Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Select renal imaging by the clinical question, recognise modality limitations and escalate obstructed infection, stones, masses and contrast-related risk without delaying necessary diagnosis.
Renal imaging is a sequence of decisions rather than a hierarchy in which CT is automatically superior. Ultrasound rapidly answers structural and drainage questions without radiation or nephrotoxic contrast. CT provides greater spatial detail and can identify ureteric calculi, haemorrhage, trauma, gas, masses and surrounding pathology. MRI offers selected soft-tissue and vascular characterisation, while nuclear medicine measures physiology that conventional cross-sectional imaging cannot directly quantify.
The principal safety error is a mismatch between urgency and modality. Waiting for routine ultrasound in septic obstruction delays source control; requesting contrast CT for uncomplicated stone detection adds a drug exposure without the intended benefit; ordering non-contrast CT for a suspected enhancing mass may leave the question unanswered. State the suspected diagnosis, side, renal function, pregnancy possibility, relevant operation and exact desired information on the request.
Reports require translation into action. Mild pelvic fullness may reflect a full bladder rather than clinically important obstruction, and severe-looking chronic hydronephrosis may be stable. Conversely, obstruction can exist without dilatation early in its course, with retroperitoneal disease or in profound dehydration. Discordance between a concerning phenotype and apparently reassuring imaging should trigger radiology or urology discussion, not automatic closure.
Fever or hypothermia, rigors, flank pain, pyuria and AKI with hydronephrosis suggest pyonephrosis or an infected obstructed kidney. Antibiotics do not penetrate or drain a pressurised system reliably; decompression is source control.
Sudden severe loin-to-groin pain, restlessness, nausea and haematuria supports ureteric calculus, but aortic, ovarian, testicular, gastrointestinal and musculoskeletal emergencies remain alternatives. Pain severity does not predict stone size or kidney function.
Hesitancy, weak stream, incomplete emptying, suprapubic discomfort, overflow incontinence or a catheter that has stopped draining points toward retention. A bedside bladder scan can redirect the pathway before formal upper-tract imaging.
Incidental solid lesions, enhancement, septation, nodularity or a mass found during haematuria work-up needs protocolled characterisation and urological ownership. A simple cyst has a different pathway from an indeterminate complex lesion.
Small echogenic kidneys, cortical thinning, scarring, asymmetry or multiple cysts can support a chronic process. Normal-sized kidneys do not exclude CKD, and morphology alone cannot quantify reversible activity.
Sudden flank pain with haematuria, embolic risk, severe hypertension, recent instrumentation or significant trauma can indicate infarction, arterial injury or collecting-system disruption and usually needs urgent contrast-enhanced specialist imaging.
Check current AKI or renal function, hydration, prior hypersensitivity and relevant interacting treatment under local radiology policy. Do not withhold a time-critical diagnostic scan reflexively; discuss risk mitigation and alternatives.
Volume depletion, hypotension, poor renal function, bladder distension and protocol timing can distort the curve. This diagnostic use is not treatment of an acutely obstructed infected kidney.
Advanced CKD, AKI, pregnancy and previous reaction require individual radiology assessment. Risk differs between agents, so a generic class instruction is unsafe.
A compliant collecting system may remain wide after a blockage resolves, while an early acute blockage may not yet be visibly dilated. Function, timing and symptoms decide significance.
A CT KUB, portal-venous abdominal CT, renal mass CT and CT urogram acquire different phases. Supplying the clinical question prevents a technically adequate but diagnostically inadequate scan.
Ultrasound can show two unequal kidneys but cannot quantify each kidney's contribution. MAG3 or DMSA can supply relative function for selected surgical and congenital decisions.
Glomerulonephritis, early diabetic kidney disease and drug-related interstitial injury often have no specific structural abnormality. Urine, serology and sometimes biopsy answer those questions.
The relevant comparison is the renal and systemic risk of the proposed agent against the harm of missed pulmonary embolism, infarction, abscess, trauma or malignancy and the value of a non-contrast alternative.
A radiology recommendation is not a follow-up system. Explicit ownership prevents an indeterminate renal lesion from disappearing between acute and primary care.
Equating hydronephrosis with definite active obstruction without clinical or functional correlation.
Using a normal ultrasound to dismiss ongoing anuria or high clinical suspicion of retroperitoneal obstruction.
Ordering a contrast CT urogram for straightforward calculus detection when low-dose non-contrast CT is the intended adult test.
Delaying drainage of an infected obstructed kidney while waiting for antibiotic response.
Describing every small echogenic kidney as irreversible without checking prior imaging and the treatable clinical phenotype.
Treating a nuclear drainage half-time as self-interpreting despite poor function, dehydration or a full bladder.
Failing to assign responsibility for a complex cyst or renal mass found incidentally.
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An adult has fever, flank pain, acute kidney injury and a history of ureteric stones. Pyonephrosis is suspected. Which imaging approach best matches NICE guidance?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes