Pulmonary Infarct
- A pulmonary infarct is lung tissue that actually dies downstream of a blocked artery — most often a clot, so it's usually the angry sequel to a pulmonary embolism.
- It's surprisingly uncommon, because the lung has a backup blood supply. When it does happen, it's typically peripheral and wedge-shaped, pointing at the lung edge.
- The classic CT clues are a pleura-based wedge of consolidation, sometimes with a "reverse halo" (lucent center, denser rim) and little internal bubbles of preserved air.
- It often coexists with a small pleural effusion, and on follow-up it shrinks toward the pleura ("melting ice cube") instead of clearing like pneumonia.
Here's a fact that trips people up: the lung is one of the few organs that can have its main artery to a region completely plugged and mostly just... shrug it off. So when a piece of lung genuinely dies, it's a bit of an event. That dead, hemorrhagic wedge is the pulmonary infarct, and it has a look all its own.
Why the lung usually gets away with it
Most organs run on a single plumbing line. Block it and everything downstream starves. The lung cheated: it has a dual blood supply. The pulmonary arteries carry the big flow, but the bronchial arteries (off the aorta) run a quiet little parallel circuit, and the alveoli can even grab oxygen straight from the airways. So a clot in a pulmonary artery is like one of two garden hoses to your lawn getting kinked — the grass is unhappy, but the second hose often keeps it alive.
That redundancy is exactly why true infarction is the exception after a PE, not the rule. The patients who do infarct tend to be the ones whose backup circuit is already compromised — think poor cardiac output or underlying lung disease — so the spare hose was barely dribbling to begin with.
Don't conflate "PE" with "infarct." A pulmonary embolism is the clot in the pipe; an infarct is dead lung tissue that sometimes results. Most PEs never infarct. The infarct is the downstream casualty, not the embolus itself.
What it looks like
Because the culprit is a clot lodged in a smaller, more peripheral artery, the dead tissue sits out at the lung's edge against the pleura. Picture a slice of pie: the wide crust is the pleural surface, and the tip points inward toward the hilum where the blocked vessel was. That pleura-based wedge is the signature.
On a chest radiograph this can show up as a rounded or wedge-shaped opacity hugging the lung periphery, sometimes called a Hampton hump — a dome-shaped density sitting on the pleura with its convex bump facing inward. It's a lovely sign and also a slightly unreliable one; plenty of infarcts are subtle or invisible on plain film.
CT is where it earns its keep. On CT you're hunting for that same wedge of consolidation jammed against the pleura, and a few extra tells often come along:
| Feature | What you see | Why it happens |
|---|---|---|
| Pleura-based wedge | Triangular consolidation, broad base on pleura, apex toward hilum | Dead tissue maps to the territory of the occluded peripheral artery. |
| Reverse halo / "atoll" sign | Lucent or ground-glass center with a denser ring around it | Central tissue resolves or is less hemorrhagic than the rim. |
| Internal lucencies | Little bubbles of preserved air inside the wedge | Air-containing structures survive even as tissue dies. |
| Vessel sign | A vessel seen leading right into the apex of the wedge | That's the occluded artery feeding the dead territory. |
| Small effusion | A sliver of fluid on the same side | Irritated pleura weeps a reactive effusion. |
Don't mistake it for pneumonia
This is the trap, and it's a good one. A peripheral consolidation with a small effusion also describes a basic pneumonia, and the two get confused constantly.
A pulmonary infarct and a peripheral pneumonia can look near-identical on a single scan. The tiebreakers: an infarct is wedge-shaped with a pleural base, often shows the reverse-halo sign and internal air bubbles, frequently has a feeding vessel at its apex, and — critically — sits downstream of a clot you can often find on a CT pulmonary angiogram. Pneumonia loves an air bronchogram; infarcts usually don't.
The other big tiebreaker is time. Pneumonia clears like fog lifting — patchy, all over, often resolving from the outside in or just fading. An infarct does its own thing on follow-up: it shrinks toward the pleura, keeping its shape but getting smaller, the way an ice cube melts down without changing into a puddle of a different shape. Radiologists actually call this the "melting ice cube" sign, and it's one of the more honest pieces of jargon we have.
If a peripheral consolidation is melting toward the pleura on serial scans rather than clearing diffusely, think infarct and go back and scrutinize the pulmonary arteries — the clot that caused it may still be sitting there.
Why we care
A pulmonary infarct is a flag that says there is, or was, a meaningful clot here — which means the workup and management orbit around the embolism, not the dead wedge itself. The infarcted tissue typically heals into a small scar or a thin pleural-based line and doesn't need treating on its own. It can also coexist with the broader picture of chronic clot burden and pulmonary hypertension when emboli pile up over time.
So the one thing to carry out of here: when you see a wedge of consolidation parked against the pleura with a reverse halo and a vessel pointing at its tip, don't just call it consolidation and move on. Ask what plugged the artery that fed it — because the infarct is the smoke, and the clot is the fire.