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ENDOPROSTHESES IN GI STENOSES
GEORGE ALEXANDER, GOURDAS CHOUDHURI
Department of Gastroenterology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow.
INTRODUCTION
Endoscopic deployment of stents is a well-established and minimally invasive method for re-establishing luminal patency. There is a wealth of information regarding the use of stents in oesophageal obstruction, but information regarding the clinical outcome when they are used in malignant gastric, duodenal and colonic obstruction is less.
Since 1992, many studies have documented the safety and efficacy of self-expanding metal stents used to palliate patients with malignant gastro-intestinal obstruction who are not fit for surgery. The compressible nature of these prostheses allows insertion via small diameter delivery tubes and potentially allows application in a variety of previously unstentable gastrointestinal stenoses.
TYPES OF STENTS
The main type of stents used today, the self Expanding Metal Stents (SEMS) are composed of a variety of metal alloys and have varying shapes and sizes, depending on the individual manufacturer and organ of placement. The radial expansile forces and degree of shortening differ between Stent types.[1]
SEMS with a covering membrane (covered stents) prevent tumour in-growth through the mesh wall.[2] By the tissue response to the stents, they become incorporated into both the tumour and surrounding tissue by pressure necrosis. This allows anchoring and prevents stent migration.
With use of covered stents, integration does not always occur and a higher rate of migration is seen. Stent embedment accounts also for some adverse effects due to erosion through gastrointestinal wall.
Oesophageal stenting
In oesophageal carcinoma, as the 5 year survival rate after surgery (oesophageal) is only 20-25% and the median survival time after diagnoses is 12-30 months only, 85% of patients are treated palliatively.[3]
Stents
The advantage of metal expanding stents compared to plastic stents with plain wall are now well established.[4,5] There is decreased mortality and morbidity in metal stent group,[4,6] metal stent placement is easier, does not require excessive dilation and are potentially better able to relieve dysphagia due to their large diameter (18-25 mm). Stents made of stainless steel alloys have mechanical memory while those of nitinol alloy expand more slowly due to their thermal memory.
There are 3 types of stent construction:-
-The Gianturco Z stent does not change in length when expanding and does not prevent tumour in-growth.
-Nitinol coil stent shrinks when expanding, but prevents tumour in-growth.
-Narrow meshed knitted stents are more flexible, reduce in length (to 1/3 rd) while expanding and tumour in-growth is less severe.
Coating Z or knitted stents with silicone, polyethylene and Dacron have been proposed but this increases the rate of dislocation and sliding. Tyglon plastic stents have been also used for effective palliation and re-intervention rates are comparable to self-expanding metal stents[7] May et al[8] compared 3 types of prostheses, Wallstents, Ultra flex and Z stents and found comparable improvement in dysphagia. 22%, 37% and 10% respectively required early re-intervention in this study due to displacement or inadequate expansion.
Indication for Stenting
When the general condition of the patient is poor, the procedure is carried out as mono-therapy.
Tumors distal to pharyngo-oesophageal junction are considered as a contraindication to stenting even though it is easier with a metal stent. But here gastrostomy remains a better choice.
Infiltrative tumours require stenting. Laser can be used when proximal or distal end of stent is obstructed by tumour regrowth. Caution is recommended in stenting oesophagus after irradiation as there is increased chance of complications.[9] Thickness of the oesophageal wall must be evaluated by CET or echo-endoscopy.
In case of respiratory fistula, coated metal stents with a Z or knitted mesh structure are used but incomplete sealing still occurs due to initial misplacement, leakage at proximal or distal end or dislocation. In case of large fistula double stenting with oesophageal and tracheal stenting has to be done.
Re-intervention[10]
For proximal tumour overgrowth/ in-growth in upper or middle 1/3 of Oesophagus, repeated stenting, debridement or laser vapourization can be done.
For distal tumour growth at oesophago-gastric junction, 2nd stent can be put.
Stenting in Gastric outlet obstruction
Stents
The main types of SEMS used are Enteral Wallstent[11] and Gianturco-Z stent,[12] although practically any SEMS with an adequate luminal diameter may be utilized.[13]
The advantage of enteral Wallstent is that the delivery system is much longer, which is important, as the gastric lumen leads to looping of the system along the greater curve,[14] also it has a small diameter delivery system (10-Fr) allowing passage directly through the working channel of a therapeutic endoscope.
The disadvantage is that, it is not available in covered version and so is susceptible to obstruction by tumour regrowth.
Prior to placing the SEMS, it is advisable to obtain a radiographic contrast study to assess the anatomy, length of stricture, degree of obstruction and also to rule out other multiple sites of obstruction. For lesions distal to second part of duodenum, colonoscope can be used.
Procedure
The procedure is done in a room with fluoroscopy. Patient should be in left lateral decubitus or prone position. If endoscope can be passed through obstruction easily, this should be attempted; even though it is not essential.
If a stent is chosen that will pass through the endoscopy channel, procedure is as for placement of biliary stent. If not, the stent is loaded over guide wire under fluoroscopic guidance. The stent should be 3-4 cm longer than the obstruction.
If endoscope does not pass through the lesion, biliary guide wire and biliary catheter is used to traverse the obstruction. Once stent is deployed, under fluoroscopy, fanning of both ends should be seen and contrast can be injected to assess patency.
Limitations and success rate
Technical success rate in centres of experience range from 90-100%.[11,13,14,18] Clinical success rate, defined as the ability to adequately maintain hydration and nutritional status is achieved in 80-90%.[13,11,14] Kim S H et al[14] found quality of life improved in 78% of patients, in whom these were placed.
Limitations include inability to pass a guide wire through the stricture, anatomic difficulties or complicated post surgery anatomy. Most patients will not be able to tolerate solid food immediately and are advised to advance from liquids to solids slowly, avoiding green leafy vegetables, which can lead to occlusion.
Regarding patency Yates l et al[13] found 78% patency at 200 days for Wallstent and that of Gianturco-Z stents was 6 months when used in oesophagus and 1 year when used in the biliary tree.[12] Restenosis rates of 8-46% at interval of 2-21 weeks have been reported.[11,16,13,17] Yim et al[18] compared endoscopic enteral Wallstent with palliative surgery for malignant upper gastrointestinal obstruction and found that stenting is a safe, efficacious and cost-effective procedure with good clinical outcome, lower charges and shorter hospitalization than the surgical alternative.
Complications and safety
Intra-procedural complications associated with sedation, pulmonary aspiration, stent malposition, perforation and bleeding may occur. Late complications include distal stent migration[2,11] (more with covered stents),[2] bleeding, perforation as well as fistula formation.
Stent migration may be asymptomatic or result in bleeding, obstruction or perforation. Symptomatic Stent occlusion requires intervention. SEMS may produce imaging artifacts in CT and MRI.
Indications
Advanced carcinoma of pancreatic head is the most common malignancy causing gastric outlet obstruction,[18] although primary or recurrent gastric carcinoma or metastatic disease to duodenum or jejunum may also result in gastric outlet obstruction.[18]
Co-existent biliary occlusion is commonly present in malignant duodenal obstruction and an expandable biliary stent should be placed prior to duodenal stenting in patients with known or impending biliary obstruction.
The indications for stenting in upper GIT are symptoms of gastric outlet obstruction (GOO) in patients with unresectable disease or poor functional status due to advanced age and co-morbid medical conditions.
Colorectal Stenting
In the colon, the procedure was initially employed in cases of acute intestinal obstruction caused by malignant neoplasms, to open the blockage and allow the colon to empty, thereby avoiding need for urgent surgical intervention with its high morbidity and mortality rate.[23] The procedure also proved useful in preparing the intestine and improving patient condition for elective surgery, which carries a lower risk and a better chance of successful primary anastomoses.[24,25]
Additionally, stent implanting constitutes a definitive primary palliative treatment in patients with metastatic disease or in patients who are not candidates for surgery.[25,26,20] The devices used include nonexpandable plastic stent[26] and expandable metal stents from nitinol mesh or stainless steel.[20-22]
Uncovered metal stents have been successfully used pre-op and in palliation[21,22] with stents occlusion rates of 10-30%,[20,28] Also covered stents have been used for palliation of recto-sigmoid cancer[20] with early and late complications of 22% and 3%, respectively.
CONCLUSIONS
With improvements in assessing tumour resectability using abdominal imaging fewer patients are undergoing surgical exploration and thus palliative surgery. Thus endoscopic palliation may be playing an increasing role. The decision to proceed with stent placement or surgery should be made on individual basis until multicentric randomized trials demonstrate the optimal treatment strategies.
REFERENCES
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