Douglas K. Rex, MD
Endoscopic mucosal resection (EMR) in the gastrointestinal tract refers to submucosal injection following by snare resection. For lesions < 2 cm in size, EMR can often be performed en bloc. Most lesions that are ≥ 20 mm are resected piecemeal. This chapter describes large-area piecemeal EMR in the colorectum. Most broad lesions are granular, because granular lesions tend to grow laterally for long periods before developing invasive cancer. Granular lesions have less submucosal fibrosis than nongranular lesions. The combination of low risk of cancer and minimal submucosal fibrosis makes large-area granular laterally spreading tumors (LSTs) excellent targets for EMR.
Saline is used commonly as a submucosal injection fluid, and is safe and inexpensive. However, many experts have abandoned saline for widefield EMR because more viscous injection solutions, including succinylated gelatin1 and Eleview,2 have been shown in randomized controlled trials to produce more concentrated submucosal injection mounds that persist longer and allow resection in fewer pieces. Hydroxyethyl starch (hetastarch) is widely available in the United States and has properties similar to succinylated gelatin. Viscous solutions are more easily injected through a 23-gauge needle.
The injection fluid should include a contrast agent, typically either indigo carmine or methylene blue. Indigo carmine is available commercially as a 0.8 mL solution in 5 mL vials. One vial in a 500 mL bag of injection fluid provides a deep, rich blue color with excellent submucosal staining properties. We prepare one bag each morning, keep it in a clean area, and draw 10 mL aliquots from the bag throughout the day as needed. Endoscopists should check whether this practice is compatible with local pharmacy rules. For methylene blue, one 10 mL vial of 1% solution is used per 500 mL of injection fluid. The contrast agent in the submucosa delineates the border of the lesion during injection, which is of particular value for serrated lesions (Figure 14-1). The contrast agent also stains the submucosa blue (Figure 14-2), which facilitates recognition of muscle injury.3 Cut muscle appears typically as thick, white parallel bands in the resection defect, and as a circle of white on the cut surface of the specimen (Figure 14-3). Since thermal injury is also white in color (if either no fluid is injected or if excessive coagulation current is applied), the keys to identifying cut muscle are to stain the submucosa with contrast and limit thermal injury.
|INJECTION STRATEGY||LESION TYPE|
|Central injection||Appropriate for most 2- to 4-cm lateral spreading lesions for which much of the lesion is visible in the forward view|
|Proximal edge injection||Appropriate for many lesions for which a substantial portion of the lesion is on the proximal side of a haustral fold|
|Distal to proximal injection||Appropriate for very broad (> 4 to 6 cm) lesions|
The overriding principal of injection strategy for EMR is that the injection should facilitate resection. Injection can and frequently should proceed directly through the lesion, though injection directly through an area of ulceration or Narrow Band Imaging (Olympus) International Classification Endoscopic III features (potential cancer) is contraindicated. Endoscopic resection is also contraindicated when such features are present.4
Injection strategies can be roughly separated into 3 types (Table 14-1). Most commonly used is central injection, which is particularly appropriate for lesions of 2 to 4 cm (Figure 14-4). Injection proceeds into the center of the lesion, with an effort to finish injection with the lesion on top of a focused, dome-shaped submucosal injection mound. Proximal edge injection may be the best approach to 2 to 4 cm lesions that are draped over a haustral fold, so that much or most of the lesion is not visible with the colonoscope tip in its standard forward-looking position. For proximal edge injection, the ideal position for the initial injection is at the precise junction of the proximal limit of the lesion and normal mucosa. In some cases this initial injection is best made with the instrument in retroflexion5 (Figure 14-5). Retroflexion is safe using adult or pediatric colonoscopes in the cecum, ascending, transverse colon, and rectum, but in the descending and sigmoid may be more safely accomplished using an upper endoscope. For very broad lesions, which are usually granular, the best injection approach is to begin at the anatomic distal end of the lesion, inject under the distal aspect, resect the distal aspect, and then move proximally using a process of repeated injection, resection, and reinjection, until the most proximal aspects of the lesion have been resected. Anticipating how the injection/resection process will proceed is an important skill gained by experience.