Urothelial Cancer & CT Urography

Think of the inside of your urinary tract as one continuous tube wallpapered with a single sheet of living tissue called the urothelium. It lines the renal pelvis, snakes down both ureters, and balloons out to cover the bladder. Urothelial cancer is when that wallpaper goes bad, and because it's all the same wallpaper, a problem in one patch is a warning to check every other patch. That single idea is the whole reason imaging for this disease looks the way it does.

Why it shows up everywhere

Most urothelial cancer lives in the bladder, simply because that's where most of the urothelium is (the bladder story, and the MRI scoring system built for it, lives at bladder cancer and VI-RADS). But it can also grow up in the ureters or renal pelvis (the funnel where the kidney drains), where it is called upper tract urothelial carcinoma (UTUC). Here's the catch that trips people up: these tumors love company. A patient can have one in the bladder and one in a ureter at the same time, or develop a new one later somewhere else along the tract. Radiologists describe this as a "field" problem: the whole lining shares the same risk, so the whole lining gets the same scrutiny.

This is exactly why you can't just scan the bladder and call it a day. You have to follow the wallpaper all the way up.

Painless blood is the alarm bell

The symptom that usually starts the whole workup is hematuria, blood in the urine, and the unsettling part is that it's often painless and visible. No burning, no pain, just an alarming color one morning. That lack of drama is precisely why it's taken seriously: painless visible hematuria in an adult is a "rule out tumor until proven otherwise" situation, not a "wait and see" one. The standard workup pairs cystoscopy (a camera in the bladder, which imaging cannot replace) with CT urography for everything above it.

Findings by modality

CT urography

The go-to study is CT urography (CTU): a CT engineered around one trick, timing. You give intravenous iodinated contrast and then image at more than one moment, because the tract is interesting at different times. Think of pouring cream into coffee. Early, it's a bright swirl in the cup (contrast lighting up the kidney tissue and any tumor). Later, it's mixed and settled into the liquid filling the cup (contrast excreted into the urine, now filling the collecting system and ureters). CTU catches both moments.

The European Society of Urogenital Radiology (ESUR) guideline allows two ways of getting there: either a single combined nephrographic–excretory phase after a split-bolus injection (two smaller injections separated in time, so the kidney is enhancing and excreting on one scan), or separate nephrographic and excretory phases after a single bolus. The split-bolus route saves dose; the two-phase route gives a cleaner look at the parenchyma. The full recipe, timing, and tricks are on the CT and MR urography protocols page.

On the images, a urothelial tumor has two main looks. Either a filling defect sitting in the lumen on the excretory phase, a dark hole in the bright contrast like a pebble interrupting a stream of white paint, or focal, often irregular wall thickening of the renal pelvis, an infundibulum, or the ureter, best appreciated on the nephrographic phase where it enhances. In the ureter a tumor can also cause upstream obstruction, so you may see a dilated collecting system above it, the backed-up plumbing pointing you toward the blockage. A slowly growing ureteral tumor can even stretch the ureter just below it into a cup shape, which is the opposite of what a stone does, since a stone leaves the ureter below it collapsed.

Figure · CT

MR urography

MR urography is the radiation-free alternative, useful in younger patients, in pregnancy, and when iodinated contrast is off the table. Heavily T2-weighted images show the urine-filled tract as a bright water map (and are the part relied on in pregnancy, where gadolinium is generally avoided), and gadolinium-enhanced excretory images do what the CTU excretory phase does. It shows enhancing wall thickening and filling defects well; its weak spots are small lesions and stones, which are signal voids and easy to lose.

Ultrasound

Ultrasound is not a screening tool for urothelial tumors, but it is often the first study a patient with hematuria gets, so know what it can show: a soft-tissue mass in the renal pelvis or a hydronephrotic system with a solid, vascular focus at the level of obstruction. Most of the ureter is invisible behind bowel gas.

Retrograde pyelography

When CTU is equivocal or the kidney excretes poorly, the urologist injects contrast directly up the ureter under fluoroscopy. It gives the crispest picture of a ureteral filling defect and the cup-shaped ureter beneath a tumor, and it is usually combined with ureteroscopy and biopsy, which gets the tissue answer.

The numbers

The figures in the table are for the upper tract. There is no equivalent single accuracy figure for CTU in the bladder to quote here, and in practice cystoscopy remains the standard for the bladder itself, which is why hematuria workup uses both.

How good is the test

For upper tract urothelial carcinoma in patients presenting with hematuria, a systematic review and meta-analysis put CT urography's pooled sensitivity at 96% (95% CI 88–100%) and pooled specificity at 99% (95% CI 98–100%). Those are excellent numbers, and they mean two things in practice. A clean, well-opacified CTU is strong reassurance that the upper tracts are clear. And when the CTU shows an enhancing filling defect, it is usually right, so the report should say "urothelial tumor" plainly rather than hedging.

The same numbers cannot be borrowed for MR urography, ultrasound, or for bladder lesions; no robust pooled figure exists for those, so I will say only that they are less sensitive than CTU for the upper tract.

Classification

For the bladder component, multiparametric MRI is scored with VI-RADS, which estimates the likelihood that a bladder tumor has invaded the muscle layer. The abbreviated version is below; the full criteria, the sequence-by-sequence rules, and worked examples are on the VI-RADS classification page. There is no equivalent named imaging system for the upper tract.

VI-RADS 2018, abbreviated.

What could it be instead

Two things wear the same costume as a urothelial tumor: a filling defect that isn't tumor, and wall thickening that isn't tumor. The single most useful feature for sorting them out is enhancement, because tumor has its own blood supply and clot and stone do not.

Urothelial cancer arises from the lining of the tract, which makes it a different beast from a renal mass, which grows out of the kidney's own substance and bulges the contour rather than sitting in the urine-filled space. And while a stone, the bread and butter of renal colic imaging, can cause hematuria and a filling defect too, it announces itself on the unenhanced phase by being bright and dense. Keeping these three straight is most of the day-to-day diagnostic work.

Figure · CT

Reporting

• Where: renal pelvis, infundibulum or calyx, proximal, mid or distal ureter, bladder, and which side; whether it is single or multifocal.
• What it looks like: filling defect versus wall thickening, size, and, crucially, whether it enhances on the nephrographic phase.
• Obstruction: hydronephrosis or hydroureter above it and its severity.
• Local extent: extension into the renal sinus fat or parenchyma, periureteral fat stranding or mass, and the relation to adjacent organs.
• The rest of the tract: a deliberate statement that the contralateral collecting system, the other ureter, and the bladder have been surveyed, and any additional lesions.
• Spread: retroperitoneal and pelvic lymph nodes, the liver, lungs on the included images, and bone.
• Technical caveats: any segment of ureter that was not opacified on the excretory phase, because an unopacified segment is an unexamined segment.

When painless visible hematuria walks in, picture that single continuous sheet of wallpaper. Get a CT urogram, use the unenhanced phase to dismiss stones, the nephrographic phase to find enhancing soft tissue, and the excretory phase to silhouette filling defects in bright urine. And never stop at the first lesion. This is a disease that likes to show up in more than one place at once.

References

• Chlapoutakis K, Theocharopoulos N, Yarmenitis S, Damilakis J. Performance of computed tomographic urography in diagnosis of upper urinary tract urothelial carcinoma, in patients presenting with hematuria: Systematic review and meta-analysis. Eur J Radiol 2010;73(2):334–338. Used for: the pooled sensitivity of 96% (95% CI 88–100%) and pooled specificity of 99% (95% CI 98–100%) of CT urography for upper tract urothelial carcinoma in patients with hematuria, in Key Points, "The numbers", and "How good is the test".
• Van Der Molen AJ, Cowan NC, Mueller-Lisse UG, Nolte-Ernsting CC, Takahashi S, Cohan RH; CT Urography Working Group of the European Society of Urogenital Radiology (ESUR). CT urography: definition, indications and techniques. A guideline for clinical practice. Eur Radiol 2008;18(1):4–17. Used for: the split-bolus combined nephrographic–excretory versus single-bolus two-phase strategies in "Findings by modality" and "The numbers", and the CTDIvol dose bands (5–6 mGy benign, 9–12 mGy potential malignant disease, 2–3 mGy optional unenhanced series) in "The numbers".
• Panebianco V, Narumi Y, Altun E, et al. Multiparametric Magnetic Resonance Imaging for Bladder Cancer: Development of VI-RADS (Vesical Imaging-Reporting And Data System). Eur Urol 2018;74(3):294–306. Used for: the abbreviated VI-RADS 1 to 5 category definitions, including the 1 cm size cut, in "Classification".