The diagnosis is usually clinical and biochemical. The imaging questions are the CAUSE, the NECROSIS and the COMPLICATIONS — and timing decides what you can answer.
Orient first
- CT in the first 48–72 hours UNDERSTATES necrosis, because necrosis takes days to declare itself. An early scan that looks mild is not reassurance, and reporting it as such is a real harm.
- The two things that change management are the CAUSE (gallstones need intervention) and NECROSIS with its complications.
- Collections are named by age and content, and the names carry management: acute peripancreatic fluid collection and pseudocyst contain fluid; acute necrotic collection and walled-off necrosis contain solid debris. Calling walled-off necrosis a pseudocyst leads to a drain that fails.
Acquire the study
- Contrast-enhanced CT in the PORTAL VENOUS or pancreatic parenchymal phase — non-enhancing parenchyma is the definition of necrosis, so a non-contrast study cannot assess it. Say so explicitly if contrast was withheld for renal function.
- Time it: for severity assessment, ideally 72 hours or later after onset.
- Ultrasound is the study for the CAUSE — gallstones and duct calibre — not for severity.
- MRI/MRCP is better for duct integrity and for characterising solid debris within a collection.
The manoeuvre
- Assess the pancreatic parenchyma for enhancement, and estimate the PROPORTION that fails to enhance — that is the necrosis.
- Look at the peripancreatic fat and retroperitoneum for stranding and fluid.
- Characterise every collection: site, size, wall maturity, and crucially whether contents are pure fluid or contain SOLID debris.
- Look for the CAUSE: gallstones, a dilated CBD, a mass in the head, ductal disruption, features of chronic pancreatitis.
- Assess the vessels: splenic vein, portal vein and SMV thrombosis; pseudoaneurysm (especially splenic and gastroduodenal arteries) — this is the bleed that kills.
- Look for gas within the pancreas or a collection, which suggests infection.
- Assess the bowel: colonic cut-off, ileus, ischaemia of the transverse colon.
- Check the chest bases for effusions and consolidation.
What confirms it
- Non-enhancing pancreatic parenchyma on a properly contrast-enhanced study after 72 hours defines necrosis.
- Gas in a collection, or a new clinical deterioration with a collection, suggests infected necrosis.
What licenses you to exclude it
- ⚠️ A CT in the first 72 hours cannot exclude necrosis. Report the timing explicitly and say what the study can and cannot settle.
- A non-contrast CT cannot assess necrosis at all.
- Normal cross-sectional imaging does not exclude acute pancreatitis — the diagnosis is clinical and biochemical.
The classic misread
- Reporting "mild pancreatitis" on a day-1 scan.
- Calling walled-off necrosis a pseudocyst because the wall looks mature — look for solid debris inside.
- Missing a pseudoaneurysm because the arterial phase was never obtained in a patient who bled.
- Reporting severity from an ultrasound.