Epiploic Appendagitis & Omental Infarct
- These are two cousins of the same idea: a little blob of abdominal fat loses its blood supply, dies, and gets angry — causing pain that feels like a surgical emergency but almost never is.
- Both are self-limiting. The whole reason you care is to recognize them on CT and stop someone from getting an unnecessary operation.
- Epiploic appendagitis: a small fatty tag hanging off the colon twists or clots off. Look for a tiny (~1–4 cm) oval of fat with a bright rim, usually next to the sigmoid.
- Omental infarct: a bigger chunk of the fatty apron (omentum) dies. Look for a larger swirled mass of inflamed fat, classically on the right side near the ascending colon.
- The signature finding for both is fat that's inflamed but the bowel wall right next to it is fine. That mismatch is your whole diagnosis.
Here's a fun fact that makes the abdomen a lot more interesting: your colon has little decorative fat tassels dangling off it. They're called epiploic appendages, and for most of your life they do approximately nothing. But occasionally one of these tassels twists on its own stalk or clots off its tiny vein, and the fat inside dies. The result is a patient clutching their left lower belly, convinced they have diverticulitis — and a CT that says "relax, it's just a sad fat tag."
Two flavors of fat going bad
Both of these conditions are the same plot: a piece of intra-abdominal fat loses its blood supply, infarcts, and throws an inflammatory tantrum. They mostly differ by which fat and how big.
| Feature | Epiploic appendagitis | Omental infarct |
|---|---|---|
| What dies | A small fat tag off the colon | A chunk of the greater omentum (the fatty apron) |
| Typical size | Small oval, ~1–4 cm | Larger, often >5 cm |
| Classic location | Sigmoid / left lower quadrant | Right side, near ascending colon |
| Classic patient | Adults, often mildly obese | Same, plus kids more than you'd expect |
Notice neither one involves the bowel itself. That's the key to the whole thing.
Why it fakes an emergency
The fat tag dying hurts, and it hurts in a fixed, focal spot — right where the tag is. So someone with left-sided epiploic appendagitis walks in looking exactly like diverticulitis, and someone with a right-sided omental infarct looks exactly like appendicitis. Same neighborhood, same story, completely different treatment. One gets surgery or antibiotics; the other gets ibuprofen and a pat on the shoulder.
This is one of radiology's genuinely satisfying saves. The clinical exam can't tell these apart from their dangerous mimics, but CT can — and the difference is "go home" versus "go to the OR." When you catch one of these, you've earned your salary for the day.
What it looks like on CT
CT is the star here, because the whole diagnosis lives in the fat, and CT is great at fat. Remember that fat is dark on CT — low attenuation, near the bottom of the gray scale. When fat gets inflamed, fluid and inflammatory gunk seep in, and it stops looking clean and black and starts looking hazy and streaky. Radiologists call that fat stranding — picture a clear glass of oil that someone stirred dirt into.
Epiploic appendagitis has a near-pathognomonic look: a small oval of fat sitting right against the colon wall, with a thin bright (hyperattenuating) rim around it — the inflamed lining of the tag. Often there's a tiny dense dot in the center, the "central dot sign," which is the thrombosed little vein at the core. It's like finding the pit in an olive.
Omental infarct is the bigger, messier sibling: a larger, ill-defined mass of fatty tissue with swirled or whorled stranding, classically tucked between the right anterior abdominal wall and the ascending or transverse colon. No bright capsule rim, no central dot — just a sizeable chunk of fat that clearly had a very bad day.
The trap, and how not to fall in it
The mimics are the whole point. Epiploic appendagitis sits next to the sigmoid and screams "diverticulitis"; omental infarct sits near the cecum and screams "appendicitis." The tell that saves you: in these fat conditions the inflammation is centered in the fat, and the adjacent bowel wall is normal — no wall thickening, no obstructed appendix, no diverticula doing the actual inflaming. When the worst-looking thing on the scan is the fat itself and the bowel is innocent, think fat infarct.
You usually don't need follow-up imaging or treatment beyond pain control. These resolve on their own over a few weeks, and a confident CT read lets everyone skip the antibiotics and the operating room. The most valuable thing you can write in the report is a clear statement that the bowel is normal.
The one thing to remember
Both of these are fat that died and got loud about it. Find the inflamed fat, then check the bowel right next to it. If the bowel is calm, you're almost certainly looking at a benign, self-limiting fat infarct — and you've just talked someone out of a surgery they didn't need.