Pericarditis & Constriction
- The pericardium is a two-layer sac around the heart. Pericarditis is when that sac gets inflamed; constriction is when it later stiffens into a rigid shell that squeezes the heart.
- The number you hunt for is thickness: a normal pericardium is a hair-thin line, and a thick one (think a few millimeters or more) is the red flag for constriction.
- Constriction's signature is a stiff sac throttling how the heart fills — so the imaging story is all about filling, not pumping.
- The classic mimic is restrictive cardiomyopathy: same "can't fill" physiology, totally different fix. Pericardium thick = surgery can help; muscle stiff = it can't.
- Late-gadolinium enhancement on cardiac MRI lights up an inflamed, angry pericardium — handy for spotting the active, potentially reversible kind.
Your heart lives inside a fitted bag. Most of the time you never think about it, the same way you never think about the case your phone lives in — until the case shrinks two sizes and starts crushing the phone. That, in one sentence, is the journey from pericarditis to constriction.
What the pericardium actually is
The pericardium is a double-layered sac. Picture a water balloon with your fist pushed into it: your fist is the heart, the layer hugging your knuckles is the visceral layer, and the outer wall of the balloon is the parietal layer (backed by a tough outer coat of fibrous tissue — the part that scars and stiffens). Between them sits a teaspoon-ish film of lubricating fluid so the heart can wiggle without chafing.
On a normal CT or MRI, that whole sac shows up as a pencil-thin dark line, usually best seen in front of the right heart where a little fat outlines it. If you can barely find it, that's the healthy look.
Pericarditis: the sac gets angry
Pericarditis is inflammation of that sac. Clinically it's sharp chest pain that famously gets better when the patient leans forward — the one exam-room detail that sticks. On imaging, the inflamed pericardium thickens, may grab contrast, and often comes with a little extra fluid (a small pericardial effusion).
The star tool here is cardiac MRI. On late-gadolinium-enhancement (LGE) imaging, an actively inflamed pericardium lights up bright — the gadolinium seeps into the inflamed tissue and lingers. Think of it like a bruise glowing under a blacklight.
That bright, enhancing pericardium isn't just pretty — it usually means active, ongoing inflammation, which is the kind that may calm down with medical treatment. A pale, non-enhancing, just-thick sac is more likely old, burnt-out scar.
Constriction: when the bag turns to leather
Sometimes that inflamed sac heals badly. Instead of going back to thin and floppy, it scars, thickens, and sometimes calcifies into a stiff, unyielding shell. Now the problem flips: the heart muscle pumps fine, but the rigid box won't let it fill. Every heartbeat, the ventricles try to expand to take in blood and slam into a wall.
The tells:
- A thick pericardium — the single best CT/MRI clue. The thicker it is, the more it argues for constriction.
- Pericardial calcification — CT is the champion for this. A curving rind of calcium around the heart is about as specific a sign as cardiac imaging gives you.
- Squeezed, tube-like ventricles and big, backed-up systemic veins (a fat inferior vena cava, congested liver) because blood can't get in, so it dams up behind the heart.
On real-time cine MRI you can even watch the physiology: with each breath, the stiff sac forces the two ventricles to compete for a fixed space, so the wall between them (the septum) bounces and shudders. Radiologists call it septal bounce. It's the heart's two roommates fighting over a bed that's too small.
The mimic you must not miss
Here's the trap. Restrictive cardiomyopathy produces nearly identical "the heart can't fill" symptoms — but there the muscle itself is stiff and the pericardium is innocent. The distinction is enormous, because constriction can often be cured by surgically stripping off the bad pericardium, while a stiff muscle gets no benefit from that operation at all.
| Feature | Constrictive pericarditis | Restrictive cardiomyopathy |
|---|---|---|
| The stiff part | The pericardium (the sac) | The myocardium (the muscle) |
| Pericardial thickness | Often thickened | Usually normal |
| Calcification | Can be present, very suggestive | Absent |
| Septal bounce on cine | Classically present | Usually absent |
| Fix | Pericardiectomy can help | Pericardium surgery won't help |
Don't treat a normal-thickness pericardium as a free pass. A meaningful minority of surgically proven constriction has a pericardium that measures normal — so if the filling physiology screams constriction, trust the physiology (septal bounce, respiratory variation) over the ruler.
This overlap is exactly why constriction and restrictive cardiomyopathy are taught as a matched pair — same symptoms, opposite culprits.
The one thing to carry out
When the heart can't fill, ask whose fault is it — the bag or the muscle? CT finds the calcified, leathery sac; MRI shows you whether it's actively inflamed (bright on LGE, possibly treatable) or burnt-out scar, and catches the tattletale septal bounce. Get the bag-versus-muscle answer right and you've pointed the patient toward the operation that helps — or saved them from one that wouldn't.