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Suspected ureteric calculus in an adolescent with non-diagnostic ultrasound — MSRA MCQ

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HardNephrolithiasisSuspected ureteric calculus in an adolescent with non-diagnostic ultrasoundMSRA

A 15-year-old boy presents to an urgent treatment centre with 10 hours of sudden, severe left-sided colicky flank pain radiating to the groin and vomiting. He is afebrile and haemodynamically stable. Urine dipstick is positive for blood but negative for nitrites and leucocytes; creatinine is normal. Urgent renal tract ultrasound shows mild left hydronephrosis but does not identify a renal or ureteric calculus. His pain remains typical of renal colic, and no alternative diagnosis has been established. What is the most appropriate next imaging investigation?

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Correct answer: D — Low-dose non-contrast CT of the kidneys, ureters and bladder

This patient is under 16 years, so ultrasound is the appropriate first-line investigation for suspected renal colic, rather than immediate CT. However, the ultrasound has not demonstrated a calculus and the diagnosis remains uncertain despite persistent symptoms strongly suggestive of ureteric obstruction. NICE advises considering low-dose non-contrast CT when uncertainty about renal colic remains after ultrasound in children and young people. A repeat ultrasound may eventually demonstrate evolving dilatation or a migrating stone, but it delays definitive diagnostic clarification when the initial scan is non-diagnostic. A plain KUB radiograph has limited sensitivity, misses radiolucent stones and does not adequately assess alternative pathology. Contrast-enhanced CT urography is not the appropriate CT protocol for stone detection and adds contrast exposure without improving first-line stone assessment. Magnetic resonance urography avoids ionising radiation but is not the recommended escalation test for suspected calculi after non-diagnostic ultrasound. Low-dose non-contrast CT KUB provides the appropriate balance of diagnostic accuracy and radiation minimisation in this specific escalation scenario.

Reference: Renal and ureteric stones: assessment and management (NG118) — Recommendations (2019; updated 2026) — https://www.nice.org.uk/guidance/ng118/chapter/Recommendations