CT urography (CTU) is a contrast-enhanced CT designed to assess the kidneys and the lining of the urinary tract, especially in patients with blood in the urine or suspected urothelial disease. A report may describe renal masses, stones, urinary tract dilatation, ureteric narrowing, filling defects and bladder abnormalities. The word “filling defect” does not automatically mean cancer: clots, stones, inflammation and technical factors can mimic a lesion. Suspicious findings usually require review of the images and, depending on location, cystoscopy or ureteroscopy/biopsy.

How CT urography differs from CT KUB

CT KUB is usually non-contrast and optimised for stones. CT urography uses intravenous iodinated contrast and delayed/excretory images so the urine becomes opacified. This allows the radiologist to inspect both the kidney tissue and the inner lining of the collecting system and ureters.

Common phases on the scan

• Non-contrast phase: useful for stones and baseline density.
• Nephrographic phase: shows renal parenchyma and helps characterise masses.
• Excretory/delayed phase: contrast appears in the collecting systems and ureters, allowing assessment for narrowing or filling defects.

Important report terms

Filling defect

A filling defect is an area where contrast does not fill the urinary tract normally. A persistent irregular soft-tissue filling defect may be suspicious for urothelial tumour, but blood clot, sloughed tissue, stone or poor distension can produce a similar appearance.

Urothelial thickening or enhancement

The lining of the renal pelvis or ureter may appear thickened or enhanced in infection, inflammation or tumour. Focal irregular thickening is generally more concerning than smooth diffuse thickening, but imaging alone may not provide tissue diagnosis.

Delayed nephrogram or delayed excretion

A kidney that enhances or excretes contrast more slowly may be obstructed or functionally impaired. The cause should be correlated with ureteric calibre, stones, strictures, masses and creatinine.

Renal mass

Solid or complex renal masses are described by size, enhancement, location and relation to vessels/collecting system. Further MRI, surveillance or treatment may be recommended depending on the appearance and patient factors.

Contrast and kidney function

Iodinated contrast is generally safe when appropriately selected, but clinicians consider kidney function, previous contrast reaction, dehydration and other risk factors. A creatinine/eGFR may be checked before the scan. A history of “iodine allergy” is not interpreted literally; what matters is a previous reaction to iodinated contrast and its severity.

What happens after an abnormal CTU?

Visible bladder lesions are usually assessed with cystoscopy because CT cannot replace direct inspection. Suspicious ureteric or renal-pelvis lesions may require ureteroscopy, urine cytology and biopsy. A renal mass may need dedicated renal imaging. Obstruction may require treatment depending on kidney function, symptoms and infection risk.

How to read the “Impression” section

Start with the final impression, then go back to the body of the report to see the exact site and size of the abnormality. For haematuria work-up, note whether both kidneys enhance symmetrically, whether every ureteric segment is adequately opacified, whether a filling defect or focal thickening is persistent, and whether the bladder was adequately distended. A report may recommend cystoscopy even when CT shows no bladder mass because flat or small mucosal lesions can escape cross-sectional imaging.

If the report says an indeterminate lesion needs “clinical correlation,” “short-interval follow-up” or “dedicated MRI,” that is not a diagnosis. It is a request to answer a more focused question with the appropriate next test.

How to separate an important CTU finding from a technical one

Not every unopacified ureteric segment is a blockage. Ureteric peristalsis, timing of the excretory phase and incomplete distension can create short segments that do not fill with contrast. A suspicious segment becomes more important when there is a matching soft-tissue lesion, focal wall thickening, upstream dilatation or persistent abnormality on additional images.

Likewise, a ‘filling defect’ is a radiological description rather than a diagnosis. Blood clot, sloughed material, a stone and urothelial tumour can all alter the contrast column. The correct next step may be cystoscopy, urine cytology, ureteroscopy or interval imaging depending on the site and clinical reason for the scan.

What to bring for consultation

• CTU images and written report.
• Urine routine/culture and urine cytology if done.
• Serum creatinine/eGFR.
• Previous ultrasound, CT or cystoscopy reports.
• Any biopsy/HPE report and current medicines, especially anticoagulants.

FAQs

Related reading

• CT KUB Report Explained
• Serum Creatinine Test Explained
• HPE / Biopsy Report Explained
• Cancer Staging Report Explained
• Urologist in Latur

References

• RadiologyInfo.org (ACR/RSNA). Urography. Last reviewed March 11, 2024 https://www.radiologyinfo.org/en/info/urography
• European Association of Urology. EAU Guidelines on Urological Infections. 2026 https://uroweb.org/guidelines/urological-infections
• National Cancer Institute. Surgical Pathology Reports https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/pathology-reports-fact-sheet