Biliary endoprostheses. Plastic versus metal stents.

Plastic biliary endoprostheses relieved malignant obstructive jaundice in 80% to 90% of the patients. The comfort of a completely indwelling endoprosthesis should be offered to all palliatively treated tumor patients, and external-internal catheters should be reserved for the minority of patients who return with reoccluded endoprostheses. These patients have bacterial flora that rapidly contaminates the endoprosthesis and causes encrustations and reocclusions. Thus, a second endoprosthesis also would reocclude quickly. The mechanism of reocclusion of plastic and metal endoprostheses is completely different. In plastic endoprostheses, bacterial contamination causes decomposition of the bile and subsequent encrustation. In metal endoprostheses tumor ingrowths between the struts of the stent cause reocclusion. Tumor ingrowths were observed in only 6.5% of metal prostheses with a narrow woven mesh (Wallstent), whereas prostheses with large distances between the struts (Gianturco stent) had ingrowth rates of 19% to 50%. This fact shows that tumor ingrowths can be reduced by narrowing the spaces between the metallic network, and, therefore, improvements in the design of the metal stents should reduce the occlusion rate to or below that of plastic endoprostheses, which currently have a lower encrustation rate. The major advantages of expandable metal prostheses are the relative ease and the minimal trauma of the implantation procedure. The Wallstent endoprosthesis, in particular, can be inserted through a 7-F introducer sheath and offers the chance of single-step placement. The 30-day mortality rate, therefore, was only 5%. This is significantly lower than the 30-day mortality rate after insertion of plastic prostheses (15% to 24%). Even simple external catheter drainage procedures have a higher reported 30-day mortality rate (27%). Expandable metal endoprostheses would be the most useful device if the occlusion rate could be kept under 10% in large series. Increasing the length of the endoprostheses to 10 cm in the expanded state could also improve the long-term patency rates.