SAGES Magazine

THE SOUTH AFRICAN GASTROENTEROLOGY REVIEW 2021 | VOLUME 19 | ISSUE 2 | 13 and obstruction. Methods to overcome stent migration include anchoring the stent to the oesophageal wall using through-the- scope (TTS) or over-the-scope (OTS) clips, endoscopic suturing, or utilizing partially covered stents. 18 Partially covered stents have a covered middle but exposed bare metal ends allowing hypertrophic mucosa ingrowth which fixes the stent in place. As patient survival is improving, the fundamental need regarding SEMS is for the stents to be durable and yet easily removable, should the need arise. 16 Depending on the circumstance, larger lumen stents may reduce the risk of migration particularly when placed across the OG junction. Anti-reflux stents Oesophageal squamous cell carcinoma, and increasingly adenocarcinomas affecting the gastroesophageal junction, result in stricture formation and secondary dysphagia. Stents which extend past the oesophagogastric junction result in troublesome acid reflux and passive regurgitation which affect quality of life. This has led to the design of a variety of anti-reflux valves incorporated into the stents to prevent reflux. Figure 4 shows a typical example. They have largely been ineffective clinically and are not recommended for use outside a clinical trial. They may become more important when oncological protocols significantly increase survival if they can be proven to have long-term efficacy. Subsequent to the development of SEMS, other materials have been used in self expanding stents, these include expandable plastic and biodegradable stents. Self-expandable plastic stents (SEPS) Self-expandable plastic stents are manufactured using a polyester mesh. Figure 3 shows an example. To prevent tissue hyperplasia and ingrowth, an inner silicone lining extends throughout the stent and covers both ends. Not surprisingly, the proximal ends of the SEPS are flared in an attempt to overcome stent migration. Although the stents can be placed under direct endoscopic visualisation, fluoroscopic placement is also possible as the stents are impregnated with barium at various points. The major drawback of SEPS is the bulky delivery device diameter which ranges from 12 to 14mm, twice that of SEMS which means that predilatation is mandatory. This coupled with migration rates, as high a 30% when used in malignant disease, has led to a decline in their use in more recent years. 15 Bio-degradable (BD) stents With theexpandinguseof stents inbenigndiseasesaneedhas risen for temporary stents that do not need to be physically removed. Bio-degradable stents are made from polydiaxanone (Figure 4) or poly-L-lactic acid. Degradation usually starts occurring after about 4 to 5 weeks, and by 2 to 3 months the stent would have completely dissolved. The proposed benefit of these stents is in benign disease, where they may decrease the need for repeat Figure 4. Specialised Stents used in specific situations procedures. Stent migration and tissue reactionary ingrowth are problematic as is stent degradation which is temperature and pH dependant. These factors may result in premature collapse of the stent and failure to provide prolonged stricture dilation needed to effect a permanent restoration of adequate luminal patency. 18 This has led to a decline in their use. Future perspectives Drug-eluting self-expandable metal stents (DE- SEMS) In the case of inoperable malignancies, attempts have been made in vitro and in animal models to create drug-eluting SEMS. The SEMS are loaded with a drug-coated polymer coat aimed at providing a mechanical lumen as well as delivering a chemotherapeutic drug. At present many animal studies have shown promising results with docetaxel, paclitaxel, 5- fluorouracil, and gemcitabine. 18 3D-printed stents Lin et al. highlighted the potential for personalizing stents using 3D-printers. They showed that self-expansile, flexible polymer stents of various sizes and shapes could be printed with good results both in-vitro and ex vivo (using a porcine oesophagus). 19 Fouladien et al. subsequently raised the bar further by introducing drug-eluting 3D-printed stents. They were able to demonstrate sustained release of 5-flourouracil in vitro for 110 days. The future aims would be to provide stents that are personalised with patient specific shapes and drug doses. 20 Current indications for oesophageal stenting In the UK in 2017, 10 manufacturers had approximately 35 different oesophageal stents available on the market. The difficulty is deciding on which stent is most appropriate for a specific situation. 16 The following recommendations are in keeping with the current European Society of Gastrointestinal Endoscopy (ESGE) guidelines summarised in Table 1. Malignant disease of the oesophagus and cardia of the stomach At present, oesophageal cancer is the seventh most common cause of cancer worldwide and ranks sixth in cancer-related mortality overall. 21 Management principles in advanced disease with poor short-term survival (less than 3 months) include placement of a SEMS (fully or partially covered) as well as palliative chemoradiotherapy, which has been shown to improve outcomes in locally advanced disease. 22,23 In Africa, however, the outcome is poorer due to late presentation, with more advanced disease and less likelihood of resectability. In Tenkwa Hospital, Kenya,White et al. demonstrated that SEMS alone couldbe utilized for durable palliation of malignant dysphagia. This was done on an ambulatory basis and survival outcomes proved to be substantially longer than reported in studies from resource-rich nations. 24 The concern in South Africa, however, is varied resource allocation amongst different hospitals and provinces, with inequalities in the delivery of healthcare service. Even within tertiary centres there were discrepancies in stent availability, resulting in some hospitals resorting to repeated dilatations as a means of palliating malignant dysphagia. 25 In patients with malignant dysphagia and an expected longer survival, other local treatment modalities have been explored instead of stenting. These include laser therapy, photodynamic therapy and oesophageal bypass. At this stage however, although they have shown comparable outcomes, SEMS remains the preferable modality. The only exception is in the case of brachytherapy, which, if available, may be used as an alternative, or in combination with stenting. 22 It provides a more durable relief of dysphagia and has a lower risk of serious adverse events. 26 REVIEW