Читать книгу Veterinary Surgical Oncology - Группа авторов - Страница 72

Vascular and nonvascular stents have revolutionized the treatment of many human diseases. While stents are commonly used in human medicine to treat coronary artery disease, stents are also used to treat benign and malignant obstructions (Pron et al. 1999; Jamshidi et al. 2008; Lewis 2008; Phillips et al. 2008; Foo et al. 2010). Technological improvements in stents are constantly being made, and stents specific to veterinary needs have been created.

Both self‐expanding and balloon‐expandable stents are available, and the choice of stent is dependent on the intended purpose and location of deployment. Self‐expanding stents have the advantages of being more flexible and easier to navigate through angled or tortuous vessels as compared with balloon‐expandable stents (Valji 2006). Additionally, self‐expanding stents should be used in vessels with variable diameters, as these stents will conform to the changing diameter along that vessel (Valji 2006). Balloon‐expandable stents not only tend to have greater radial force and hoop strength as compared to self‐expanding stents but also may experience collapse after placement (Valji 2006).

Stents are most commonly composed of stainless steel or metal alloys such as nitinol (nickel‐titanium) and elgiloy (cobalt‐chromium) and may have a covering of polyurethane, polyethylene terephthalate, polytetrafluoroethylene, or silicone (Stoeckel et al. 2002; Valji 2006; Jamshidi et al. 2008; Lewis 2008; Hanawa 2009). Ureteral stents are composed of polyethylene, polyurethane, hydrogel, silicone, or thermoplastic polymer and are formed into a tube; metal ureteral stents have also been used (Auge and Preminger 2002; Liatsikos et al. 2009; Venkatesan et al. 2010).

Several different methods are used to fabricate stents. The majority of stents are made from laser cutting (Stoeckel et al. 2002). Other fabrication techniques include photochemical etching, waterjet cutting, braiding, knitting, and coiling (Stoeckel et al. 2002). The interventional radiologist should be familiar with the method used to make each stent as this affects the deployment and eventual configuration of the stent. For instance, braided designs will shorten after expansion, and it is critical to understand this if the appropriate size stent is to be selected (Stoeckel et al. 2002).

Vascular obstructions may require stent placement to restore the vascular lumen. Budd–Chiari syndrome is manifested by hepatic venous outflow obstruction secondary to a myriad of diseases, including malignant neoplasia (Beckett and Olliff 2008). The primary nonvascular regions where stent placement can be beneficial include the biliary tree, esophagus, colon, urethra, ureter, trachea/bronchus, and lacrimal duct (Pron et al. 1999). Malignant obstructions are the primary indications for placement of stents in these locations (Pron et al. 1999).

Recent advances in stent technology have included development of drug‐eluting stents, removable stents, radioactive stents, and absorbable stents. Drug‐eluting stents are used commonly in human medicine, and drugs such as paclitaxel and cisplatin have been embedded into the coating on the stent (Ong and Serruys 2005; Lewis 2008; Chao et al. 2013; Kim et al. 2014). Drug‐eluting stents are most commonly used for cardiovascular disease in humans (Lewis 2008), although clinical cases of hepatobiliary malignancy have been treated with drug‐eluting stents (Suk et al. 2007). Additionally, paclitaxel‐eluting stents have been evaluated in the urinary tracts of pigs and dogs (Shin et al. 2005; Liatsikos et al. 2007). Removable and absorbable stents are being used in human IR (Lootz et al. 2001; Tammela and Talja 2003; Grabow et al. 2005; Lewis 2008; McLoughlin and Byrne 2008; Kotsar et al. 2010); however, the application for removable and absorbable stents in veterinary IO is likely to be limited. Further research is needed to evaluate the use of radioactive stents, but early research and clinical results are hopeful (Liu et al. 2007, 2009). These stents provide an intraluminal source of brachytherapy with the goal of local tumor control (Balter 1998; Liu et al. 2007, 2009).