Therapeutic Endoscopic Ultrasound

By Peter Vilmann and Manoop S. Bhutani

This book provides  an up-to-date review of therapeutic EUS with an equal focus on technical descriptions with ample endoscopic images/video clips by world experts and the scientific evidence behind the described techniques. The book  provides an overview of the field in a structured manner, starting with general topics on equipment and service development and extending to the fields of EUS-guided drainage, anti-tumor therapies, and other specific EUS-guided interventional treatments. 
Therapeutic Endoscopic Ultrasound is a key resource for endoscopists, gastroenterologists, surgeons, and GI oncologists. 

• Language: English
• Publisher: Springer
• Release date: Jan 7, 2020
• ISBN: 9783030289645

Book preview

© Springer Nature Switzerland AG 2020

E. Kalaitzakis et al. (eds.)Therapeutic Endoscopic Ultrasoundhttps://doi.org/10.1007/978-3-030-28964-5_1

1. Equipment and Accessories for Therapeutic Endoscopic Ultrasound

Mihai Rimbaș¹   and Alberto Larghi²  

(1)

Gastroenterology Department, Colentina Clinical Hospital, Carol Davila University of Medicine, Bucharest, Romania

(2)

Digestive Endoscopy Unit, Fondazione Policlinico Universitario A. Gemelli, IRCCS, Rome, Italy

Mihai Rimbaș

Email: [e-mail]

Alberto Larghi (Corresponding author)

Electronic Supplementary Material

The online version of this chapter (https://​doi.​org/​10.​1007/​978-3-030-28964-5_​1) contains supplementary material, which is available to authorized users.

Keywords

Endoscopic ultrasoundInterventional EUSTherapeutic EUSEchoendoscopesUltrasound processorsEUS accessoriesTumor ablationLumen-apposing metal stentBi-flanged metal stentHepatico-gastrostomyCholedochoduodenostomyPancreatic fluid collection drainageGallbladder drainageIntratumoral injectionIntratumoral implantationEUS fiducials

Key Points

The available therapeutic echoendoscopes have a working channel with a diameter ranging from 3.7 to 4.0 mm, which allows passage of standard and dedicated accessories to perform interventional procedures.

Transluminal access for drainage procedures and/or anastomosis formation is most commonly obtained with standard 19-gauge FNA needles, together with guidewires and mechanical or diathermic devices for tract dilation

Transmural drainage has been obtained with placement of catheter drains, and of either biliary plastic polymer stents or self-expandable metal stents (SEMSs), which have now been largely substituted by the use of specifically designed lumen-apposing or bi-flanged fully covered self-expandable metal stents

Direct transmural access without prior needle puncture and tract dilation is possible with the novel electrocautery-enhanced lumen-apposing stent delivery system

Regular or dedicated needles are available for EUS-guided intratumoral drug injection/implantation, brachytherapy, and fiducial placement

EUS dedicated accessories to achieve EUS-guided tumoral ablation allow the performance of laser therapy, radio-frequency ablation, cryothermal ablation, and photodynamic therapy

Introduction

In the last decades, endoscopic ultrasound (EUS) has rapidly evolved from a purely diagnostic procedure into a more interventional/therapeutic one. This transformation has been driven by the availability of echoendoscopes with large working channels, allowing the passage not only of needles for tissue acquisition, but also of bigger accessories needed to perform more advanced procedures. Although most of the tools and some of the techniques are still in development, numerous advancements have been made in different procedures, such as EUS-guided drainage of pancreatic fluid collections, of bile and pancreatic ducts, and of the gallbladder and in the creation of gastrointestinal (GI) anastomoses and treatment of GI bleeding . Moreover, accessories to perform EUS-guided loco-regional therapies mainly for pancreatic tumors, such as radio-frequency ablation , laser therapy , tumor injection and implantation have been developed and tested in human studies. All these EUS-guided interventions represent potentially the least invasive and most efficacious therapeutic alternatives to more demolitive surgeries. However, one should keep in mind that technological advancements do not automatically mean favourable treatment outcomes, and procedural safety and success mostly depend on proper patient selection, operator’s skills and expertise, organization of the endoscopic unit, and availability of emergency interventional radiological and surgical support.

This chapter describes current and emerging equipment and accessories that are available for therapeutic EUS.

Equipment

Linear Echoendoscopes

Interventional/therapeutic EUS procedures are performed using therapeutic curved linear array (CLA) instruments, which have an oblique endoscopic view, a 5- to 12-MHz ultrasound acoustic frequency, and a 3.7- or 3.8-mm working channel diameter. The CLA echoendoscopes scan in the same longitudinal plane as devices exiting the working channel, enabling their sonographic real-time visualization and guidance during the entire procedure. Trajectory changes of the accessories can be obtained, when needed, by the use of the elevator that determines a downward movement of the device in the ultrasonography image plane. All modern CLA echoendoscopes are electronic, allowing various forms of Doppler sonography to aid in the identification of vascular structures. Curved linear array echoendoscopes featuring all the above characteristics are available from all three major manufacturers (Olympus Medical Corporation Europe, Hamburg, Germany; Pentax Medical Europe, Hamburg, Germany; Fujifilm Medical Systems Europe, Dusseldorf, Germany) (Figs. 1.1, 1.2, and 1.3) with minor differences in scope design and technical specifications, such as shape of the transducers, maneuverability and feel of the instrument (see Table 1.1). However, each of the producers incorporated proprietary features, resulting in differences in the ultrasound image produced, and in the field of ultrasonic view, which ranges between 120° and 180°. In general, the Olympus transducer has a more contoured, rounded tip, allowing for better imaging of structures anterior to the echoendoscope. Pentax linear echoendoscopes incorporate a Hi-Compound feature, which combines frequency and spatial compounding, allowing an image to be scanned from multiple angles.

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Fig. 1.1

Olympus GF-UCT180 Curved Linear Array echoendoscope (image courtesy of Olympus Medical Europe, Hamburg, Germany)

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Fig. 1.2

Pentax EG-3870UTK Curved Linear Array echoendoscope (image courtesy of Pentax Medical Europe, Hamburg, Germany)

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Fig. 1.3

Fujifilm EG-580UT Ultrasonic Convex Scanning Endoscope (image courtesy of Fujifilm Europe, Dusseldorf, Germany)

Table 1.1

Available therapeutic linear array echoendoscopes

Recently, Olympus Medical Corporation has developed the forward-viewing echoendoscope (FV-EUS) with a completely different design (Fig. 1.4). This scope is substantially characterized by a change of orientation in the endoscopic and ultrasonographic views from oblique to forward. This change could lead to some advantages, primarily during interventional procedures, allowing the output of accessories parallel to the longitudinal axis of the endoscope, so as to exert all the force on the tip of the accessory itself, making the procedure theoretically technically easier [1, 2]. Moreover, even if the EUS scanning angle has been substantially reduced from 180° to 90°, the change in the orientation and in the design of the tip allows the inspection of areas of the GI tract that are difficult to be accessed with the CLA instruments [3–6]. However, this scope lacks an elevator to assist in device trajectory adjustment and to guarantee guidewire stability during exchange of accessories, a task highly needed in therapeutic procedures.

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Fig. 1.4

Olympus TGF-UC180J Forward-Viewing linear array echoendoscope (image courtesy of Olympus Medical Europe, Hamburg, Germany)

Another novel development is the new PENTAX EG38-J10UT echoendoscope with increased maneuverability, shorter rigid distal end, rounded tip, as well as powerful angulation (Fig. 1.5). This echoendoscope is also equipped with an enlarged ultrasound scan angle of 150° (compared to the previous one of 120°) and an enlarged working channel of 4.0 mm, with only minor increase in the size of the insertion tube, which allows passage of accessories up to 12 Fr.

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Fig. 1.5

The new EG38-J10UT echoendoscope from Pentax featuring a rounded transducer tip and a large 4-mm working channel, which can accommodate accessories of up to 12 Fr (image courtesy from Marc Giovannini MD)

Ultrasound Processors

Each echoendoscope requires a specific ultrasound processor for ultrasonic imaging. Table 1.1 summarizes the processors compatible with each of the different echoendoscopes. The different producers engineered features and enhancements to the designs of the ultrasound processors that are unique. Fujifilm has developed integration of ZONE Sonography and Sound Speed Correction technologies translated into a better quality of the ultrasonic image. With the new compact Sonart Su-1 processor, fundamental imaging is obtained at 5, 7.5, 10, and 12 MHz, with tissue harmonic imaging at 8 and 10 MHz. Compound harmonic imaging, sound speed imaging and elastography are added features (Fig. 1.6).

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Fig. 1.6

Fujifilm SU-1 Ultrasonic Processor (image courtesy of Fujifilm Europe, Dusseldorf, Germany)

For the Pentax scopes, the Hitachi Ultrasound platform offers fundamental imaging frequencies of 5, 6, 7.5, 9, and 10 MHz. The HI VISION Preirus ultrasound platform combines Hi-Compound with Hi-Resolution imaging, translated into enhanced visualization of boundaries between different structures and reduced angle-dependent artifacts. The therapeutic echoendoscope EG-3870UTK and the newly developed EG38-J10UT are also compatible with the Hitachi ultrasound processors Ascendus, Preirus, Avius, Noblus and the ARIETTA V60 and V70 (Fig. 1.7).

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Fig. 1.7

ARIETTA V70 ultrasound processor (image courtesy of Hitachi Medical Systems, Steihausen, Switzerland)

Olympus offers two distinct ultrasound platforms. The first one, the Hitachi-Aloka ProSound F75 has imaging frequencies of 5, 6, 7.5, and 10 MHz (Fig. 1.8). Of the many other enhancements, the development of a contrast echo feature (eFlow) enables increased sensitivity to flow at low velocities with microvascularization display to the capillary level, attractive and useful particularly when assessing for the ideal path of access. The other one, the EU-ME2 (and Premier Plus) has frequencies of scanning of up to 12 MHz, providing image quality close to a larger ultrasound processor while maintaining a compact design (Fig. 1.9).

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Fig. 1.8

Hitachi-Aloka ProSound-F75 ultrasound processor (image courtesy of Hitachi Medical Systems, Steihausen, Switzerland)

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Fig. 1.9

EVIS-EUS EU-ME2 Premier Plus ultrasound processor (image courtesy of Olympus Medical Europe, Hamburg, Germany)

Up to recently, there was only one linear echoendoscope option with a unique processor platform. Importantly, the novel Hitachi ARIETTA 850 (Fig. 1.10) is intended to support in the near future both Pentax and Olympus echoendoscopes , with implications regarding costs if both types of scopes are to be used in the same endoscopy unit.

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Fig. 1.10

ARIETTA 850 ultrasound processor (image courtesy of Hitachi Medical Systems, Steihausen, Switzerland)

Accessories

Accessories are devices that assist in the accomplishment of endoscopic procedures. A variety of devices are currently available for therapeutic EUS, depending on the type of procedure.

Transluminal Access

Needles

Transluminal access to perform therapeutic EUS procedures is obtained in the large majority of cases by using standard 19G or 22G fine needle aspiration (FNA) needles, which are available from many manufacturers. The larger 19G needle is preferred to provide access, because it can accommodate a 0.035-inch guidewire that guarantees an improved stability during subsequent interventional maneuvers. However, such a needle is sometimes difficult or impossible to be used when the echoendoscope is extremely bended as in the second/third duodenal portion or for traversing a particularly hard fibrotic pancreatic parenchyma.

Almost all needle designs incorporate proprietary modifications among others to the needle and stylet alloy compositions, needle tip and configuration. For instance, laser etching, mechanical dimpling, or sandblasting of the needle leading tip increase needle echogenicity for better ultrasound visualization. On the other hand, a sharper needle tip allows for a smoother punction, even from oblique angles, while the cobalt-chromium construction brings greater hardness and tensile properties for superior needle penetration as compared to the stainless-steel alloys.

Only one needle specially designed for transluminal access of targeted structures is available on the market , the Echotip Ultra HD ultrasound access needle (Cook Medical, Bloomington, IN, USA) (Fig. 1.11). It possesses a sharply beveled stylet to facilitate needle penetration, housed within a blunt, nonbeveled 19G needle sheath, which has been developed to reduce the incidence of guidewire shearing or fracture during its manipulation.

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Fig. 1.11

The EchoTip® Ultra HD Ultrasound Access Needle , hosting a sharply beveled stylet to facilitate needle penetration, housed within a blunt, nonbeveled 19G needle (permission for use granted by Cook Medical, Bloomington, IN, USA)

Guidewires

Existing single-use straight- or angled-tipped long (>400 cm) guidewires marketed for ERCP use are commonly utilized during therapeutic EUS procedures. As in ERCP, guidewires are essential for maintaining access, for traversing strictures, placing and exchanging of accessories such as those for stricture or fistula dilation and for stent placement. A variety of guidewires are currently available from different manufacturers , and these vary in material, length, diameter, and design to optimize performance. Generally, guidewire passage is easier after flushing the needle with water or saline. Ideal guidewire characteristics for traversing a stricture are generally different from those desired for stent advancement and exchange of accessories. A thinner or more hydrophilic guidewire is preferred for the former, while a stiffer guidewire is more useful for the latter where maintenance of wire position is critical for a safe and effective therapeutic EUS procedure.

As previously mentioned, a 0.035-inch guidewire works only with a 19G needle, and if smaller caliber needles are used, thinner guidewires are needed. For example, a 22G needle accommodates guidewires up to 0.021-inch in caliber. Although there is a small risk of shearing-off of the wire polymer coating jacket when manipulated to-and-fro into a beveled needle [7], coated wires are still generally favored over monofilament stainless steel wires. They offer superior maneuverability due to their hydrophilic tip and effectively insulate against short circuits when used with electrosurgical devices, such as cystotomes or needle knifes. Some authors favor the use of 0.025-inch guidewires with 19G needles, because of the theoretical decreased risk of guidewire shearing than with 0.035-inch wires [8]. Thinner (0.021 or 0.018-inch) guidewires can also be useful for passing tortuous and/or tight strictures, but are poorly visible fluoroscopically, kink very easily and lack stiffness. Therefore, it is difficult to use them for exchanging devices or for stent insertion and for these purposes they are usually exchanged with a larger and stiffer guidewire.

In some difficult cases due to tortuous bile ducts or tight strictures, a sphincterotome, an ERCP catheter (e.g. ERCP catheter, MTW Co., Dusseldorf, Germany) or a steering cannula (e.g. SwingTip Cannula, Olympus Medical Corp.) can be exchanged with the needle over-the-guidewire to facilitate directing and passing-through of the guidewire, while avoiding its shearing-off.

Devices for Tract Dilation

A multitude of existing devices mainly developed for ERCP have been used for fistula tract dilation during various EUS-guided interventional procedures. Following guidewire placement, this can be achieved either with non-cautery devices such as tapered tip ERCP cannulas (e.g. Contour ERCP cannula, Boston Scientific Corporation, Marlborough, MA, USA; Proforma cannula, Conmed Endoscopic Technologies, Utica, NY, USA), biliary dilation bougies (e.g. 5 to 8.5 Fr Soehendra Biliary Dilation Catheter, Cook Medical), or 2 to 4-cm long balloon dilators (generally up to 4 to 8 mm, e.g. REN biliary dilation catheter, Kaneka, Osaka, Japan; Titan biliary dilation Balloon, Cook Medical; Max Pass, Olympus Medical Corp.; or Hurricane Balloon, Boston Scientific Corp.), or with cautery-enhanced devices such as needle-knife sphincterotomes (e.g. Needle knife, Cook Medical) or cystotomes, which can be used in conjunction with regular electrosurgical units (such as VIO300/200, Erbe Elektromedizin GmbH, Tübingen, Germany; or ESG-100, Olympus Medical Systems). All these accessories can be passed over a guidewire through the accessory channel of the endoscope.

The cystotomes deserve a special mention. They are electrocautery devices incorporating a diathermy ring at the distal tip, through which energy is delivered for penetration through the wall of the GI tract and beyond. Most commonly used are the 6- to 10-Fr cystotomes (e.g. Cystotome, Cook Medical; or Cysto Gastro Set; Endo-Flex GmbH, Voerde, Germany) (Fig. 1.12). The 10-Fr cystotome from Cook Medical is also equipped with an additional inner 5-Fr catheter with a separate needle-knife tip, which can be used for direct transluminal puncture avoiding the use of an FNA and for injection of contrast. The diathermic ring of the 10-Fr catheter may be further advanced with cautery to enlarge the newly created fistula tract. The inner lumen of the 10-Fr cystotome can accommodate simultaneously two 0.035-inch guidewires, facilitating the insertion of two drainage devices, such as two stents or a stent and a catheter drain. Because of the large diameter of this device, in Europe smaller 6-Fr to 8.5-Fr cystotomes by Endo-flex GmbH are more frequently used than the larger 10-Fr one that has been almost completely abandoned, especially for bile duct and pancreatic duct drainage where a larger device may be associated with an increased risk of complications. Diathermy catheters, indeed, cause acute and late burn effects around the fistula tract, leading to possible serious side effects including bile leakage, pancreatitis and bleeding [9]. This is the reason why some authors prefer using mechanical tract dilation instead of electrocautery-enhanced accessories and therefore serially exchange multiple devices over-the-guidewire [10].

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Fig. 1.12

(a) The 6-Fr Cysto-Gastro-Set cystotome from Endo-Flex GmbH (Voerde, Germany). (b) The metallic diathermic tip of the device loaded over a 0.035-inch guidewire (adapted with permission from Kawakami H, et al. Gastrointest Endosc 2014;79:338-43) [47]

Drainage

EUS-guided drainage can be performed with naso-biliary, naso-cystic or naso-pancreatic catheter drains, with a variety of biliary either plastic polymer stents or self-expandable metal stents (SEMSs) , or with dedicated self-expandable metal stents, including lumen-apposing and bi-flanged stents.

Catheter Drains

Naso-biliary or naso-cystic catheters are usually used for continuous lavage of the drained duct or cavity in case of walled-off pancreatic necrosis or ongoing infection such as abscesses or ascending cholangitis, and can be easily removed after control of the infection. They can be inserted over-the-guidewire under fluoroscopic guidance. Naso-pancreatic duct catheters are infrequently used, but there are authors who favor their initial placement, followed by replacement with plastic stents in a second intervention [11].

Plastic Stents

For EUS-guided drainage plastic polymer (generally polyethylene) stents of varying sizes, lengths, shapes and different configurations have been used, from 5- to 10-Fr in diameter (mostly related to the diameter of the stented duct/cavity). In theory, they should have pigtails (usually in double pigtail configuration) or flanges, and should be long in order to prevent in- or outward migration. Stents used for EUS-guided pancreatic duct drainage usually have multiple side-holes to facilitate drainage. The stent insertion is performed over-the-guidewire using pushing catheters, with or without an inner guiding catheter, after prior dilation of the fistulous tract, usually to 4 mm.

Placement of more than one side-by-side plastic stents is possible after previous placement of more than one guidewire in parallel. This is usually required in patients with pancreatic fluid collections to decrease the chance of stent blockage and development of secondary infection.

Tubular Self-Expandable Metal Stents (SEMSs)

Standard tubular biliary SEMSs have been used for drainage purposes during EUS-guided procedures. For EUS-guided biliary drainage, they can be used either transluminally or for antegrade stenting [12]. The design of the SEMSs must be covered at least in the transluminal region (e.g. Wallstent, Boston Scientific Corp.; Bonastent, Standard Sci Tech Inc., Seoul, South Korea; Niti-S Biliary, Taewoong Medical Co., Ltd., Gimpo-si, Geyonggi-do, South Korea) [13, 14]. They should be 8 to 10 mm in diameter in order to adequately seal the iatrogenic fistula tract and provide good drainage. Most SEMSs are made of either stainless steel or nitinol, a nickel–titanium alloy resistant to kinking and with a high degree of flexibility. The latter, however, is less radiopaque than stainless steel and additional radiopaque markers have been added in order to ease their deployment in the desired position. Various innovations to the stent design are constantly being developed, such as stents that do not foreshorten during or after deployment (e.g. Viabil, Conmed Endoscopic Technologies) [15], thereby allowing accurate stent placement, or incorporation of fins along the stent body, anchoring flaps or other anti-migration features (e.g. DEUS; Standard Sci Tech Inc.; or Zeostent, Zeon Medical Inc., Tokyo, Japan) [16]. These stents that are not dedicated for therapeutic EUS, when used to create communication between a hollow organ and a cavity, might have an excessive length leading to potential tissue trauma that can cause delayed perforation or bleeding of the contralateral wall.

For EUS-guided hepatico-gastrostomy, long (usually 8 cm or more, with more than 3 cm of stent in the stomach in order to prevent stent maldeployment or internal migration into the peritoneum) [17], tubular fully covered SEMSs have been initially used. The covered design of the intrahepatic portion of the stent can, however, block the intrahepatic biliary ducts, with reported liver abscess formation or focal cholangitis [18]. Moreover, it can impede anchoring of the intra-hepatic portion of the stent. After an initial experience with biliary SEMSs partially uncovered for 1 cm at the distal intrahepatic portion (bare-end type, Niti-S biliary S-type; TaeWoong Medical), a novel generation of stents have been developed and are now available for this indication. The GIOBOR™ stent (Taewoong Medical) was the first stent dedicated for hepatico-gastrostomy (Fig. 1.13) [19]. It is half uncovered in the distal part and half covered in the proximal part, and is available with lengths of 8 to 10 cm and diameters of 8 to 10 mm. Other dedicated stents are now available for this indication, such as the Hanarostent (from MI-tech) that has a short (3 cm) distal uncovered portion, a long covered proximal portion (7 cm) and features an intragastric flap to avoid intraperitoneal migration (Fig. 1.14) [20], or the Bonastent® Biliary Hybrid Stent (Standard Sci-Tech Inc.) available in lengths from 5 to 10 cm and diameters of 8 to 10 mm, featuring anti-migration flaps at the proximal and central part to reduce the chance of stent migration. This stent is delivered via an 8-Fr catheter dedicated device, which makes the release of the stent easy with any angulation of the scope [21].

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Fig. 1.13

The Niti-S™ GIOBOR™ Biliary Stent developed for hepaticogastrostomy under EUS-guidance, half uncovered in the intrahepatic part and half covered in the transluminal and intragastric part. (image courtesy of Taewoong Medical Co., Ltd., Gimpo-si, Geyonggi-do, South Korea)

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Fig. 1.14

(a) The Hepaticogastrostomy Hanarostent, designed by M.I.Tech Co., Ltd., Pyeongtaek-si, Gyeonggi-do, South Korea. It features: (b) a short uncovered distal part; (c) a long covered proximal part; and (d) an intragastric flange to avoid intraperitoneal stent migration equipped with a lasso for easy repositioning and removal (images courtesy of M.I.Tech Co. Ltd.) [20]

In addition, a self-expandable metal stent dedicated for EUS-guided pancreatic duct drainage has been developed [22]. It has a 6-mm diameter and has been successfully used for benign pancreatic strictures in the setting of chronic pancreatitis where it appears to be less traumatic to the pancreatic duct as compared to a larger SEMS.

Insertion of standard tubular biliary SEMSs involves the previously described steps of EUS-guided FNA puncture, guidewire insertion and tract dilation, followed by stent placement and release under fluoroscopic guidance. Perhaps one of the most important developments is the creation of a one-step dedicated stent introducer (Bonastent® Biliary DEUS stent; Standard Sci Tech Inc.), equipped with a 4-Fr tapered metal tip for mechanical dilation of the transmural fistula tract, and with a pre-loaded SEMS on the 7-Fr thin device (Fig. 1.15) [8]. This device greatly simplified the overall procedure without the need of a separate tract dilation maneuver. The included SEMS has an uncovered portion (8 mm in diameter and 15 mm in length) to allow for better anchoring and prevention of occlusion of side branches in the biliary tree, when placed in the liver. Its covered portion (silicone membrane, 6 mm in diameter and 35–85 mm in length) extends transmurally to prevent intraperitoneal bile leakage and ends with a portion featuring anti-migration flaps at the distal part of stent to reduce the chance of intraperitoneal stent migration.

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Fig. 1.15

The Bonastent® Biliary DEUS stent for hepaticogastrostomy (Standard Sci-Tech Inc., Seoul, South Korea). (a) the 4 Fr metallic tip of the 7 Fr stent insertion device; (b) the stent partially deployed; (c) the stent fully deployed (images courtesy of Do Hyun Park MD, PhD) [48]

Lumen-Apposing and Bi-Flanged Self-Expandable Metal Stents

In the last few years, lumen-apposing SEMSs (LA-SEMSs) or bi-flanged SEMSs (BF-SEMSs) have been introduced for a variety of indications (see Table 1.2). All available LA- and BF-SEMSs are made of a braided nitinol mesh with wide flanges and are fully covered by a silicone membrane to prevent tract leakage, as well as, enable easy removability (Figs. 1.16 and 1.17). Their advantages include short length, reduced stent migration and, for LA-SEMSs , ability to provide lumen-to-lumen anchorage by the flanges that are designed to distribute pressure evenly to the luminal wall. Their wide internal diameter (up to 20 mm) offers theoretical advantages in reducing stent occlusion rates, as well as, the possibility for passage of a standard forward-viewing gastroscope for direct intraluminal interventions, such as direct endoscopic necrosectomy, cholecystoscopy and cholangioscopy. Despite many similarities, there are multiple variations between the different LA- or BF-SEMSs including size, shape, delivery mechanisms and availability worldwide.

Table 1.2

Available lumen-apposing and bi-flanged self expandable metal stents for EUS-guided interventions

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Fig. 1.16

AVAILABLE lumen-apposing metal stents: (a) The AXIOS™ stent; (b) The Spaxus™ stent (images courtesy of: (a) Boston Scientific Corp.; (b) Taewoong Medical Co., Ltd.) [49]

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Fig. 1.17

Biflanged self-expanding metal stents developed for EUS-guided procedure: (a) The NAGI™ stent; (b) The Plumber™ Hanarostent; (c) The AIX® stent (images courtesy of: (a) Taewoong Medical Co., Ltd.; (b) M.I.Tech Co., Ltd.: (c) Leufen Medical) [50]

All LA- and BF-SEMSs currently available on the market are intended for pancreatic fluid collections drainage. For this indication, the decision to use one or the other relies on local availability and expertise. The need for a secure drainage and eventual necrosectomy demands the use of a larger stent with a diameter of more than 10 mm. Other indications for the use of these stents include gallbladder drainage, but also bile duct drainage, or gastro-jejunostomy, indications for which only the LA-SEMSs Axios (Boston Scientific Corp.) and Spaxus (Taewoong Medical) have been extensively studied [23].

Lumen-Apposing Metal Stents (LA-SEMSs)

The AXIOS™ Stent and The AXIOS Electrocautery Enhanced Delivery System™

Lumen-apposing metal stents were initially developed for transluminal drainage of pancreatic fluid collections [24]. The first designed LA-SEMS stent was the AXIOS stent, developed by Xlumena Inc. (Mountain View, CA, USA), and purchased by Boston Scientific (Marlborough, MA, USA) in 2015 [23]. The stent has a dumbbell appearance, two large diameter flanges intended for lumen apposition, inner diameters between 6 and 20 mm and a saddle length between flanges of 8 to 10 mm. The handle of the AXIOS delivery system is Luer-locked onto the echoendoscope instrumentation channel inlet port, similar to the standard FNA needle, and is totally controlled by the endoscopist. The handle permits advancement and deployment of the stent in a series of 4 discrete steps under sonographic, fluoroscopic and endoscopic guidance, at the discretion of the operator. The release mechanism provides a hard stop between deployment of the distal and proximal flanges in order to prevent stent maldeployment. Two radiopaque markers on the catheter indicate each end of the preloaded stent for fluoroscopic control, while an endoscopically visible black marker identifies the point at which the proximal stent flange should be released into the gastrointestinal lumen.

Subsequently, the AXIOS stent has been mounted on a cautery device (The AXIOS Electrocautery Enhanced Delivery System™; Boston Scientific Corp.), which includes two thin diathermic wire electrodes positioned 180-degree apart that converge on the conical tip of the device (Fig. 1.18). This allows for direct transmural access without prior FNA puncture and tract dilation using pure cut current [25]. The 9-Fr or 10.8-Fr stent delivery catheters accommodate respectively 6/8 mm and 8/8 mm, or 10/10 mm, 10/15 mm and 10/20 mm stents and make possible to accomplish transluminal access and stent deployment with one single procedure (Video 1.1).

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Fig. 1.18

The two versions available for the delivery system of the AXIOS™ stent: (a) without cautery; (b) cautery-enhanced. (image courtesy of Boston Scientific Corp., Marlborough, MA, USA)

Removal of the AXIOS stent can be done with a snare placed around its waist or by grabbing either its proximal or the distal flange with a foreign-body forceps and exerting gentle traction.

The Spaxus™ Stent

The Niti-S Spaxus stent produced