginal fornices (“cervix” or “nipple” sign).
The elongated hypertrophied pylorus is the palpable epigastric “olive” felt clinically — you are imaging the same structure.
Redundant antral mucosa can prolapse; you will see energetic antral waves that stop at the closed channel.
Intussusception
Telescoping of proximal bowel into distal bowel — most commonly ileocolic in the 3-month to 3-year age group, presenting with intermittent colicky pain, drawing up the legs, vomiting and (late) “redcurrant-jelly” stool. Ultrasound is both the diagnostic test of choice and the tool that guides and monitors non-operative reduction.
Free Technique & where to look
High-frequency linear probe; scan the whole colon, starting in the right upper quadrant / subhepatic region where the ileocolic intussusception classically lodges, then across the transverse colon. Graded compression clears gas.
A true ileocolic intussusception is a bulky mass (often >2.5 cm outer diameter). Small (<2 cm), transient small-bowel–small-bowel intussusceptions are common, often self-reduce and usually need no intervention.
High yield Signs
Transverse plane: concentric alternating hyper- and hypoechoic rings of telescoped bowel wall and mesenteric fat — the diagnostic target.
Longitudinal plane: the layered mass resembles a kidney (hypoechoic bowel wall around an echogenic mesenteric-fat “hilum”).
Look for a pathological lead point (enlarged node, Meckel diverticulum, polyp, duplication cyst, lymphoma, HSP-related haematoma) — more likely at the extremes of age or if recurrent.
Fluid trapped between the layers and absent colour Doppler flow in the intussusceptum wall indicate ischaemia — poor-prognosis signs that predict failed reduction and raise perforation risk.
Poor-prognosis markers: trapped intraluminal fluid, absent mural flow, a lead point, free fluid/free gas, or peritonism. These flag ischaemia/perforation risk and steer away from enema reduction toward surgery.
Management note Reduction
Confirmed ileocolic intussusception without contraindication is treated by image-guided non-operative reduction — either air (pneumatic) enema or hydrostatic (saline/water-soluble contrast) enema, performed by/with the paediatric radiology and surgical teams and monitored fluoroscopically or under ultrasound. Contraindications include perforation, peritonitis and shock, which mandate surgery. This page is a sonographic reference, not a reduction protocol — always follow local pathways with surgical cover.
Paediatric appendicitis & the acute abdomen
Ultrasound is first-line for the child with right-iliac-fossa or acute abdominal pain — it avoids CT radiation and can settle appendicitis, its mimics, and several surgical emergencies. Graded compression is the core skill.
High yield Acute appendicitis
A non-compressible, blind-ending tubular structure with an outer diameter >6 mm and wall thickness >3 mm. Non-compressibility under graded compression is as important as the number.
Target appearance in cross-section (fluid-filled lumen, echogenic mucosa/submucosa, hypoechoic muscularis); an appendicolith casts an acoustic shadow; hyperaemic wall on colour Doppler.
Echogenic (inflamed) periappendiceal fat, free/loculated fluid, prominent local nodes, and — if perforated — a complex collection/abscess and loss of the wall layers.
High-frequency linear over the point of maximal tenderness; graded compression displaces gas; trace the caecal pole to the appendiceal base. A non-visualised appendix does not exclude appendicitis.
Perforation caution: a perforated appendix with surrounding hyperechoic fat can mimic other RUQ/RIF pathology; correlate clinically and consider further imaging if US is equivocal.
Mimic Mesenteric adenitis & intussusception cross-reference
Clusters of enlarged, oval, hypervascular mesenteric nodes (commonly RIF), often with mild bowel-wall thickening and a normal, compressible appendix — the classic self-limiting mimic of appendicitis in children.
Younger children with colicky pain — remember the target/pseudokidney signs (see the Intussusception tab). Always image the RUQ.
Emergency Malrotation & midgut volvulus
Bilious vomiting in a neonate/infant is midgut volvulus until proven otherwise — a surgical emergency threatening the whole midgut. Upper-GI contrast is the traditional gold standard, but US is increasingly used and can be diagnostic.
Colour Doppler shows the superior mesenteric vein and mesentery spiralling clockwise around the SMA — the whirlpool of a volvulus.
Normally the SMV lies to the right of the SMA; an inverted/abnormal SMA–SMV relationship suggests malrotation (supportive, not definitive).
Duodenal obstruction/”double-bubble” configuration, D3 not crossing the midline behind the SMA, and dilated fluid-filled proximal bowel.
Bilious vomiting = emergency. Do not delay surgical referral awaiting perfect imaging; a normal US does not fully exclude malrotation.
Emergency Testicular torsion & the acute scrotum
Time-critical. Colour/spectral Doppler shows absent or markedly reduced intratesticular flow compared with the contralateral testis; the twisted “whirlpool” of the spermatic cord may be seen; the testis becomes swollen and heterogeneous as it infarcts. Torsion is a clinical diagnosis — do not let imaging delay surgical exploration.
Epididymo-orchitis shows increased flow; torsion of a testicular/epididymal appendage shows a focal avascular nodule with preserved testicular flow (“blue dot”).
Do not delay. A high clinical suspicion of torsion warrants immediate exploration regardless of Doppler; early torsion can retain some flow.
Gynae Ovarian pathology in girls
An enlarged, oedematous ovary with peripherally displaced follicles (“string of pearls”), a possible lead cyst/mass, and reduced/absent Doppler flow — though flow may be preserved early because of dual blood supply. Suspect it in a girl with sudden pelvic pain.
Functional cysts are common; look for a lead point for torsion (dermoid, cyst). Correlate with clinical and menarchal status.
Neonatal cranial & spinal ultrasound
The open anterior fontanelle is a natural acoustic window onto the neonatal brain, and the incompletely ossified posterior elements let you image the spinal cord in early infancy — both radiation-free, cot-side and repeatable. These windows close with age (fontanelle ~ 9–18 months; spinal window in the first months of life).
High yield Cranial: what to assess
Anterior fontanelle for coronal and sagittal/parasagittal sweeps; mastoid/posterior fontanelle to see the posterior fossa. Assess ventricles (size/symmetry), germinal matrix (caudothalamic groove), periventricular white matter, midline structures and extra-axial spaces.
Routine screening in preterm infants (typically <32 weeks or <1500 g), commonly a first scan around day 3–7 (peak GMH/IVH onset is in the first 72 h) with follow-up to detect PVL and post-haemorrhagic dilatation.
High yield Germinal matrix / IVH — Papile grading
| Grade | Finding | Severity |
|---|---|---|
| I | Germinal matrix (subependymal) haemorrhage only, at the caudothalamic groove | Mild |
| II | IVH into normal-sized ventricles (fills <50% of ventricle) | Mild |
| III | IVH with ventricular dilatation (fills >50% / distends ventricle) | Severe |
| IV | Periventricular haemorrhagic infarction (venous infarct of adjacent white matter) | Severe |
Grade IV is best understood as periventricular haemorrhagic infarction (medullary-vein congestion from a large matrix clot), not simple “extension” of blood into brain. Grades III–IV carry the greatest risk of post-haemorrhagic hydrocephalus and adverse neurodevelopmental outcome.
Cranial PVL & hydrocephalus
Ischaemic white-matter injury dorsolateral to the ventricles: early periventricular echogenicity (label PVL only if persistent >~14 days) evolving to characteristic periventricular cysts — a strong predictor of cerebral palsy (spastic diplegia).
Progressive ventricular dilatation (often post-haemorrhagic). Serial measurements (ventricular index, anterior-horn width, third-ventricle width) track progression and the need for CSF diversion. Also assess for congenital causes (aqueduct stenosis, Dandy-Walker).
High yield Spinal ultrasound — tethered cord & the sacral dimple
Cutaneous markers of occult spinal dysraphism — sacral dimple (especially high/atypical, >2.5 cm from the anus, or with other stigmata), hair tuft, haemangioma, lipoma, deviated gluteal cleft. Feasible while posterior elements remain cartilaginous (best in the first ~ few months). Prone, high-frequency linear.
The conus medullaris tip normally lies at L1–L2; a tip below L2–L3 is abnormal (low-lying cord) and suggests tethering.
Normally ≤2 mm; a filum >2 mm (thickened/fatty filum) supports a tethered cord.
Normal cord and nerve roots pulsate/oscillate with the cardiac cycle and respiration; reduced or absent motion with a dorsally-fixed cord is a further sign of tethering.
Confirm with MRI: abnormal or equivocal spinal US (low conus, thick filum, mass, absent motion) needs MRI, which is the definitive test for dysraphism.
Paediatric renal tract & other
Antenatally-detected renal pelvis dilatation is a very common referral; postnatal ultrasound characterises it, grades it and directs further work-up (functional and reflux studies). US also detects duplex systems, ureteroceles and neonatal adrenal haemorrhage.
High yield Hydronephrosis — SFU grading
| SFU grade | Ultrasound finding |
|---|---|
| 0 | No hydronephrosis (no pelvic dilatation) |
| 1 | Renal pelvis only visualised/dilated |
| 2 | Dilated pelvis + a few (not all) calyces |
| 3 | Dilated pelvis + virtually all calyces (uniform), normal parenchyma |
| 4 | Grade 3 + parenchymal (cortical) thinning |
Measure the anteroposterior renal-pelvis diameter as an objective adjunct; note that a full bladder and over-hydration exaggerate dilatation — image with a normally-filled bladder and, ideally, not immediately post-void. The newer UTD (urinary-tract-dilation) classification is increasingly used alongside SFU.
Anatomy Duplex system & ureterocele
An enlarged kidney with two separate pelvicalyceal systems. By the Weigert–Meyer rule the upper-pole moiety ureter inserts ectopically/inferomedially (prone to obstruction/ureterocele) and the lower-pole ureter inserts orthotopically (prone to reflux). Look for upper-pole hydronephrosis with a “drooping lily”.
A thin-walled cystic ballooning of the distal ureter within the bladder — image the bladder to catch it (it may inflate and deflate); associated with upper-pole obstruction in a duplex system.
Reflux VUR & contrast-enhanced voiding US (ceVUS)
Vesicoureteric reflux is traditionally assessed by fluoroscopic MCUG (radiation) or a radionuclide cystogram. Grey-scale US is insensitive for reflux, but can raise suspicion (dilated ureter, variable pelvic dilatation, cortical scarring).
Contrast-enhanced voiding urosonography instils ultrasound microbubble contrast into the bladder via a catheter and watches for retrograde bubbles into the ureter/collecting system — a radiation-free alternative to MCUG for detecting and grading reflux, increasingly used in children.
Neonatal Adrenal haemorrhage
A suprarenal mass in a neonate (birth trauma, hypoxia, large size), often right-sided. Typically starts as an echogenic/heterogeneous avascular lesion that evolves over serial scans — shrinking, becoming cystic/anechoic and later calcifying.
The main mimic is neonatal neuroblastoma (may show internal vascularity and does not involute). Serial ultrasound showing progressive resolution favours haemorrhage; a persistent/enlarging or vascular mass needs further work-up.
Pro Paediatric ultrasound — go deeper
The tabs above are the free clinical core. High Yield Pro unlocks the practical, exam-ready layer:
- Step-by-step, image-labelled Graf worksheets with a built-in alpha/beta angle calculator and a IIa-vs-IIb age-decision aid.
- Structured reporting templates for hip, HPS, intussusception, appendix, cranial (with IVH/PVL staging) and renal tract (SFU + UTD).
- Annotated normal-vs-abnormal clip library (target/pseudokidney, whirlpool, absent testicular flow) and a “pitfalls & mimics” bank.
- Paediatric normal-values quick-reference by age, plus enema-reduction and torsion escalation checklists.
- OSCE/viva scenario drills and a paediatric-US question bank.
References & further reading
- Graf R. Fundamentals of sonographic diagnosis of infant hip dysplasia. J Pediatr Orthop; Graf method (alpha ≥60° = Type I). Radiopaedia: Graf method for US classification of DDH.
- The Radiology Assistant. Developmental dysplasia of the hip — ultrasound.
- Radiopaedia. Developmental dysplasia of the hip.
- American Academy of Pediatrics / national screening guidance on DDH and hip ultrasound timing (~6 weeks).
- Hernanz-Schulman M. Infantile hypertrophic pyloric stenosis. Radiology. Radiopaedia: Hypertrophic pyloric stenosis.
- Costa Dias S, et al. Hypertrophic pyloric stenosis: tips and tricks for ultrasound diagnosis. Insights Imaging.
- Said M, et al. Ultrasound measurements in HPS: don’t let the numbers fool you.
- Peck D. Pyloric stenosis (StatPearls). NCBI Bookshelf.
- Radiopaedia. Intussusception (target/pseudokidney; poor-prognosis signs).
- ACEP SonoGuide. Intussusception.
- Applegate KE. Intussusception in children: imaging and reduction. RadioGraphics.
- Sivit CJ. Imaging the child with right lower quadrant pain / appendicitis. RadioGraphics.
- ACEP EM Ultrasound. How to diagnose appendicitis in a child (appendix >6 mm, non-compressible).
- Radiopaedia. Acute appendicitis and intestinal malrotation / midgut volvulus (whirlpool sign).
- Strouse PJ. Malrotation and midgut volvulus in the child. Pediatr Radiol.
- Radiopaedia. Testicular torsion and ovarian torsion.
- Papile LA, et al. Incidence and evolution of subependymal and intraventricular haemorrhage. J Pediatr (Papile IVH grading I–IV). Radiopaedia: germinal matrix / IVH grading.
- Canadian Paediatric Society. Routine imaging of the preterm neonatal brain (screening <32 wks/<1500 g; PVL).
- NHS GGC paediatric guidelines. Routine cranial ultrasound for preterm infants.
- Lowe LH, et al. Neonatal spine sonography. AJR / RadioGraphics (conus L1–L2; abnormal below L2–L3; filum >2 mm). AJR: Sonography of the neonatal spine, part 2.
- Radiopaedia. Tethered spinal cord.
- Fernbach SK, Maizels M, Conway JJ. Ultrasound grading of hydronephrosis: the Society for Fetal Urology (SFU) system. Pediatr Radiol.
- Nguyen HT, et al. Multidisciplinary consensus on urinary tract dilation (UTD) classification. J Pediatr Urol.
- Radiopaedia. Duplex collecting system, ureterocele and contrast-enhanced voiding urosonography (ceVUS).
- Radiopaedia. Neonatal adrenal haemorrhage (vs neuroblastoma).
- Image Gently Alliance. Radiation safety in paediatric imaging (ALARA).
References are for orientation and further reading; some are cited by title where a stable public link is not linked. Always confirm thresholds and pathways against current national guidelines and your local protocol book.