Paediatric Radiology
Neonatal chest
Hyaline membrane disease: low lung volumes, diffuse ground glass, air bronchograms in a preterm infant. Transient tachypnoea of the newborn: normal to increased volumes, perihilar streaking and fluid in fissures, resolving within days. Meconium aspiration: patchy asymmetric consolidation with hyperinflation, usually at term. Air leak: pneumothorax, or pneumomediastinum with the spinnaker sail sign.
Gastrointestinal
Intussusception: ultrasound doughnut or target sign, pseudokidney on plain film; air or contrast enema is diagnostic and therapeutic unless there is perforation or peritonitis. Pyloric stenosis: thickened muscle of 3 mm or more and canal length of 15 mm or more. Malrotation with volvulus: abnormal SMA/SMV relationship, whirlpool sign and proximal duodenal obstruction. Necrotising enterocolitis: pneumatosis, portal venous gas, fixed loops. Hirschsprung disease: delayed meconium and a transition zone on contrast enema.
Musculoskeletal
Developmental dysplasia of the hip is assessed by ultrasound before ossification, using the Graf classification. Slipped upper femoral epiphysis: widened physis, Klein line failing to intersect the femoral head, typically in obese adolescents. Recognise toddler's fracture and the patterns of non-accidental injury: metaphyseal corner fractures, posterior rib fractures, injuries of differing ages.
Traps
The normal thymus (sail and wave signs) mimics a mediastinal mass. Physiological periostitis of the newborn is normal. Radiation protection matters: use ultrasound first and avoid unnecessary repeat imaging.
Rule of thumb
Pyloric muscle thickness of 3 mm or more with a canal length of 15 mm or more is highly accurate for hypertrophic pyloric stenosis.