Uncovered stent

Delayed endothelial healing. In case 1, a smooth, white lesion was detected at three and nine months. In case 2, erosion with a superficial thrombus was seen at three months. At nine months, the erosion had disappeared, although an uncovered stent was observed. In case 3, severe, circumferential erosion with superficial thrombus was detected at three months, with erosion still evident but partly improved at nine months. These results suggest that the healing process was not completed nine months after brachytherapy. Source From Ref. 73. 

The covered stent has a layer of polyurethane on the outside of the mesh of the stent Similar to the Wallstent, the covered design has uncovered portions at either end. The covered stents are available in 17-mm and 22-mm diameter versions (unflared portions), and the uncovered stents are available in 18-mm and 23-mm diameter designs. The stents are available in the following lengths 7 cm (uncovered version only), 10 cm, 12 cm, and 15 cm. The dehvery system is 16.5-F diameter. 

As uncovered stents are prone to ingrowth of tumor, covered endoprostheses should be used whenever possible. The choice of stent depends to some extent... 

The ideal stent would be resistant to tumor ingrowth and migration. Researchers have been trying for some years to produce an uncovered stent with a coating material on the metallic mesh that would resist tumor ingrowth. Such a stent would have the optimal properties of covered stents (i.e., no tumor ingrowth) and uncovered stents (i.e., no migration). 

Fig. 3.1a-c. Uncovered and covered oesophageal Wallstents. a Uncovered stent, b Covered stent with slightly flared ends, c Covered stent with conic shape (Flamingo)... 

Very recently four larger series totalling 119 patients with gastroduodenal obstruction treated with uncovered stents were published by Pinto et al. (2001), Yim et al. (2001), Razzaq et al. (2001) and Adler and Baron (2000a) (Table 3.1). 

Tumour in- or overgrowth, though a possible and expected cause of reobstruction, was not seen in our patients and has been reported in less than 17% of previous smaller series with uncovered stents (Pinto 1997 SOETIKNO et al. 1998 Feretis et al. 1996). In the review of 91 patients collected by Mauro et al. (2000) only 14 cases of tumour obstruction (15%) were seen. This is probably due to the fact that most obstructions were by external tumour compression or the survival was often limited to 6 months or less. In the four most recent larger series comprising 23-36 patients, and totalling 119 patients (Table 3.1),... 

Several cases of successful treatment of coloen-teral or colovesical fistulae have been reported. Apart from one author using an uncovered stent (Cwikiel and Andren-Sandberg 1993), all other investigators applied covered stents to seal the fistula (Choo et aL 1998 Repici et al. 2000 Lobato et al. 1999b Grunshaw and Ball 2001). 

There are no dedicated tracheobronchial covered balloon-expandable stents available yet. The Gianturco stent for tracheobronchial application is commercially only provided as an uncovered stent. 

This chapter focuses on the insertion technique for metallic covered and uncovered stents. For placement of plastic tube stents (like the Montgomery, Dumon, or Dynamic Stent) special introductory systems and rigid bronchoscopy are required. These stents are usually placed by experienced interventional bron-choscopists. The interested reader might refer to one of the review articles on interventional bronchoscopy (SoNETT et al. 1995 Beamis and Mathur 1999 Mehta and Dasgupta 1999 Wood 2001). 

Similar results were obtained fi-om two other groups also using Gianturco-type stents (Tojo et al. 1996 ZwiscHENBERGER et al. 1997). Mainly uncovered stents were placed for mahgnant strictures in a total of 37 patients. Stent placement was technically successful in all cases and resulted in significant improvement of the dyspnea scores. 

A recent study reported on the placement of 28 Ultraflex stents in 25 patients with respiratory distress due to inoperable airway obstruction (Madden et al. 2002). In this trial, 21 tracheal and seven bronchial stents were placed. The vast majority of patients received covered stents (n=21), the minority uncovered stents (n=7). Of the 25 patients, 20 reported symptomatic improvement after stent implantation. The follow-up period ranged from 3 days to 27 months. Late complications included sputum retention and infection in four patients, halitosis in one patient, and granulation tissue formation in another patient. 

Metalhc stents can induce granuloma formation, which might be excessive, particularly in benign strictures. A complication of uncovered stents is tumor growth through the open mesh. In addition, function of covered stents can be impaired by tumor overgrowth at the proximal and distal margins. 

In the Japanese multicenter trial of the uncovered Ultraflex stent (Miyazawa et al. 2000), tumor ingrowth (24%) and tumor overgrowth (21%) were the most frequent complications during the 2-month follow up period. Mucus retention was noted in 9% and granuloma formation was seen in 3%. No migrations of the uncovered stents occurred. 

Standard uncovered stents can occasionally be used to seal a vascular defect [21] (Fig. 7.6). While it seems counterintuitive that a bare stent would seal an arterial leak, this can work if the defect runs obliquely through the arterial wall. In this setting. 

Fig. 7.6. a Hepatic arteriogram in a patient who developed bleeding several days after a Whipple operation. A pseudoaneurysm (arrow) is seen where the gastroduodenal artery was resected, b A balloon occlusion catheter (arrow) was inflated across the arterial defect to tamponade bleeding until a decision was made regarding deflnitive therapy, c A bare balloon expandable stent (arrows) was placed across the arterial defect with plans to pass microcoils through the stent however, this post-stent study showed that the arterial defect had been sealed by the uncovered stent alone... 

With the advent of these improvements, it is almost certain that constructive endovascular approaches, without adjuvant embolization, will become the treatment of choice for repairing both the common and internal carotid arteries affected by CBS. We predict that the use of such devices will not only substantially diminish the immediate perioperative complications, but also decrease the rate of rCBS attributable to treatment failure that has remained a problem with uncovered stents. 

Historically, first attempts at duodenal stenting were performed with oesophageal stents inserted through a gastrostomy (Razzaq et al. 2001). On the whole the use of softer uncovered stents has become standard practice in the stomach and particularly in the duodenum. Covered stents have proved to have an unacceptably high migration rate and flexibility is of increased importance in order for the stent to conform to the flexures of the small bowel. 

A range of dedicated partially covered and uncovered stents, as well as specialised double stents, have been developed (Song et al. 2004b) and are available on delivery systems for either fluoroscopic or endoscopic placement. 

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