Cholangitis & PSC
- Ascending (acute bacterial) cholangitis is an infected, blocked bile duct — a plumbing emergency. The classic clue is fever + jaundice + right-upper-quadrant pain (Charcot's triad), and imaging hunts for the cause of the obstruction.
- Primary sclerosing cholangitis (PSC) is a chronic, slow-burn scarring of the bile ducts — not an infection, but the ducts narrow and scar over years.
- The PSC money shot on MRCP is a duct tree with alternating narrowings and dilations: a "beaded" or "string-of-beads" look, often described as pruned because the small branches drop out.
- PSC keeps two unpleasant companions: inflammatory bowel disease (especially ulcerative colitis) and a markedly raised lifetime risk of cholangiocarcinoma.
- MRCP is the workhorse for mapping the ducts without a needle; ERCP is reserved for when you also need to treat.
Two diseases share the word "cholangitis," and they could not be more different in tempo. One is a fire alarm going off tonight; the other is a house slowly settling on its foundations over a decade. Lumping them together is like filing "lightning strike" and "rust" under the same heading because both involve metal. Let's pull them apart.
Ascending cholangitis: the bile-duct emergency
Think of the bile duct as a drainpipe. Bile flows down it, into the gut, and as long as it keeps flowing, gut bacteria can't swim upstream. Block that pipe — usually with a stone slipped down from the gallbladder — and you've created a stagnant, warm, nutrient-rich pond. Bacteria throw a party. Pressure builds behind the blockage, and infected bile gets pushed back into the bloodstream. That's ascending cholangitis, and it can tip into sepsis fast.
Clinically, the giveaway is Charcot's triad: fever, jaundice, and right-upper-quadrant pain. Add confusion and low blood pressure and you've got Reynolds' pentad — which is the body's way of saying "this is now an emergency, please hurry."
Acute cholangitis is a clinical and lab diagnosis as much as an imaging one. Don't wait for a perfect picture to start treating — the job of imaging here is to find and relieve the obstruction, not to confirm the patient is sick.
Imaging's role is to answer one question: what's blocking the pipe, and where? Ultrasound is usually first — quick, no radiation, and good at spotting dilated ducts and gallstones. CT or MRCP follows to map the level of obstruction and look for the cause: a stone, a stricture, a tumor.
What you're actually looking for
The unifying imaging sign of obstruction is dilated bile ducts upstream of the blockage — the pipe backing up. On ultrasound or CT, dilated intrahepatic ducts run alongside portal vein branches and create the classic "too many tubes" or parallel-channel appearance. The wall of an infected duct may thicken and enhance.
Duct dilation tells you there's an obstruction, not what kind. A stone, a benign stricture, and a cholangiocarcinoma can all dam the same river. Always chase the cause at the point where the duct suddenly narrows — that transition point is where the answer hides.
Primary sclerosing cholangitis: the slow scarring
Now flip the tempo. PSC isn't an infection in a single blocked pipe — it's a chronic, immune-related inflammation that scars the bile ducts diffusely, throughout the tree, over years. Imagine a garden hose that's been kinked and crimped in a dozen random spots: some segments pinch down to nothing, the segments in between balloon out, and the whole thing looks lumpy and irregular.
That's the signature on MRCP (magnetic resonance cholangiopancreatography — an MRI tuned so that still bile-fluid lights up bright white, drawing the duct tree without contrast or a needle): multifocal strictures alternating with normal or dilated segments, giving a "beaded" or string-of-beads appearance. Because the small peripheral branches scar shut and disappear, the tree can look "pruned," like a shrub someone went after with hedge clippers.
PSC travels with company. It's strongly associated with inflammatory bowel disease, especially ulcerative colitis — so often that finding one should make you ask about the other. Over the long run, PSC also carries a substantially increased risk of cholangiocarcinoma, which is why these patients get watched closely.
A new dominant stricture in a known PSC patient — one focal area that's tighter and more mass-like than the rest — is a red flag for cholangiocarcinoma developing on top of the chronic disease. It earns a hard second look rather than a shrug.
Acute vs chronic, side by side
| Feature | Ascending cholangitis | PSC |
|---|---|---|
| Tempo | Acute, hours to days | Chronic, months to years |
| Cause | Infected, obstructed duct (often a stone) | Immune-mediated scarring of ducts |
| Classic sign | Charcot's triad (fever, jaundice, RUQ pain) | "Beaded," pruned ducts on MRCP |
| Best test | US first, then CT/MRCP to find the block | MRCP to map the duct tree |
| Big associations | Stones, acute cholecystitis | IBD; cholangiocarcinoma risk |
| Urgency | Emergency — relieve the obstruction | Surveillance and management |
MRCP vs ERCP: look versus do
One last point of confusion worth clearing. MRCP is purely diagnostic — a non-invasive MRI map of the ducts, no instruments inside the patient. ERCP (endoscopic retrograde cholangiopancreatography) threads a scope up to the duct opening and injects contrast — invasive, but it can actually fix things: pull out a stone, brush a stricture for cells, drop in a stent. The modern rhythm is to look first with MRCP, and reach for ERCP when you also need to intervene.
If you remember nothing else: same root word, opposite stories. Ascending cholangitis is a blocked pipe on fire tonight. PSC is the slow, beaded scarring of the whole plumbing system — patient, chronic, and worth watching for the day it turns into something worse.