Histopathologic characteristics of choledochal cysts and their clinical implications have not been previously comprehensively studied.
Smooth muscle distribution patterns and other histologic findings (inflammation, metaplasia, dysplasia, and heterotopia) in 233 surgically resected choledochal cysts were evaluated.
Mean patient age was 23.3 ± 19.8 years, with male:female ratio of 0.3. Most cases were Todani type I (175 cases, 75.1%) or IVa (56 cases, 24.1%). Choledochal cysts with thin scattered/no muscle fiber (175 cases, 75.1%) were the predominant pattern and were associated with more frequent postoperative biliary stricture (P = .031), less frequent pyloric metaplasia (P = .016), and mucosal smooth muscle aggregates (P < .001) compared to cysts with thick muscle bundles. Severe chronic cholangitis (P = .049), pyloric metaplasia (P = .019), mucosal smooth muscle aggregates (P < .001), biliary intraepithelial neoplasia (P = .021), and associated bile duct (P = .021) and gallbladder carcinomas (P = .03) were more common in adults (age >20 years vs ≤20 years), suggesting that chronic irritation in association with developmental anomalies involves tumorigenesis from choledochal cysts.
Smooth muscle distribution pattern of choledochal cyst may predict postoperative complication, raising clinical implications of smooth muscle patterns in postoperative management of choledochal cysts.

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