Renal Infarct & Vascular Disease
- A renal infarct is a piece of kidney that lost its blood supply — on contrast CT it shows up as a sharply outlined wedge that simply doesn't light up while the rest of the kidney does.
- The classic shape is a wedge pointing inward toward the hilum, because the renal arteries branch like a fan and each branch feeds a triangular slice.
- A thin rim of cortex along the outer edge can still enhance (the "cortical rim sign") because the capsule gets a trickle of blood from other vessels — a late, helpful clue.
- The usual culprit is an embolus (often from the heart, e.g. atrial fibrillation) or in-situ trouble like dissection, vasculitis, or trauma.
- The big mimics are pyelonephritis and a hypovascular tumor — context and shape usually break the tie.
Think of the kidney as a city that runs entirely on one set of power lines. The renal artery comes in, splits into branches, and each branch lights up its own neighborhood. Cut one line and that neighborhood goes dark — the lights don't flicker, they just stop. A renal infarct is exactly that: a blackout in a slice of kidney, drawn with surprisingly crisp borders because the plumbing is built like a fan.
That fan shape is the whole reason infarcts look the way they do, so let's start there.
Why infarcts are wedge-shaped
The renal artery doesn't supply the kidney as one big soggy sponge. It branches into segmental arteries, and — here's the important part — these are end arteries with essentially no backup connections between them. Each one owns its territory outright, like food courts that refuse to share fries. Block one branch and the slice it feeds dies cleanly, with no neighboring vessel sneaking in to rescue it.
Because that territory is a cone of tissue with its tip at the hilum (where the artery enters) and its base at the outer cortex, the dead zone shows up as a wedge — narrow toward the center, wide toward the surface.
What you actually see on imaging
The diagnosis basically requires contrast. On a non-contrast scan an acute infarct can look completely normal — you can't tell which neighborhood lost power until you turn the lights on. The fix is intravenous iodinated contrast, which depends on how that material soaks into perfused tissue (the physics of that brightness lives in attenuation and radiographic contrast).
After contrast, the infarcted wedge stays dark while everything around it glows. A couple of details earn their keep:
- Sharp, geographic borders. Infarcts have clean edges. Smudgy, ill-defined dark areas point you elsewhere.
- The cortical rim sign. A thin outer ribbon of cortex may still enhance even though the wedge behind it is dead. This is because the renal capsule gets a side-channel blood supply from capsular vessels that don't run through the blocked branch. It's a late finding — it takes hours to days to develop — so a fresh infarct won't have it yet. Don't expect it on the patient who got their CT an hour after symptoms started.
A "global" infarct — the whole kidney out, not just a wedge — usually means the main renal artery itself is occluded (a big embolus, a dissection flap, or a clamped-off pedicle after trauma). The entire kidney fails to enhance, sometimes with that same rim sign hugging the outside.
The company infarcts keep: other renal vascular disease
Infarcts are one chapter of a larger book about renal blood flow. A few neighbors worth knowing:
| Entity | What's happening | Imaging tell |
|---|---|---|
| Embolic infarct | Clot travels from elsewhere (heart, aorta) and plugs a branch | Wedge defect; hunt for a cardiac or aortic source |
| Renal artery dissection | A tear sends blood into the artery wall | Intimal flap; downstream wedge or global infarct |
| Renal vein thrombosis | The drain clots, not the supply | Swollen kidney, delayed/persistent enhancement, clot in the vein |
| Renal artery stenosis | Chronic narrowing, not full blockage | Small kidney, secondary hypertension — see below |
| Vasculitis | Inflamed small vessels | Multiple small peripheral infarcts, sometimes microaneurysms |
Note that renal vein thrombosis flips the story: it's a backed-up drain, not a cut supply, so the kidney gets engorged and swollen rather than shrinking, and contrast lingers instead of failing to arrive.
For the chronic, blood-pressure-driven flavor of vascular disease, the dedicated page on renal artery stenosis is the place to go — that's a slow squeeze with a whole different clinical story, not an acute blackout.
The mimics that will get you
Two impostors love to dress up as infarcts.
Pyelonephritis can also produce wedge-shaped areas of reduced enhancement. The difference is texture and edges: infarcts are sharply demarcated and truly dark, while infected zones tend to be striated (a streaky "stripey" pattern radiating outward) and the patient is usually febrile with pyuria. When you see stripes plus a sick, feverish patient, think infection — start with the renal infection spectrum.
The other trap is a hypovascular tumor. A poorly enhancing mass can look like a dark patch too — but masses are usually rounded and bulge or distort the contour, whereas an infarct respects the kidney's shape and follows that vascular-territory wedge. When something looks mass-like rather than territorial, detour through RCC subtypes and staging.
Found a clean renal infarct with no trauma? Your next question is "where did the clot come from?" An unexplained infarct is often the kidney quietly reporting a heart problem — atrial fibrillation is a classic source — so the workup frequently points back at the chest, not the abdomen.
The one thing to carry out
If you remember nothing else: a renal infarct is a sharply defined, wedge-shaped slice of kidney that won't take up contrast, pointing toward the hilum, sometimes with a rescued rim of cortex on its outer edge. Find that shape, then go looking for the embolus, the dissection, or — in the right setting — the trauma that turned off the lights.