Original articles Development and Implementation of a New Nitinol Stent Design for Managing Benign Stenoses and Fistulas of the Digestive Tract Rodrigo Castaño, MD,1 Oscar Álvarez, MD,2 Jorge Lopera,3 Mario H. Ruiz, MD,4 Andrés Rojas, MD,5 Alejandra Álvarez,6 Luis Miguel Ruiz,6 David Restrepo.7 1 Gastrointestinal Surgery and Endoscopy. Abstract Chief of Postgraduate General Surgery (UPB), Gastrohepatology Group at the University of Background: Benign stenoses, digestive tract ruptures and fistulas are conditions that endanger life and Antioquia, Institute of Clinical Oncology of the are often treated surgically. Recently, the placement of partially or fully covered metal stents has emerged Americas in Medellin, Colombia. rcastanoll@ as a minimally invasive treatment option. This article looks at a new design for stents to determine its clinical hotmail.com 2 Gastroenterologist at Texas Valley Coastal Bend effectiveness. The new stent is a completely covered nitinol stent for treatment of gastrointestinal perforations Veterans Administration Hospital and Clinical Assistant and anastomotic leaks. This article places special emphasis on evaluating reactive hyperplasia. Professor at the University of Texas Health Science Methods: Fifteen had the new completely covered self-expanding nitinol stent placed for treatment of Center at San Antonio in San Antonio, Texas USA 3 Interventional Radiologist at the University of Texas benign esophageal perforations, anastomotic leaks, and stenoses following upper or lower gastrointestinal in the United States. surgery during 2012 and 2013. The stents are 20 mm in diameter in the middle and 28 mm in diameter at the 4 General Surgeon at the Hospital Pablo Tobón Uribe in proximal end. Information about patient demographics, type of lesion, lesion locations, stent removal, clinical Medellin, Colombia 5 General Surgeon, Clinic Cancerology Institute Las success and complications was collected. Americas. Medellin, Colombia Results: A total of 15 stents were placed in 15 patients to treat anastomotic leaks (n = 8), esophageal 5 Undergraduate Students in the Faculty of Medicine stenoses (n = 2), colorectal stenoses (n = 2), a gastrojejunostomy stenosis (n = 1), an esophageal iatrogenic at the Universidad Pontificia Bolivariana in Medellin, rupture (n = 1), and a pyloric stenosis (n = 1). Endoscopic removal of the stent was successful in all patients. Colombia 6 Undergraduate Student in the Faculty of Medicine at Although it was particularly difficult in one case because of reactive hyperplasia. Clinical success was achie- CES in Medellin, Colombia ved in nine patients (73%). Average duration of time between stent placement and removal was 10 weeks with a range of 7 to 12 weeks. In total, seven complications occurred in 15 patients (47%): reactive hyperplasia (n ......................................... Received: 19-08-14 = 1), migration (n = 3) severe pain (n = 2) esophageal ulceration (n = 1) only one patient required surgery after Accepted: 21-07-15 stent failure. No patients died as the result of stenting. Conclusions: A redesigned completely covered stent kept in place for 10 weeks may be an alternative to surgery for treating gastrointestinal perforations, anastomotic stenoses and fistulas. The efficacy of the new stent differs from that of conventional stents. The choice depends on the expected risks of stent migration and reactive hyperplasia. Keywords Metal stent, nitinol, benign stenosis, gastrointestinal fistula, esophageal perforation. INTRODUCTION risks inherent in the use of rigid plastic stents in the GI and biliary tracts (1, 2). Stents have been used for many decades for palliation of Today, there is no doubt about the benefits of stents for obstruction in different segments of the biliary tract and palliative treatment of malignant strictures of the GI tract gastrointestinal (GI) tract. Their usage has boomed since including in critical situations with high risks of morbidity the recent introduction of self-expanding metal stents and mortality such as esophageal-respiratory fistulas (3-5). (SEMS) which have largely eliminated the discomforts and Self-expanding metal stents have even replaced various © 2015 Asociaciones Colombianas de Gastroenterología, Endoscopia digestiva, Coloproctología y Hepatología 260 surgical procedures that had been regarded as standard tions (22, 23). The mechanism of action of these stents is to palliation for these patients (6, 7). In addition, their use seal and thereby close the fistula, but some studies and the now extends to other benign diseases both in the biliary guidelines of the American College of Gastroenterologists tree and in the GI tract (8-11). Surgical interventions had have concluded that the quality of evidence for the use of been considered the “gold standard” of treatment of these metallic stents for perforations and leakage is low and that lesions (12-14), but while surgery improves survival rates, the level of evidence for recommendation is weak (24, 25). it is still associated with high mortality rates (30%) mainly The purpose of this study is to show the development related to late diagnosis (15). and clinical implementation of a new nitinol stent design. Metal stents have not been widely used to treat benign This new design is based on the original model of esopha- strictures of the GI tract for several reasons. First, most geal stent designed by Song but rather than being designed metallic stents cannot be removed without surgery and the- for conventional situations such as palliation of tumors, it refore cannot be used temporarily. Second, the long-term is designed for benign pathologies such as cases of stenoses, implications of a permanent metallic stent in the GI tract is leakage and perforations. The intention is to offer non-sur- unknown. Third, experiences in animal models and in some gical management of these disorders since surgery in these of our patients with benign obstructions have shown that in cases may result in high risks of morbidity and mortality. some cases mucosal hyperplasia may eventually occlude the stent. Fourth, for patients who are in good general condition, NEW CONCEPTS FOR BIOMECHANICAL NITINOL surgery is justified (16). Finally, there is no design or model STENTS of stent proposed for the management of benign situations. To date, there have been few reports about the use of The History of Nitinol metallic stents for treatment of benign conditions, and most of those have described significant rates of complications In 1959, William Beuhler discovered a 55% nickel (Ni) resulting from the stent itself and from removal of the stent. and 45% titanium (Ti) alloy while working in the laborato- The most frequent complication is migration, next frequent ries of the US Naval Ordnance Laboratory. The new alloy is formation of a new stenosis, followed by pain at the site of was given the name Nitinol which is an acronym for its stent placement and then by specific situations such as faci- ingredients and the place where it was discovered (Nickel litation of GERD. Proximal and distal migrations are more Titanium Naval Ordnance Laboratory) (26). This mate- common with fully covered stents while stenoses are most rial is now known as the memory metal because two of its frequently observed stents that are uncovered either at the important properties are shape memory and superelasti- ends or in the center to allow for tissue growth between the city (27). Both of these properties are important for both interstices of the fabric of stent (17). gastrointestinal stents. Nevertheless, various reports suggest that the temporary use of self-expanding metal stents may be a reasonable Fluoroscopic Features option for patients with benign GI tract stenoses, fistulas or perforations (18-20). Song has found that esophageal Nitinol has come to displace other metals such as steel and stenoses recurred in three of four patients in whom stents elgiloy that had been used in the manufacture of stents in migrated within the first two months after placement, but part because it offers better contrast in fluoroscopic evalua- that there were no recurrences of stenoses among patients tions than do other materials. In tests run with the newly whose stents migrated or were removed more than two designed stent, it demonstrated contrast levels comparable months after placement (21). For this reason, and because to those of other stents (Figure 1). formation of a distal or proximal stenosis is rare during this period, Song has proposed that stents be kept in place for Biomedical Properties no less than eight weeks for management of benign strictu- res in not less than eight weeks esophagus. Like other metals, nitinol, undergoes phase transitions The same stents that have traditionally been used for between the face-centered cubic (FCC) configuration of management of malignant strictures have been used for gamma iron crystal structures (Austenite, the most common benign strictures even though they do not necessarily offer form of stainless steel) and a body-centered tetragonal form the tightest fit or the least likelihood of migration. They are (Martensite, alloys which have austenitic structure at high also used for less common situations which have low rates temperatures). At room temperature the nitinol is in its mar- of morbidity and mortality and which are not necessarily tensite phase which is soft and easily deformed. It has shape stenoses. These include situations such as gastrointestinal memory which is the effect of something that