Emerging Issue - Fatty Pancreas in Pancreatic Cystic Neoplasms: Results of a Matched Case-Control Study.

Kyoto 2024 (IAP) applies a single HRS/WF risk-stratification algorithm to all IPMN, including main-duct and mixed types. Workup uses a combination of MDCT, MRI/MRCP, and EUS plus blood tests (tumor markers, HbA1c) per institutional policy, the guideline considers MDCT, MRI, and EUS equivalent for diagnosis rather than designating MRI/MRCP as the single preferred initial modality; new in 2024, EUS imaging and EUS-FNA cytology are folded into the HRS/WF assessment when EUS is performed. High-risk stigmata (HRS): (1) obstructive jaundice in a patient with a cystic lesion of the pancreatic head, (2) enhancing mural nodule >=5 mm or a solid component, (3) main pancreatic duct >=10 mm, and (4) suspicious or positive cytology if EUS-FNA was done. Worrisome features (WF): (1) acute pancreatitis, (2) elevated CA19-9 (>37 U/mL), (3) new-onset or acute exacerbation of diabetes within the past year, (4) cyst >=30 mm, (5) enhancing mural nodule <5 mm, (6) thickened/enhancing cyst walls, (7) MPD >=5 and <10 mm, (8) abrupt change in duct caliber with distal parenchymal atrophy, (9) lymphadenopathy, and (10) cyst growth rate >=2.5 mm/year. Importantly, Kyoto deliberately keeps the 'HRS/WF' framing rather than 'absolute/relative indication': the operative decision is a careful multidisciplinary judgment weighing the degree of suspicion for high-grade dysplasia/invasive carcinoma AGAINST the patient's general condition, comorbidity, life expectancy, and preference, HRS should trigger consideration of resection, not automatic resection, and WF should prompt EUS and multidisciplinary evaluation, with EUS-FNA cytology/molecular sampling reserved for cases in which its results would actually alter management (per Kyoto, the indication for cyst-fluid sampling by EUS-FNA is limited to when further management will be altered according to the results, and FNA should not be performed when HRS is already obvious on MDCT/MRI and surgery is otherwise indicated). MD-IPMN and mixed IPMN are managed by the SAME algorithm, with the surgical decision driven by suspicion for invasive carcinoma and the goal of a negative margin, not by main-duct involvement alone. Non-resected BD-IPMN enters size-stratified surveillance: <20 mm, at 6 months once, then every 18 months if stable; 20 to <30 mm, every 6 months x2, then every 12 months if stable; >=30 mm, every 6 months. On discontinuing surveillance, Kyoto offers TWO options for small unchanged BD-IPMN ('stop surveillance' vs 'continue surveillance' because of possible concomitant pancreatic ductal adenocarcinoma): surveillance MAY be discontinued for cysts <20 mm with no morphological change and no worrisome features after 5 years, with consideration of patient condition and life expectancy, and SHOULD be discontinued for patients unfit for surgery or with life expectancy <10 years, but this discontinuation guidance may not apply to younger patients, and cumulative concomitant-PDAC risk continues to accrue (reported 2.2%, 4.6%, 7.4% at 5, 10, 15 years in one Japanese BD-IPMN cohort), so continued surveillance remains a legitimate alternative. After resection of non-invasive IPMN the pancreatic remnant carries increased risk and warrants long-term surveillance as long as the patient remains fit for further intervention (roughly yearly imaging without additional risk factors, every 6 months with higher-risk features); after total pancreatectomy for non-invasive disease, IPMN-specific surveillance may stop if uneventful over 5 years. (Kyoto 2024 addresses IPMN specifically; the 'all presumed MCNs are resected' rule and the family-history/germline CAPS pathway in the current entry come from other guidelines and are not part of this document.)