Ureteral Stones & Complications
- A ureteral stone is a tiny rock wedged in a tiny tube, and the imaging test of choice is a non-contrast CT of the abdomen and pelvis ("CT KUB").
- Almost all stones are dense (white) on CT — even uric acid stones, the ones famous for being invisible on a plain X-ray, still show up on CT.
- Don't just find the stone — describe its size and location, because those two facts drive whether it passes on its own or needs a urologist.
- The real diagnosis is often the consequence: a dilated collecting system (hydronephrosis) and fat stranding around the kidney and ureter. These "secondary signs" tell you the stone actually matters.
- The scary complication is an obstructed, infected system — that's a urologic emergency, not a "drink water and wait" situation.
Imagine the world's worst pebble in the world's narrowest garden hose, except the hose is inside you and it really, really wants you to know about it. That's a ureteral stone. People describe the pain as worse than childbirth, which is a bold claim from a stone roughly the size of a sesame seed. Our job on imaging is calmer: find the rock, measure it, and figure out how angry the kidney upstream is about the traffic jam.
Why CT, and why no contrast
The go-to study is a non-contrast CT of the abdomen and pelvis, often called a CT KUB (kidneys, ureters, bladder). The trick is that stones are dense — they soak up X-rays like little chunks of bone — so they show up bright white against the darker soft tissue and fat around them. Adding IV contrast would be like turning on every light in the room when you're trying to spot a single firefly: the contrast lights up the kidneys and ureters white too, and your white stone vanishes into the glare. So we deliberately leave the lights off.
Nearly all stones are visible on CT, including uric acid stones. That surprises people, because uric acid stones are the classic "radiolucent" stones that hide on a plain abdominal X-ray. CT sees density directly, so it catches them anyway. The plain-film blind spot doesn't apply here.
Ultrasound is the other player, especially when you want to avoid radiation — pregnant patients, kids, or someone who's had ten of these CTs already. It's great at showing a swollen kidney and can catch stones at the very top (near the kidney) and very bottom (near the bladder), but the long middle stretch of ureter is hidden behind bowel gas, so it misses stones in that no-man's-land.
Finding the stone (and proving it's the culprit)
Spotting a bright dot is the easy part. The harder, more useful skill is reporting the two things the urologist actually acts on:
- Size — measured on CT. Small stones tend to pass on their own; larger ones are far less likely to, and are more likely to need a procedure.
- Location — stones love to lodge at the three natural pinch-points where the ureter is narrowest: where the kidney funnels into the ureter (the ureteropelvic junction), where the ureter crosses over the pelvic blood vessels, and where it tunnels into the bladder (the ureterovesical junction). That last one is the most common place to get stuck — it's the off-ramp with the worst congestion.
But here's the part beginners skip. A stone with no consequences is almost suspicious — did it really cause this pain? So we hunt for the secondary signs that prove the stone is obstructing:
- Hydronephrosis — the collecting system inside the kidney balloons up with backed-up urine. (This earns its own deep dive in hydronephrosis and obstruction.)
- Hydroureter — the ureter above the stone is dilated, like a hose that's swollen behind a kink.
- Perinephric and periureteric fat stranding — the normally crisp, black fat around the kidney and ureter gets hazy and dirty-looking, the imaging version of swelling and irritation.
The "soft signs" can clinch the diagnosis when the stone itself is tiny or already passing. An asymmetrically enlarged, edematous kidney with stranding on one side — even with only a whisper of a stone — tells you which side hurts and that the obstruction is real and recent.
When a stone becomes an emergency
Most stones are a painful inconvenience that pass with time and fluids. The version that gets people into trouble is an obstructed system that becomes infected — urine trapped behind a stone is a warm, stagnant pond, and bacteria throw a party. A blocked, infected kidney (pyonephrosis) can tip someone into sepsis fast.
An obstructing stone plus signs of infection (fever, pus, a sick patient) is a urologic emergency. The pressure has to come off the kidney — typically by draining it — and that can't wait for the stone to pass on its own. On imaging, worry when an obstructed kidney also shows debris in a dilated system or surrounding inflammation in a febrile patient.
A phlebolith — a small calcified clot in a pelvic vein — looks almost exactly like a ureteral stone: a tiny white dot in the pelvis. The classic tell is the soft-tissue rim sign, where a true ureteral stone is wrapped in a thin rim of the swollen ureter wall, while phleboliths often have a little comet tail of vessel trailing off them. When stuck, trace the ureter: a real stone sits in the ureter and has dilation above it.
The one-line takeaway
Find the bright stone on the non-contrast CT, measure it, locate it at one of the pinch-points — but spend equal energy on the upstream story. Hydronephrosis, hydroureter, and fat stranding turn "there's a stone" into "there's an obstructing stone," and the moment infection joins that picture, the clock starts ticking.