Ruptured Abdominal Aortic Aneurysm
- A ruptured abdominal aortic aneurysm (AAA) is a balloon in the main pipe of the belly that has finally split — blood is escaping into the body, and the clock is now measured in minutes.
- The classic trio is sudden abdominal or back pain, low blood pressure, and a pulsatile mass — but plenty of patients show up looking deceptively unimpressive.
- On CT you are hunting for two things: a dilated aorta (the aneurysm) and blood where it shouldn't be (the rupture). The second one is the emergency.
- If the patient is crashing, this is a clinical diagnosis. You don't wait for a perfect scan; you tell the surgeon and you tell them now.
Imagine an old garden hose that's been bulging at one spot for years — a thin, stretched, weakening dome. It might hold for a long time. But the day it finally bursts, water doesn't politely trickle out; it sprays everywhere at once. Now swap the garden hose for the abdominal aorta — the largest artery in the body, the high-pressure trunk line that channels the heart's output down toward the legs — and you have a sense of the urgency. A ruptured AAA is one of the few things in radiology where being five minutes slow genuinely changes who lives.
What an aneurysm is (and when it gets scary)
An abdominal aortic aneurysm is a permanent, focal widening of the aorta — the wall has grown weak and ballooned outward. Most of the time these are found incidentally, sitting there quietly, and they get watched over years.
The danger isn't the aneurysm existing; it's the aneurysm failing. As the wall stretches, it thins, and a thin wall under arterial pressure is a wall living on borrowed time. When it gives way, you go from "interesting finding on an outpatient scan" to "the surgical team is sprinting" in a single heartbeat.
A ruptured AAA is a true surgical emergency. A meaningful fraction of patients never reach the hospital, and even those who do face a serious risk of dying. Speed of recognition and communication is part of the treatment.
The two things CT has to answer
When a contrast-enhanced CT of the abdomen and pelvis comes up with this question, your brain should split the problem cleanly in two.
Question one: is there an aneurysm? Look at the aorta in cross-section. A normal abdominal aorta is a tidy circle; an aneurysm is a fat, dilated one, often stuffed with a rind of clot (mural thrombus) lining the inside.
Question two: has it ruptured? This is the one that matters tonight. You are searching for blood outside the aortic wall — most often in the retroperitoneum, the space behind the abdominal cavity where the aorta lives. Fresh blood on CT looks denser and more "stuffed in" than the normal fat back there. The neat fat planes get replaced by a smudgy, crowding density that shouldn't be there.
Reading the wall itself
Sometimes you catch the aorta in the act of failing. A couple of signs on a non-contrast or contrast scan point to a wall that is unstable or actively bleeding.
| Sign | What you're seeing | Why it matters |
|---|---|---|
| Retroperitoneal hematoma | Blood pooling behind the abdominal cavity, around the aorta | The direct evidence of rupture |
| Active contrast extravasation | Contrast leaking out beyond the wall on a contrast scan | Bleeding right now — extremely urgent |
| "Crescent sign" | A crescent of higher density within the aneurysm's mural thrombus | A clue the wall is acutely unstable |
If you want a refresher on how contrast lights up flowing blood (and therefore makes a leak visible), the page on iodinated contrast is worth a detour.
Don't anchor on "the patient looks fine, so the aorta is fine." A contained rupture — where surrounding tissue temporarily tamponades the bleed — can look surprisingly stable for a short while before it lets go catastrophically. The CT findings of retroperitoneal blood outrank the patient's comfortable appearance every time.
The mimics that will fool you
The symptoms of a ruptured AAA are great impostors. Sudden back pain plus a wobble in blood pressure gets blamed on a kidney stone, a pulled muscle, or "probably just gastro." Older patients with belly and flank pain deserve a hard look at their aorta before anyone settles on a cozier diagnosis.
It's also a cousin of aortic dissection, where the aortic wall splits into layers rather than blowing outward. Different problem, overlapping panic, and the CT distinguishes them — so the trick is simply to think of the aorta in the first place.
How not to miss it
When you sit down to a belly CT in an older patient with pain — especially the approach you'd take for any abdominal CT — make the aorta a deliberate stop on your checklist, not an afterthought you glance at on the way out.
Two findings, in order: a dilated aorta tells you the aneurysm exists; blood outside the wall tells you it has ruptured. The second finding is a phone call to the surgeon, made before you've finished dictating.
If there's blood around an aneurysmal aorta, you don't sit on it, you don't wait for the next radiologist, and you don't bury it in the middle of a long report. You pick up the phone. That single habit is the whole point of a don't-miss diagnosis: the imaging is only as good as how fast the right person hears about it.