Pulmonary Hypertension
- Pulmonary hypertension (PH) is chronically high pressure in the lung's arteries — the right heart's pipes are clogged or stiff, and it has to shove blood through anyway.
- The diagnosis is made by measuring pressure (right heart catheterization), not by imaging — but imaging is how you suspect it and hunt for a cause.
- The classic CT clue: a fat main pulmonary artery, especially when it's wider than the aorta sitting next to it.
- The downstream story is a strained right ventricle — dilated, thick-walled, and eventually shoving the septum the wrong way.
- It's a syndrome with many parents (lung disease, clots, left heart failure, primary vessel disease), and the imaging often points you at which parent.
Imagine the right side of your heart as a polite, low-pressure pump. It was built to push blood into the lungs across a soft, sprawling, low-resistance network — like watering a garden through a hundred wide, floppy hoses. It barely has to try. Pulmonary hypertension is what happens when those hoses get narrowed, stiff, plugged, or backed up, and that gentle pump suddenly has to push against a brick wall. The pressure climbs, and the right heart — which never signed up for heavy lifting — slowly buckles.
That's the whole drama. Everything below is just where the brick wall came from and how you spot the strain.
What "high pressure" actually means
Radiologists love to act like they diagnose this on a scan. We don't, really. PH is officially defined by an elevated mean pulmonary arterial pressure measured with a catheter threaded into the right heart — the gold standard, full stop. Imaging is the detective work around that number: who's at risk, what's causing it, and how badly the right ventricle is paying for it.
So when I say "PH on CT," I mean findings that should make you say the words out loud and recommend the catheter, not a final verdict.
The big fat pulmonary artery
The signature imaging finding is enlargement of the main pulmonary artery (the trunk that leaves the right ventricle). The handy trick: compare it to the ascending aorta lying right beside it on the same axial CT slice. When the pulmonary artery is wider than the aorta, that's suspicious for elevated pressure.
The analogy I can't shake: it's like a hose that's been left under pressure so long it's permanently ballooned out near the spigot. The lung arteries do the same — big and proud at the center, then tapering away sharply toward the edges (sometimes called pruning, like a tree trimmed back at the branches).
The "pulmonary artery wider than aorta" sign is a useful flag, but it's not a pressure gauge. Plenty of caveats apply, and a normal-sized artery doesn't rule PH out. Treat it as "go ask the cardiologist," not "case closed."
Following the strain downstream
Pressure that high doesn't just sit in the artery — it punishes the pump behind it. So the second half of the imaging story is the right ventricle (RV).
A chronically overworked RV does what any overworked muscle does: it bulks up (the wall thickens) and then, when it can't keep up, it stretches and dilates. On a CT or cardiac MRI you may see the RV looking as big as — or bigger than — the left ventricle, which is backwards from normal.
The dramatic one is septal flattening or bowing: the wall between the ventricles, normally curving nicely toward the right, gets shoved toward the left by the high right-sided pressure. On a short-axis image the left ventricle stops looking like a plump circle and starts looking like a D. That D-shape is the heart practically narrating its own pressure problem.
A dilated right ventricle plus a septum bowing toward the left ("D-shaped LV") tells you the high pressure is real enough to be reshaping the heart — and that the RV is in trouble.
Many doors into the same room
PH isn't one disease; it's a destination several roads lead to. Clinically it's sorted into groups, and the imaging often hints at which road the patient took:
| Cause | What you may see on imaging |
|---|---|
| Left heart failure (the most common overall) | Enlarged left atrium/ventricle, pulmonary edema — pressure backed up from downstream. |
| Chronic lung disease | Emphysema or fibrosis chewing up the lung vessels — the bed itself is destroyed. |
| Chronic clots (chronic thromboembolic PH, CTEPH) | Old, organized pulmonary embolism — webs, bands, and abruptly cut-off or narrowed arteries. |
| Primary arterial disease | Big central arteries with pruned peripheral branches and no obvious culprit elsewhere. |
This matters enormously, because the treatment splits hard by cause. The most important fork: chronic-clot disease (CTEPH, chronic thromboembolic PH) can sometimes be cured surgically, so spotting old, organized clot — distinct from a fresh pulmonary infarct — is one of the genuinely high-stakes calls.
Don't confuse old, organized thromboembolic disease with an acute clot. Acute PE is a fresh filling defect in a normal-caliber vessel; chronic disease shows webs, bands, wall-hugging crescents, and vessels that are narrowed or weirdly tapered. Calling chronic clot "acute PE" sends the patient down the wrong treatment road.
The one thing to carry out
Pulmonary hypertension is a plumbing-and-pump story: the lung arteries get hard to push through, and the right heart pays for it. On imaging you suspect it from a fat central pulmonary artery and a strained, dilated right ventricle — then your real job is chasing down why, because the cause decides everything that happens next.