Mechanism of Fibrotic Anastomosis Formation in Endoscopic Ultrasound‐guided Hepaticogastrostomy Using a Plastic Stent: Insights From an Autopsy Case of Perihilar Cholangiocarcinoma

ABSTRACT Endoscopic ultrasound‐guided hepaticogastrostomy (EUS‐HGS) is an established alternative to other biliary drainage techniques for treating malignant biliary obstruction. Although the anastomosis created by EUS‐HGS is believed to mature within several weeks, histopathological evidence supporting this assumption remains limited, particularly in procedures using plastic stents. Here, we report a case of perihilar cholangiocarcinoma in which an endosonographically created route (ESCR) formed by EUS‐HGS using a plastic stent was histologically evaluated at autopsy. An 83‐year‐old man underwent EUS‐HGS with a 7‐Fr plastic stent for recurrent biliary obstruction after duodenal stenosis, which made endoscopic retrograde cholangiography infeasible. The patient died of disease progression 141 days after the initial EUS‐HGS, and an autopsy was performed. Macroscopic evaluation revealed adhesions between the liver and stomach at the ESCR site. Masson's trichrome staining revealed a well‐defined concentric fibrotic tunnel surrounding the stent tract, with fibrotic thickness comparable to the stent diameter. Fibrotic changes varied across tissue layers, being minimal at the mucosal penetration site and most pronounced at the subserosal and serosal levels. Previous reports of EUS‐guided biliary drainage with self‐expandable metallic stents suggest that radial force contributes to anastomosis maturation. In contrast, the present case demonstrates that a robust fibrotic ESCR can develop even after EUS‐HGS with a plastic stent lacking sustained radial force. These findings provide pathological evidence for structural stabilization of ESCR and support the structural basis for trans‐ESCR procedures.