A weak spot in the body main pipe quietly stretches for years, then can tear without warning. Learn who to screen, the size and growth numbers that send it to surgery, and the rupture triad that means the operating room, not the scanner.
The Setup
A Weak Spot in the Pipe
An aneurysm is not a clot or a blockage. It is a wall that has lost its strength and ballooned outward. Walk the chain once and why it grows, and who grows it, falls into place.
A 69-year-old man with a 40-year smoking history comes in for a routine visit feeling fine. On exam the physician feels a pulsing, expansile fullness in the middle of his upper abdomen. He has no pain. An ultrasound measures the aorta at 4.1 cm.
What single process best explains this finding?
Start with the wall. An aneurysmA permanent focal dilation of an artery to at least 1.5 times its normal diameter. For the abdominal aorta, normal is about 2 cm, so 3 cm or more counts as an aneurysm. is a permanent ballooning of the aorta to 3 cm or more (the normal abdominal aorta is about 2 cm). The supporting proteins in the wall, elastin and collagen, get chewed up by enzymes called matrix metalloproteinases → the wall thins and weakens → the pressure of every heartbeat pushes the weak spot outward. Most sit below the kidney arteries (infrarenal).
Why it only gets worse. Once it starts bulging, physics takes over. Wall tension rises as the radius grows (the law of Laplace), so a bigger aneurysm has more tension pulling its already-weak wall apart, which makes it grow faster, which raises the tension again. That runaway loop is why rupture risk climbs steeply once the diameter passes about 5.5 cm.
Who grows one? Flip each card.
The biggest riskTap to flip
SmokingThe strongest modifiable risk factor for forming, growing, and rupturing an AAA. It is also why screening targets people who have ever smoked, and why quitting is the single best medical intervention.
The profileTap to flip
Older man, vascular historyMale sex, age over 65, high blood pressure, atherosclerosis, and a family history all raise the risk. The typical AAA patient is an older man with a long smoking and cardiovascular history.
The exceptionTap to flip
Connective tissue means thoracicMarfan and similar connective tissue disorders weaken the wall too, but they classically produce thoracic aortic aneurysms in younger patients, not the infrarenal abdominal kind driven by smoking and atherosclerosis.
At the Bedside
Silent, Then Catastrophic
Most aneurysms whisper nothing until the day they tear. Learn the quiet sign and the loud one, and the disguise rupture wears in the emergency department. Tap each card.
Usually silent
Tap to reveal
The large majority are asymptomatic and found by chance on imaging or as an incidental pulsatile mass on exam. That silence is exactly why screening exists, you catch it before it speaks.
Pulsatile mass
Tap to reveal
A pulsing, expansile fullness in the mid-upper abdomen. It is the classic physical finding, though exam alone is insensitive, especially in larger patients.
The rupture triad
Tap to reveal
Sudden severe abdominal, flank, or back pain plus hypotension plus a pulsatile mass. This trio in an older smoker is a ruptured AAA until proven otherwise, and it is a surgical emergency.
The great mimic
Tap to reveal
A rupturing AAA can look just like a kidney stone, sudden flank or back pain in an older patient. Anchoring on renal colic and missing the aorta is a classic, fatal trap.
From the Attending
An older smoker with new flank or back pain is not allowed to be a simple kidney stone until you have looked at the aorta. First stones are uncommon after 60, and a ruptured aneurysm wears the exact same costume. Put the ultrasound probe on the belly before you write renal colic.
Catching It
Who Gets Scanned, and How
The right test depends entirely on the question: screen the well, plan in the stable, and do not move the crashing patient an inch toward the scanner. Try each step before you reveal it.
A well 68-year-old man with a 30-pack-year smoking history and no symptoms. What screening test do you offer?
A one-time abdominal ultrasound is recommended for men aged 65 to 75 who have ever smoked. It is sensitive, quick, cheap, and radiation-free, perfect for screening a silent disease. Ever-smoked man 65 to 75 gets a one-time screening ultrasound.
A stable patient has a known AAA and now reports dull back pain. Blood pressure is normal. Best imaging to plan the next move?
When the patient is stable, CT angiography gives the precise anatomy (size, shape, relationship to the kidney arteries) needed to plan an operation and to look for a contained leak. Stable and symptomatic means CT angiography for the surgical roadmap.
An older smoker arrives with sudden back pain, a pulsatile mass, and a blood pressure of 78/44. What now?
An unstable patient with a suspected rupture does not get sent to the scanner, they can die inside it. Confirm with a bedside ultrasound and go straight to the operating room. Resuscitate gently (permissive hypotension), because driving the pressure up can pop the clot holding the leak. Unstable rupture means the operating room, not the CT.
The Plan
Watch It, or Fix It
You do not operate on every aneurysm, surgery carries real risk. You wait until the danger of rupture outweighs the danger of the operation. The numbers are the whole game.
The thresholds for repair. Offer elective repair when the diameter reaches 5.5 cm in men (about 5.0 cm in women), when it grows rapidly (more than 0.5 cm in 6 months, or more than 1 cm in a year), or when it becomes symptomatic at any size. Below those numbers, the rupture risk is low and you watch instead of cut.
Aortic diameter
What to do
Under 3.0 cm
Not an aneurysm. No surveillance needed.
3.0 to 3.9 cm
Surveillance ultrasound every 2 to 3 years.
4.0 to 4.9 cm
Surveillance ultrasound every 6 to 12 months.
5.5 cm or more (men)
Elective repair. (Women often repaired near 5.0 cm.)
Rapid growth
Repair if it grows more than 0.5 cm in 6 months or more than 1 cm in a year.
Symptomatic
Repair regardless of size. Pain or tenderness can herald rupture.
Open versus endovascular. Elective repair is either open surgery (replace the segment with a graft) or EVAR, an endovascular repair that threads a stent-graft up through the groin arteries. EVAR has lower up-front operative mortality and a faster recovery, but it demands lifelong surveillance for an endoleak (blood leaking around the graft back into the sac). Open repair is more durable and needs less follow-up. Alongside either, the medical plan is the same backbone of vascular care: stop smoking, control blood pressure, and treat with a statin.
Board Trap
The most tempting wrong answer in a ruptured AAA is order a CT scan. A patient with a blood pressure of 70/40 and a pulsatile mass will die in the scanner. Unstable plus pulsatile mass equals bedside ultrasound and the operating room. Save the CT for the stable patient who has time for a surgical roadmap.
From the Attending
A 4.5 cm aneurysm does not get an operation, it gets an ultrasound every 6 to 12 months and a hard conversation about cigarettes. Quitting smoking slows growth more than any pill. Do not let a patient talk you into fixing a small, quiet aneurysm, and do not let one talk you out of repairing a 5.7 cm one. Respect the numbers in both directions.
Prove It
Board Walkthrough
Six original clinical vignettes, 5 dealt per round, answer choices shuffled, never repeating within a round. Tap a wrong answer first to see why it almost works, then read the glowing clues.
Medically reviewed by Kaitlyn Cocuzzo, MD and Fatima Ali, DO · Last reviewed June 2026
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