Disproportionate haematuria after minor trauma often reveals a pre-existing renal abnormality — PUJ obstruction, Wilms tumour, horseshoe kidney — so the scan reports the underlying kidney, not only the injury.
Orient first
- Hydronephrotic and ectopic kidneys are injured by forces that spare a normal kidney.
- Ultrasound triages; CT is reserved for haemodynamic change or suspected significant injury (verify the local paediatric trauma pathway).
- A mass found this way is staged as a tumour, not graded as trauma.
Acquire the study
- Curvilinear probe over both kidneys and the bladder, colour Doppler of the renal hila.
The manoeuvre
- Each kidney: length in cm for age, pelvicalyceal dilatation (APRPD in mm), position and fusion.
- Mass: solid, heterogeneous, arising from the kidney (claw sign).
- Perirenal fluid or haematoma.
- Colour Doppler: renal vein and IVC patency.
What confirms it
- Injury graded, and an underlying anomaly named when present.
What licenses you to exclude it
- A normal ultrasound of both kidneys in a stable child makes significant injury unlikely.
The classic misread
- Grading a ruptured hydronephrosis as a simple laceration.
- Missing a Wilms tumour presenting after a fall.