The goal of submucosal injection is to elevate and bring forward the lesion into the lumen to provide good visualization of the margins and allow assessment for resection. Before injection, the assistant should prime the needle with saline solution to prevent injection of air into the bowel wall causing iatrogenic pneumatosis . Injection should begin at the proximal aspect of the lesion, the side farthest from the scope, and proceed distally. If it is started at the distal aspect of the lesion, the lesion may fall away from the scope, reducing visualization and making resection difficult. Whenever possible, the injector needle should be placed tangential to the mucosal surface; this facilitates insertion of the needle into the submucosal plane and decreases the risk of intraperitoneal injection. Puncture is made immediately adjacent to the lesion [4, 8]. Injecting directly through the lesion has raised some concerns regarding the risk of needle tracking of neoplastic cells into deeper layer of the wall [9].

Injection begins when the needle touches the mucosa and is continued as the needle is advanced towards the submucosa. There is immediate elevation of the lesion upon entering the submucosal space. This confirms injection into the correct plane. Lack of elevation or intraluminal extravasation of injection solution may mean lack of injection into the correct plane. In this instance, the needle can be advanced or withdrawn until the correct submucosal plane is identified. When resecting large lesions in a piecemeal fashion, segmental injection and resection is recommended, especially when using normal saline (NS) as the injection solution. The volume of injection solution used during the entire procedure varies and depends on the size of the lesion and type of solution used.

If there is lack of elevation despite appropriate injection technique, this ‘nonlifting sign’ (Fig. 15.1) may indicate fixation of the lesion to the underlying submucosal tissue. This can be due to fibrosis from previous resection attempts, underlying colitis, or malignant infiltration into the deeper tissues. Occasionally, even benign lesions without underlying colitis or fibrosis may fail to elevate. Intervention in these cases is often limited to a biopsy, and presence of more invasive disease on the biopsy necessitates surgical resection [4, 8].

Following submucosal injection, resection is performed using an endoscopic snare . A variety of snares are available ranging in size, stiffness, configuration, and shape. The snare is placed on top of the lesion, opened, and placed around the base of the lesion with the scope angled downwards. The assistant then begins to close the snare while advancing the catheter, to maintain the position of the snare at the base of the lesion. Once the snare is closed at the base, transection of the lesion is performed using electrocautery. Large size snares are often employed as they allow en bloc resection of the target lesion and piecemeal resection of large lesions in as few pieces as possible. The supplementary Video 15.1 provided with this chapter shows endoscopic resection of a mucosal resection using I-EMR.

All attempts should be made to perform an en bloc resection . This allows for evaluation of resection margins for completeness of resection, provides for more accurate histopathological assessment, and also reduces the risk of recurrence when compared to piecemeal resections. If en bloc resection is not possible piecemeal resection is performed starting at one margin of the lesion and proceeding until the entire lesion is resected. Care must be taken to include the margin of previous resection, so that residual tissue bridges are not left behind. Once piecemeal resection is complete, the lesion site should be inspected for presence of residual tissue. If present, the residual tissue should be resected using an appropriate sized snare [4]. Figure 15.2 depicts piecemeal resection of a lesion greater than 20 mm.

Following complete resection of the lesion, some endoscopists choose to ablate the resection margin and any residual tissue to decrease the risk of local recurrence. Options include argon plasma coagulation (APC), thermal ablation with the tip of the snare (snare tip soft coagulation), and hot biopsy forceps (hot avulsion technique) [8, 10].

First described by Inoue in 1990 [11] and most commonly used for resection of mucosal lesions in the esophagus, this technique can also be employed in the colon and rectum. Like I-EMR, it also uses submucosal injection to lift the target lesion following which resection is performed using dedicated mucosectomy devices. These are single-use devices that have a cap fixed to the tip of the scope and are equipped with a specially designed electrocautery snares. Caps are available in various sizes and have either a flat, cylindrical, or oblique end.

To begin resection the snare is opened and positioned on the internal rim at the tip of the cap. The scope with the attached cap is then positioned on top of the target lesion. Suction is applied to capture the lesion into the cap and the snare is deployed at the base of the lesion. Finally, electrocautery is applied to resect the target lesion [8]. Figure 15.3 shows resection of a mucosal lesion using this technique.

One must be careful when applying suction to capture the lesion as it may involute the full thickness of the wall resulting in capture of the muscularis propria in the snare. It also tends to collapse the lumen which compromises the endoscopist’s view. Concern over the risk of full thickness resection has limited its application in the colon.

Originally extrapolated from variceal band ligation , this technique is somewhat similar to C-EMR. Specially designed band ligation devices with caps are used to create a neo-polyp. These devices are attached to the tip of the endoscope and positioned on top of the target lesion. Suction is applied to retract the lesion in the cap following which the band is deployed at the base of the lesion. Standard snare electrocautery is then used to resect the neo-polyp above or below the band [8]. Figure 15.4 shows resection of mucosal lesion without the use of submucosal injection.

Binmoeller et al. in 2012 described a novel technique of performing resection by immersing the lesion under water. This was based on their observation of the colonic wall when viewed with an endoscopic ultrasound (EUS) . They noted that when filled with water, the muscularis propria remained circular and mucosa and the submucosa remained involuted. Furthermore, the buoyancy effect of the disease-affected mucosa allowed the mucosa and the submucosa to “float” away from the deeper muscularis propria eliminating the need for submucosal injection and the costs associated with injection needles and specialized injection agents.

Water immersion enhances the sensitivity of endoscopy by creating an optical “zoom” effect that magnifies the mucosa. Narrow band imaging can be used to further enhance the contrast between the diseased and normal mucosa. On the other hand, lack of air insufflation prevents overdistention and subsequent thinning of the wall thus decreasing the risk of perforation.

A routine adult-sized single-channel colonoscope with an auxillary water jet is used for this technique. Upon reaching the target lesion luminal air is suctioned and sterile water is instilled to fill the lumen. Between 500 and 1000 mL of sterile water at room temperature is needed to achieve complete filling of the lumen. Continuous water infusion can be used to limit contractility which can compromise visibility. Margins of resection are marked using the APC probe tip prior to resection.

Duckbill snare is used to perform resection. Starting at the margin of resection the snare is opened, pushed against the bowel wall, and torqued to capture a piece of the tissue. The snare is then closed and electrocautery is applied to transect the tissue. Large lesions may require piecemeal resection taking care not to leave behind any residual tissue. Remnant tissue too small to ensnare can be coagulated with hot biopsy and forceps and APC can be used to ablate the resection margins [8, 9, 12].