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Abdominal and urinary tract imaging in children

Bilious vomiting in a newborn is malrotation with volvulus until proven otherwise (urgent upper GI study), intussusception is diagnosed by US and reduced by enema, pyloric stenosis is measured on US, and in an abdominal mass Wilms tumour is separated from neuroblastoma by origin and calcification.

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Why it matters in the exam

Malrotation with volvulus: a newborn with bilious vomiting — an emergency. The test: an upper GI contrast study — the duodenojejunal (DJ) flexure is not to the left of the spine at the level of the duodenal bulb, and in volvulus the duodenum looks like a "corkscrew". On US: the SMV is positioned left of the SMA, and there is a whirlpool sign. Duodenal atresia — "double bubble", associated with Down syndrome. Hirschsprung disease: delayed passage of meconium; on enema — a reversed rectosigmoid ratio (less than 1) and a transition zone; the diagnosis is by biopsy. Meconium ileus (cystic fibrosis) — a microcolon and "soap bubbles" in the right lower quadrant. NEC in a preterm infant: pneumatosis intestinalis, portal gas, and free air that requires surgery.

Intussusception: age 3 months to 3 years, usually ileocolic; on US a "target" or "doughnut" in cross-section. Treatment: reduction by air or fluid enema under fluoroscopy or US; contraindications — peritonitis, free air or shock. Pyloric stenosis: age 2–8 weeks, non-bilious projectile vomiting; on US muscle thickness 3 mm or more and channel length 15 mm or more. Appendicitis in a child — US first. Neonatal jaundice lasting more than two weeks — exclude biliary atresia: on US a small or absent gallbladder and the "triangular cord" sign; on HIDA no excretion into the bowel even after 24 hours.

Abdominal mass: Wilms tumour — age 3–4, arising from the kidney (the "claw sign"), displacing vessels, spreading to the vena cava and lungs, and calcifying only rarely; neuroblastoma — a younger age, from the adrenal, calcified in most cases, encasing vessels, crossing the midline and metastasising to bone. Urinary tract: renal pelvic dilatation from pregnancy — US 48–72 hours after birth (earlier, physiological dehydration hides dilatation), unless there is severe bilateral dilatation or a boy with suspected posterior urethral valves (PUV) — then early US and VCUG. PUV: a boy, a dilated posterior urethra ("keyhole"), a thick bladder and bilateral hydronephrosis. After a first febrile UTI at age 2–24 months — renal and bladder US; VCUG only if US is abnormal or the infection recurs. DMSA shows scars. In the newborn kidney the cortex is echogenic and the pyramids prominent and hypoechoic — normal.

Key points

• Bilious vomiting — urgent upper GI study.
• Intussusception — US and target; enema reduction.
• Pylorus — 3 mm and 15 mm.
• Wilms versus neuroblastoma — kidney versus adrenal and calcifications.
• Renal pelvic dilatation — US after 48–72 hours.

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Sources

• AAP Clinical Practice Guideline: Urinary Tract Infection in Febrile Infants and Children 2–24 Months, 2011, reaffirmed 2016 — Imaging after the first febrile UTI
• ESPR Abdominal Imaging Task Force: Imaging of intussusception and reduction, 2021 — US diagnosis and enema reduction
• Society for Fetal Urology / UTD Classification System, 2014 — Postnatal management of urinary tract dilation

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.