What causes the chain of lakes sign on MRCP and ERCP?
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Answer:
The chain of lakes sign is the appearance of the main pancreatic duct in chronic pancreatitis: alternating segments of dilatation and stricture along its length, so the duct resembles a series of connected lakes rather than a smoothly tapering channel. It is accompanied by dilated and clubbed side branches, intraductal calculi, parenchymal calcification and gland atrophy, and it forms part of the Cambridge classification of ductal changes originally described for ERCP and now applied to MRCP. Secretin-enhanced MRCP improves depiction of the duct and side branches and adds a functional assessment of exocrine reserve. The critical differential is a main-duct intraductal papillary mucinous neoplasm, which also dilates the duct but usually does so more uniformly, with a bulging patulous papilla, mucin, and enhancing mural nodules, and which carries a high risk of malignancy. Equally important is that chronic pancreatitis and pancreatic ductal adenocarcinoma coexist and mimic one another: an abrupt duct cut-off with an atrophic upstream gland, a focal mass, vascular encasement and the double duct sign favour tumour, and where doubt persists, endoscopic ultrasound with biopsy is required. Autoimmune pancreatitis is a further mimic, showing a diffusely narrowed rather than dilated duct with a sausage-shaped gland and a capsule-like rim.
Why is it called so?
The alternating dilated pools and narrow connecting segments look like a chain of lakes joined by streams.
Pathophysiology
In chronic pancreatitis, repeated inflammation causes protein plugs to precipitate within the ducts; these calcify, obstruct side branches and the main duct, and provoke periductal fibrosis. Fibrous contraction produces focal strictures, while the segments between them dilate under the pressure of obstructed exocrine secretion, so the duct develops an irregular beaded contour. Continued acinar destruction and replacement by fibrous tissue cause the gland to atrophy and lose function, giving exocrine insufficiency and later endocrine failure. Alcohol and smoking are the dominant causes in adults, with genetic causes such as PRSS1, SPINK1 and CFTR variants, hypertriglyceridaemia, obstruction and autoimmune disease accounting for much of the remainder.
Alternative names: Chain of lakes; beaded pancreatic duct
Other associated named signs: Double duct sign of a pancreatic head mass and the sausage-shaped pancreas of autoimmune pancreatitis
References
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