Bowel & Mesenteric Injury
- Bowel and mesenteric injury is the sneaky one — it hides while the flashy solid-organ injuries grab all the attention.
- The hard sign is full-thickness bowel wall disruption with leaking contents: free air not explained by anything else, and free fluid with nowhere it should be coming from.
- The mesentery can bleed and tear too; watch for active contrast extravasation and a triangle of fluid wedged between bowel loops.
- Most of the findings are soft and easy to talk yourself out of, so when several pile up together, take them seriously — a missed perforation gets worse by the hour.
When someone takes a handlebar to the abdomen or gets folded over a seatbelt, everyone immediately starts hunting for a torn liver or a shattered spleen — the dramatic, bleeding solid organs. Meanwhile the bowel sits there quietly, possibly with a hole punched in it, possibly slowly strangling on its own blood supply, waiting to be overlooked. Bowel and mesenteric injury is the introvert at the trauma party. It rarely announces itself, and it punishes you for not paying attention.
Why the bowel is so easy to miss
Here's the problem. A lacerated spleen pours out blood you can see. A perforated bowel leaks a thimble of fluid and a few bubbles of gas, and those bubbles look an awful lot like the normal gas already living in every loop of intestine. You're trying to spot a specific leak inside a building that is, by design, full of pipes carrying that exact fluid.
So instead of one obvious sign, you collect a handful of soft ones and ask whether the story holds together. No single finding is the magic bullet — but when three or four of them show up in the same neighborhood, the picture sharpens fast.
The findings that matter
The CT signs of bowel and mesenteric injury sort roughly into "the wall itself is hurt" and "stuff is leaking out where it shouldn't be."
| Finding | What it means | Why it's tricky |
|---|---|---|
| Bowel wall discontinuity | A frank hole — full-thickness disruption | Often subtle; the defect can be tiny |
| Free air (pneumoperitoneum) | Gas escaped the lumen | Can also come from other sources |
| Free fluid, no solid-organ injury | Leaked bowel contents or mesenteric blood | "Unexplained" fluid is the key phrase |
| Bowel wall thickening / abnormal enhancement | Bruised, ischemic, or devascularized wall | Underperfusion is easy to overcall or undercall |
| Mesenteric fat stranding / hematoma | The mesentery is bleeding or torn | Mild stranding is everywhere; degree matters |
| Active contrast extravasation | A vessel is actively bleeding right now | Needs contrast and a careful look |
Think of the bowel as a garden hose under pressure. A clean cut sprays everywhere — that's your free air and free fluid. But a crimp in the hose that pinches off the water supply is just as dangerous and far quieter; that's the devascularized segment with a dull, poorly enhancing wall. Both are emergencies. Only one of them is loud.
The single most useful phrase in this whole topic is "free fluid without a solid-organ injury." If there's a moderate amount of fluid in the belly and the liver, spleen, and kidneys all look fine, the bowel and mesentery just moved to the top of your suspect list. Don't shrug it off as "trace physiologic fluid" — especially in an adult male, who shouldn't have much to begin with.
Free air: trust it, but interrogate it
Gas outside the bowel lumen is a genuine red flag — but trauma muddies the water. A pneumothorax can track down, a chest tube or recent surgery can introduce air, and a tiny bubble might just be along for the ride. So free air earns your attention, but you confirm it's coming from a bowel injury and not a decoy. If the concept of gas where it doesn't belong is shaky, it's worth a detour through pneumoperitoneum, the dedicated page on free air.
The mesentery: where the bleeding hides
The mesentery is the fan-shaped sheet that suspends the bowel and carries its blood supply. Slam the abdomen hard enough and you can shear those vessels. The tells are a wedge of fluid or hematoma jammed between bowel loops (the "interloop" or triangular fluid sign), fat that looks dirty and streaky instead of clean and black, and — the one that gets the interventional team paged — a bright blob of contrast pooling outside a vessel.
That bright blob is active contrast extravasation — contrast leaving the vessel and puddling in real time. On the scan it looks like a fresh paint splatter that wasn't there a phase earlier. It means active bleeding, and it changes the plan from "watch and wait" to "do something now."
Beware the devascularized bowel segment that looks deceptively normal early. A loop whose mesenteric supply has been sheared may not show dramatic thickening for hours — and a poorly enhancing wall is easy to dismiss as a partial-volume artifact or a collapsed loop. If the mesenteric vessels in that region look disrupted, treat the quiet loop with suspicion, not relief.
Putting it together
No single sign is the answer here; the diagnosis is built from a pattern. Free air plus unexplained free fluid plus a thickened, oddly enhancing loop plus mesenteric stranding is a story, and the story is "this bowel is hurt." Ultrasound at the bedside — the FAST exam — can flag the free fluid that starts the whole conversation, but CT is what actually nails the injury.
When you see free fluid in the abdomen and every solid organ looks pristine, the bowel and mesentery are guilty until proven innocent. Stack the soft signs — they're far more convincing as a group than any one is alone.