This case illustrates a rare delayed presentation of stones at the confluence of the bile and pancreatic ducts following biliary-enteric anastomosis in a patient with pancreaticobiliary duct disease secondary to APBDU. It is widely recognized as a primary etiological factor in pancreaticobiliary disorders, facilitating the reflux and mixing of pancreatic and biliary secretions, which induces epithelial injury and promotes stone formation [5] (Figure 4). In pediatric patients with choledochal cysts, APBDU significantly contributes to protein plug accumulation within the pancreatic duct, often preceding calculi development [8]. Distinct from most previously reported cases, our patient underwent surgical intervention postoperatively. Although the biliary-enteric anastomosis successfully alleviated biliary obstruction, it failed to correct the underlying APBDU, leaving a considerably long distal CBD stump (approximately 2.5 cm). Persistent mixing of pancreatic and biliary fluids, combined with stasis of pancreatic juice within this blind pouch, created a "double-hit" pathogenic mechanism that fostered the formation of large, hard, pancreatic-duct-type stones within the common channel [9]. This pathophysiology fundamentally differs from that of typical postoperative bile duct stones or intrahepatic calculi [10].

Further analysis indicates that, while stone recurrence after choledochojejunostomy is not infrequent, recurrent stones typically localize within the intrahepatic ducts or near the anastomotic site and are predominantly composed of bilirubin or cholesterol [9,11-13]. In contrast, stones forming within the distal bile duct stump, as observed here, can trigger recurrent pancreatitis [9]. In other scenarios, Roux-en-Y choledochojejunostomy is frequently employed as a surgical option for refractory CBD stones following multiple unsuccessful endoscopic retrievals [12]. The present case, however, highlights a delayed complication arising after prior choledochojejunostomy, suggesting that biliary diversion alone cannot fully prevent stone recurrence if APBDU remains uncorrected or if an excessively long blind pouch persists. Consequently, this case broadens the spectrum of APBDU-associated complications and underscores the critical need for comprehensive anatomical assessment and optimization of the initial surgical approach [13].

A key diagnostic challenge lies in the occult nature of APBDU and its potential omission during the primary operation. Clinical manifestations of APBDU are nonspecific and frequently mimic ordinary cholelithiasis or cholangitis, leading clinicians to overlook this condition during diagnosis [14]. Conventional imaging modalities, such as abdominal ultrasound, lack the resolution to delineate the fine anatomy of the pancreaticobiliary junction. Without preoperative high-resolution imaging - particularly MRCP - this crucial anatomical anomaly is easily missed [15]. Therefore, clinicians should routinely screen for APBDU in high-risk populations, including young individuals with unexplained cholelithiasis, patients developing gallstones after biliary surgery, and those suffering from persistent idiopathic pancreatitis [16]. MRCP serves as a noninvasive first-line screening tool capable of visualizing the length of the common channel and relevant anatomical relationships, whereas ERCP functions as both a diagnostic and therapeutic modality [17]. This case demonstrates that endoscopic interventions can be considered a first-line treatment strategy, offering both feasibility and clinical benefit to clinical decision-makers. Despite the substantial size and severe impaction of the calculi, a minimally invasive resolution was accomplished by integrating endoscopic sphincterotomy with intraductal lithotripsy and cholangioscope-guided extraction. These findings further elucidate the utility of endoscopic interventions for complex biliary and pancreatic duct lithiasis. Nevertheless, endoscopic management is not universally indicated. In scenarios involving significant common channel dilation, recurrent stone formation, unsuccessful endoscopic attempts, or suspected malignancy, surgical revision (e.g., revised choledochojejunostomy with common channel plasty) should be considered to rectify the anatomical anomalies driving stone genesis [18]. Practitioners must balance minimally invasive endoscopy against definitive surgery through rigorous imaging evaluation and risk-benefit assessment. In conclusion, this case report juxtaposes clinical data with existing literature to examine the unique pathogenesis, diagnostic challenges, and therapeutic strategies regarding rare, long-term common duct stones following choledochoenterostomy in patients with APBDU. The central tenet is that clinicians must address the underlying etiology rather than merely managing obstructive sequelae. This necessitates preoperative biliary mapping via MRCP and adjunctive modalities, alongside optimized intraoperative techniques to minimize the residual CBD stump and prevent blind pouch formation. Ultimately, lifelong surveillance is imperative for APBDU patients, even postoperatively, to ensure early detection and management of latent long-term risks.

This report acknowledges certain limitations. As a single-center case study, its findings require validation within larger prospective cohorts. Furthermore, the follow-up duration remains brief; while short-term efficacy is evident, long-term hazards such as stone recurrence and delayed complications (including biliary malignancies) warrant continuous monitoring. Future research should establish risk-stratification models incorporating anatomical classifications and surgical variables to tailor postoperative surveillance and interventions. Nonetheless, the insights gained from this case offer valuable guidance for refining the comprehensive management of similar complex cases in clinical practice.