Louis M. Wong Kee Song, MD
Endoscopic mucosal resection (EMR) refers to injection-assisted, cap-assisted, or band-assisted resection of superficial lesions confined to the mucosal and submucosal layers of the gastrointestinal (GI) tract. Injection-assisted EMR is commonly performed in the colon to facilitate lesion resection and reduce the risk of perforation associated with the removal of large polyps. Dedicated cap- and band-assisted EMR devices are commonly used in the esophagus and to a lesser extent in the stomach, but have limited applicability in the duodenum and colon owing to a high risk of perforation. A working knowledge of the devices and accessories available for EMR is essential for the safe and successful performance of the procedure.
Devices and Accessories
Injection-Assisted Endoscopic Mucosal Resection
Simple polypectomy refers to cold or hot snaring of lesions without prior submucosal fluid injection, whereas injection-assisted EMR implies injection of a solution in the submucosal space underneath the lesion to provide a safety cushion between the mucosal and deeper layers of the GI wall prior to snare resection. Based in part on size, the lesion can be resected en bloc (< 2 cm) or in a piecemeal fashion (≥ 2 cm).1
The principles of electrosurgery and recommended electrosurgical settings for EMR are discussed in a separate chapter. Familiarity with the use of a particular electrosurgical generator and designated settings for selected devices (eg, hot snare or hot biopsy forceps) is essential to enhance safety and performance of EMR.2,3
In some instances, peripheral marking of the lesion is desired. This is particularly helpful when encountering a flat lesion because its border may efface or become indistinct during submucosal fluid-lifting of the lesion. Several accessories can be used for the purpose of placing coagulation dots around the periphery of the lesion, including argon plasma coagulation (APC), an electrosurgical knife (eg, DualKnife, Olympus), or the tip of a snare set on coagulation mode.
Various injection catheters are available for the purpose of submucosal fluid injection (Figure 10-1). They range from 5 to 10 Fr in sheath diameter and 160 to 350 cm in length, and incorporate 19- to 25-gauge needles that extend 4 to 8 mm at the tip.4 The iSnare (US Endoscopy, Inc) integrates a 2.5 × 4 cm snare in a 10 Fr injection catheter. Although a 25-gauge injection needle is adequate for saline-assisted EMR, a 23-gauge or larger injection needle is preferable when viscous solutions are utilized.
Various solutions can be injected in the submucosal space with intent to obtain a safety cushion, enhance access, and/or facilitate grasping of lesions. These injection solutions are discussed in detail in a separate chapter.
The most readily available and widely used solution is normal saline (NS), but the saline-assisted lift generally dissipates within 2 to 3 minutes. A longer-lasting fluid cushion can be achieved with the use of a viscous solution, such as hyaluronic acid, succinylated gelatin, and hydroxypropyl methylcellulose.5 In a randomized, double-blind trial, the use of such a viscous solution (succinylated gelatin) reduced procedural time and number of resections per lesion during piecemeal EMR relative to NS.6
Most of these injection solutions are used off-label. In the United States, one agent (Eleview, Aries Pharmaceuticals) was approved recently by the US Food and Drug Administration for submucosal injection. Eleview is commercially available as ready-to-use, premixed ampoules that contain a low-viscosity emulsion consisting of medium-chain triglycerides, polymers, water, and NS, as well as methylene blue. An effective lift averages 15 minutes but the fluid cushion can last up to 45 minutes. In Japan, a 0.4% solution of hyaluronic acid is approved for commercial use as a submucosal solution (MucoUp, Johnson and Johnson).
A few drops of methylene blue or indigo carmine are commonly added to the injection solution because the dye enhances delineation of the lesion/normal mucosa interface. The dye also aids in recognition of the target sign postresection, indicative of muscularis propria injury (Figure 10-2). Oversaturation of the solution by the staining agent should be avoided because of light absorption by the dye and darkening of the field of view (Figure 10-3).
Dilute epinephrine can be added to the injection solution to lessen the occurrence of immediate bleeding and facilitate visualization during EMR by keeping the resection field dry. It does not prevent delayed bleeding, however. At dilutions commonly used for EMR (1:100,000 to 1:200,000), the submucosal injection of epinephrine is generally safe and systemic effects, such as hypertension and tachycardia, are mitigated.
Numerous disposable snares of various shapes, diameters, wire composition (monofilament or braided), and rotation capability are available.7 Reusable snares are also available, but rarely used because of infection-control issues. The snares can be round, oval, hexagonal, crescent, and duck bill in shape, to name a few (Figure 10-4). The selection of a particular snare(s) depends on the size, location, and characteristics of the lesion, as well as operator preference. For instance, a stiff snare (eg, SnareMaster Spiral, Olympus) is preferable for a flat polyp to minimize bending and slippage of the snare over the lesion (Figure 10-5). A duckbill-shaped snare (eg, AcuSnare, Cook Medical) can be most useful for removal of a polypoid lesion behind or along a fold. Stiff minisnares (eg, Exacto Cold Snare, US Endoscopy, Inc) are particularly suitable for cold snaring of diminutive residual polyp tissue at the edge or within the mucosectomy defect. Operator experience in selecting and handling snares is necessary for their optimal use.
Adjunctive Ablative Devices
Residual polyp tissue that cannot be removed by snare methods may be destroyed by ablative modalities, such as APC and hot biopsy forceps avulsion. Compared with APC, however, hot biopsy avulsion of visible residual adenoma at the time of EMR significantly decreased the recurrence rate (odds ratio 0.079; P < .001) without significantly increasing the risk of the procedure.8 The avulsion technique involves grasping and tenting the tissue, followed by cutting current application (eg, ENDO CUT I, Erbe) and traction removal of the tissue.