First and second year — the floor first, then every step
Is it communicating with the duct (branch-duct IPMN), and does it have worrisome features or high-risk stigmata? Those, not the cyst's name, drive surveillance, EUS or surgery.
Orient first
Most incidental small pancreatic cysts are side-branch IPMNs; the others to know are serous cystadenoma (microcystic, central scar), mucinous cystic neoplasm (women, body/tail, no communication) and pseudocyst (after pancreatitis).
High-risk stigmata (enhancing mural nodule ≥ 5 mm, main duct ≥ 10 mm, obstructive jaundice from a head lesion) and worrisome features (cyst ≥ 3 cm, enhancing thick wall, main duct 5–9 mm, nodule < 5 mm, abrupt duct calibre change with atrophy, rapid growth) come from the Fukuoka/international consensus — verify the revision used.
MRCP shows duct communication best.
Acquire the study
Heavily T2-weighted 3D MRCP, T2, DWI, dynamic post-contrast T1.
The manoeuvre
MRCP: communication of the cyst with the main duct (branch-duct IPMN) on the source images.
Main duct diameter in mm; abrupt calibre change and upstream atrophy.
Cyst size (maximum diameter) and internal septa; microcystic "honeycomb" with a central scar (serous).
Post-contrast: enhancing mural nodule (measure) or thick enhancing wall.
Compare with priors for growth rate.
What confirms it
A classification (likely BD-IPMN, serous, mucinous, pseudocyst) with the list of worrisome features and high-risk stigmata present or absent.
What licenses you to exclude it
A cyst without worrisome features or stigmata is managed by surveillance intervals, not excluded as neoplasm.
The classic misread
Calling an enhancing nodule a debris ball — non-enhancing mucin plug moves and does not enhance on subtraction.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Main pancreatic duct · diameter in the head/bodyup to 3 mm
Tapers toward the tail; mild age-related dilatation is recognised.
USG · CT · MRI
Diagnostic criteria
Pancreatic cyst · Worrisome features (IPMN surveillance)
cyst 3 cm or more, main pancreatic duct 5–9 mm, or an enhancing mural nodule are "worrisome features"; main duct 10 mm or more is a high-risk stigma
These are DISEASE-MANAGEMENT thresholds, not normal limits — the normal main pancreatic duct is up to 3 mm (see the separate reference value). The consensus has been revised more than once; verify the current edition and note that the ACR incidental-cyst white paper uses different follow-up tables. Versioned criterion — verify against the current edition before clinical use.
CT · MRI
Pancreatic cyst (high-risk stigmata) · High-risk stigmata (IPMN) — how to report them
a named criteria set: obstructive jaundice with a cyst in the pancreatic head, an enhancing mural nodule, or a main-duct calibre of 10 mm or more are high-risk stigmata in the Fukuoka consensus
High-risk and worrisome are DIFFERENT rows of the same table — do not collapse them. The consensus has been revised; verify the current edition, and remember the ACR incidental-cyst white paper uses a different follow-up architecture. Versioned criterion — verify against the current edition before clinical use.
CT · MRI
Pancreatic duct (IPMN type) · Main-duct versus branch-duct versus mixed
branch-duct = a cyst that communicates with the MPD and the MPD is not dilated. Main-duct = a dilated MPD (already-registered Fukuoka: 5–9 mm worrisome, ≥10 mm high-risk stigma). Mixed = both. Type is not a single cyst millimetre
Main-duct and mixed-type are a different risk conversation from a tiny branch-duct cyst. Do not invent an edition year. Versioned criterion — verify against the current edition before clinical use.
MRI · CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.