Cardiac Masses & Thrombus
- Most "masses" in the heart are not tumors at all. The big three to think of first are thrombus, normal anatomy faking you out, and benign tumors — true cancer of the heart is rare.
- Of the actual tumors, metastasis is far more common than a primary cardiac tumor. The heart is much more often a guest house than a place where cancer is born.
- Thrombus loves stagnant blood: a poorly contracting left ventricle after an infarct, or a fibrillating left atrial appendage. Look where the blood is sitting still.
- The single most useful trick is does it light up with contrast? Tumors have a blood supply and enhance; bland thrombus has none and stays dark.
- Cardiac MRI is the problem-solver — it tells you what the mass is made of (fat, fluid, blood, vascular tissue) when CT and echo just shrug.
You find a blob in the heart. Your pulse quickens, you whisper "cancer," and you start drafting the bad-news report. Stop. Take a breath. Statistically, you are almost certainly wrong, and the heart is one of the few places in the body where "I see a mass" usually has a happy ending. Let me walk you through how to keep your cool.
First, rule out the impostors
Before you diagnose anything, remember that the heart is full of normal lumps and bumps that look alarming if you forget they exist. The crista terminalis, the pectinate muscles, a chunky moderator band, a prominent Eustachian valve, or a wad of fat in the interatrial septum (lipomatous hypertrophy) all routinely get mistaken for tumors by people who are having a long day.
Lipomatous hypertrophy of the interatrial septum classically spares the fossa ovalis, giving a "dumbbell" shape. It is just fat — bright on T1, drops out on fat-saturated sequences — and it is benign. Do not biopsy a normal fat pad.
So the real list of things that make a mass is short: a clot, a tumor, or a vegetation/abscess from infection. That is genuinely most of it.
Thrombus: the most common "mass" by a mile
If blood stops moving, it clots. That is true in a varicose vein and it is true in your heart. So the question with any cardiac mass is: where is the blood sitting still?
Two classic stagnation zones:
- The left ventricular apex after a big anterior heart attack — the muscle there is dead, akinetic, and the blood just pools like water in a dented bucket.
- The left atrial appendage in atrial fibrillation — a little blind pouch where, when the atrium quivers instead of squeezing, blood eddies and curdles.
The reason we care so much is that left-sided clot can break off and fire an embolus straight to the brain. That is a stroke waiting to happen, so calling thrombus correctly genuinely changes the patient's day.
The enhancement trick: the whole game in one question
Here is the lever that does most of the work: does the thing have a blood supply?
A tumor grew its own vessels, so when you give iodinated contrast (CT) or gadolinium (MRI), it lights up. Bland thrombus is just packed-up dead blood with no plumbing, so it stays stubbornly dark. On cardiac MRI, an early-gadolinium or long-inversion-time late-enhancement sequence makes thrombus pop out as an inky black void while everything around it brightens.
This is exactly why cardiac MRI is the referee. The way different tissues behave across sequences — fat, fluid, vascular tumor, bland clot — is the heart of the cardiac MRI toolkit. If you only remember one application, it is "tumor enhances, thrombus doesn't."
The benign tumors you should know
Among actual primary tumors — which are rare to begin with — most are benign. A few worth recognizing:
| Tumor | Where it lives | The tell |
|---|---|---|
| Myxoma | Usually left atrium, often hanging off the interatrial septum near the fossa ovalis | Mobile, on a stalk, can flop toward the mitral valve and cause symptoms when the patient changes position. The most common primary cardiac tumor in adults. |
| Papillary fibroelastoma | Heart valves | Tiny, frond-like, mobile; small but can throw emboli. |
| Lipoma | Anywhere | Pure fat — bright on T1, suppresses with fat-sat. Boring, and that is good. |
| Rhabdomyoma | Ventricular muscle | The classic tumor of infants; strongly associated with tuberous sclerosis. |
| Fibroma | Ventricular wall, often in kids | Solid, can calcify. |
A mobile mass on a stalk in the left atrium pointing at the mitral valve is a myxoma until proven otherwise. A tiny mobile frond on a valve leaflet is a papillary fibroelastoma until proven otherwise. Location and motion do a lot of the diagnostic lifting here.
When it really is cancer
Two flavors of bad news. First, metastasis — and this is the one to keep front of mind, because secondary tumors reach the heart far more often than the heart grows its own. Melanoma is notorious for it; lung and breast cancer and lymphoma get there too, often by direct invasion or via the great veins.
Second, primary malignancy, almost always a sarcoma (angiosarcoma being the classic, with a fondness for the right atrium). The features that should worry you are the usual aggressive-mass story: broad-based attachment rather than a tidy stalk, invasion across tissue planes, a bloody pericardial effusion, and avid, messy enhancement.
A new mass plus a hemorrhagic pericardial effusion is a red flag for malignancy, especially angiosarcoma. A bloody effusion can also tip into tamponade — see pericarditis and constriction for why the pericardium punches above its weight.
Putting it together
When you spot a cardiac mass, run the same little checklist every time: Is it normal anatomy? Is the blood stagnant nearby (think thrombus)? Does it enhance (think tumor)? If it's a tumor, benign features or aggressive ones? CT and echo find the thing; cardiac MRI tells you what it's made of and whether it has a blood supply. Tissue characterization on MRI overlaps heavily with how we read scar and viability — the same late-gadolinium logic from myocardial infarction and viability is doing double duty here.
The one sentence to carry out the door: most cardiac masses are thrombus or benign, true primary cancer is rare, and the enhancement question sorts out almost everything.