Initial Biliary Drainage in Unresectable Bismuth Type III Malignant Hilar Obstruction: Comparative Effectiveness of ERCP and PTBD According to Drainage Adequacy in a Retrospective Two-Center Study

Background: Optimal biliary drainage in unresectable malignant hilar obstruction remains challenging, particularly in Bismuth type III disease due to complex biliary anatomy. Emerging evidence suggests that the adequacy of biliary decompression may be more important than the drainage modality itself in determining clinical outcomes. Aim: To compare the effectiveness of endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic biliary drainage (PTBD) in unresectable Bismuth type III malignant hilar obstruction, with particular emphasis on drainage adequacy. Methods: This retrospective two-center study included 199 patients with unresectable Bismuth type III malignant hilar obstruction (ERCP: n = 102; PTBD: n = 97). Drainage adequacy was defined as decompression of at least 50% of the non-atrophic liver using a segment-based anatomical approach. Bilirubin response was evaluated at predefined time points (days 7, 14, and 28). The primary outcome was biochemical response, while secondary outcomes included reintervention, complications, hospital stay, receipt of systemic therapy, and mortality. Results: Baseline characteristics were comparable between groups (mean age 66.8 ± 11.2 vs. 68.4 ± 10.7 years, p = 0.412; male sex 58.3% vs. 61.5%, p = 0.721). PTBD achieved significantly higher rates of adequate drainage than ERCP (p = 0.006). Although biochemical response rates were numerically higher in the PTBD group, multivariable analysis identified drainage adequacy—rather than drainage modality—as the strongest independent predictor of treatment success. Reintervention rates were significantly higher and time to reintervention significantly shorter in the ERCP group (p < 0.001). Cholangitis and post-procedural pain scores were more frequent following PTBD, whereas post-ERCP pancreatitis occurred exclusively after ERCP. No significant differences were observed in 30-day or 1-year mortality between groups. Conclusions: In unresectable Bismuth type III malignant hilar obstruction, drainage adequacy appears to be the principal determinant of clinical success. Although PTBD more frequently achieves adequate biliary decompression, outcomes seem to depend primarily on the effectiveness of drainage rather than the drainage modality itself.