Introduction:
Preoperative biliary drainage has been widely used to treat patients with malignant biliary obstruction. However, it is still unclear which method is more effective: internal drainage or external drainage. Thus, we carried out a meta-analysis to compare the safety and efficacy of the two drainage methods in treatment of malignant biliary obstruction in terms of preoperative and postoperative complications.

Material and methods:
We conducted a literature search of Medline, EMBASE, PubMed, Ovid journals and the Cochrane Library, and compared internal drainage and external drainage in malignant biliary obstruction patients. The pre- and postoperative complications, stent dysfunction rate and mortality were analyzed.

Results:
Ten published studies (n = 1464 patients) were included in this meta-analysis. We found that patients with malignant biliary obstruction who received external drainage showed reductions in the preoperative cholangitis rate (OR = 0.33, 95% CI: 0.24–0.44, p < 0.00001), the incidence of stent dysfunction (OR = 0.41, 95% CI: 0.30–0.57, p < 0.00001), and total morbidity (OR = 0.34, 95% CI: 0.23–0.50, p < 0.00001) compared with patients who received internal drainage.

Conclusions:
The current meta-analysis indicates that external drainage is better than internal drainage for malignant biliary obstruction in terms of the preoperative cholangitis rate, the incidence of stent dysfunction and total morbidity, etc. However, the findings need to be confirmed by randomized controlled trials.