Colonoscopic Polypectomy, Mucosal Resection, and Submucosal Dissection

Indications and Contraindications

Treatment decisions must consider whether substantial risks exist and whether the patient's overall life expectancy is likely to be affected by the generally slow progression of colonic adenomas. The average transition time from non-advanced adenoma to cancer has been estimated to take more than 20 years, so patients with advanced comorbid illnesses and limited life expectancy may not benefit from adenoma resection.

Colonoscopy is usually inappropriate in patients who are pregnant or have fulminant colitis, suspected intestinal perforation, fresh intestinal anastomosis, a recent myocardial infarction, or stroke. With respect to antithrombotic management, polypectomy and mucosal resection are considered higher risk procedures and should generally not be performed in patients who have uncorrected bleeding disorders. High-quality bowel preparation is crucial for detection of subtle lesions and for resection of particularly large or difficult lesions when an elevated risk of perforation exists. Poor bowel preparation is also a contraindication for performance of complex polypectomy due to the risk of peritoneal contamination in the event of a perforation.

Management of Antithrombotic Agents

Polypectomy and mucosal resection are considered procedures at higher risk for bleeding. Risks related to interrupting antithrombotic medications for polypectomy need to be balanced against the risks of significant bleeding during and after the procedure. Recommendations for the management of antithrombotic agents are provided in the recently updated American Society for Gastrointestinal Endoscopy (ASGE) guidelines.

Antibiotic Prophylaxis for Endocarditis

The ASGE and the American Heart Association guidelines state that antibiotic prophylaxis solely to prevent infective endocarditis is no longer recommended before endoscopic procedures, including diagnostic colonoscopy and polypectomy.

Colonoscope

The choice of colonoscope is dependent on personal preference. It needs to promote adequate position, visualization, and resection of the colonic lesion. The colonoscope should allow adequate flushing and be equipped with a water jet. Simethicone is often added to water to eliminate gas bubbles and improve visualization. Simethicone residue within the endoscope may be difficult to remove, and some manufacturers recommend the lowest dose of simethicone possible.

CO ₂ Insufflation

Insufflation should be done with CO ₂ . Its clinical utility as an insufflating gas for colonoscopy has been well established. CO ₂ is readily absorbed through the colonic mucosa. Because of the lower amount of retained gas in the colon, patients are more comfortable and less likely to have abdominal pain following the procedure. It is also nonflammable, and the risk of colonic perforation, which has been reported with air insufflation, should be zero. Finally, there have been rare case reports of fatal air embolism with other endoscopic interventions. Such risk does not exist when using CO ₂ as the insufflating gas.

Snares

Both the endoscopist and the endoscopy assistant must be familiar with the type of snare used. These individuals must understand and have tactile knowledge of the opening and closing of the snare, the closing pressure required to produce optimal coagulation, and the relationship between the size of the tissue being strangulated and the amount of snare being closed. Various snares, each with a slightly different feature, are used for polypectomy and mucosal resection. The choice is based on personal preference, the size of the lesion, and the applied technique. Typically, small snares are used for small polyps, and larger snares for larger polyps. Stiffer snares are used for colonoscopic mucosal resection so that flat or depressed lesions and a healthy margin can be more easily captured in the snare.

Injection Fluid

EMR and ESD generally require submucosal injection. Saline injection tends to be adequate for most cases of EMR. For more complex EMR cases and for all colorectal ESD, a solution that provides a longer-lasting submucosal cushion is highly recommended. At present in the United States, there is only one Food and Drug Administration–approved submucosal injectate (Eleview, Aries Pharmaceuticals, Inc., San Diego, CA). It contains a composition of polymer chains to provide a lasting cushion and methylene blue. Clinical studies are lacking, but preliminary data from animal model work appear promising. Based on local availability the following solutions can be used off label:

• Normal saline can be used in the majority of cases of colonic EMR.

• Worldwide, hyaluronic acid (MucoUp, Seikagaku Corporation, Tokyo, Japan) is the most commonly used injection solution for colorectal ESD.

• Sodium hyaluronate (Healon, Abbott, Chicago, IL) dispensed as 10 mg/mL. 0.85-mL syringe is available in the US and is approved for intraocular injection during ophthalmic surgery. A typical dilution for ESD is one 0.85 mL syringe of hyaluronic acid mixed with 2.5 mL of normal saline and dye (indigo carmine or methylene blue) to desired color. Although this type of solution provides for excellent submucosal lift, the cost tends to be prohibitive for routine use.

• Hydroxyethyl starch (Hetastarch; available as Voluven, Fresenius Kabi Ltd., Runcorn, United Kingdom or Hespan, B. Braun Medical, Melsungen, Germany) dispensed as 500-mL bags. No dilution is necessary, dye can be added to the desired color, and the solution can be directly used for submucosal injection at the time of ESD. No data are available for the use in ESD, but a randomized controlled study showed that hydroxyethyl starch is superior to normal saline for EMR.

• Hypromellose (Gonak, Akorn, Inc., Lake Forest, IL) is an ophthalmic solution used as artificial tears and is dispensed as a 15-mL vial. Typical dilution for ESD is to mix one 15-ml vial with 85 mL of normal saline. The use of hypromellose has been shown to be safe and effective in EMR, but data specifically pertaining to ESD are not available.

• Succinylated gelatin (Gelufusine, B. Braun Medical) is a volume expander that is not available in the US. Its physical properties are similar to hydroxyethyl starch. It has been shown to reduce the number of resections during piecemeal mucosal resection and overall procedure time when compared with normal saline solution.

Electrocautery

High-frequency electrical current is employed to facilitate cutting and to coagulate vessels at the resection margin. Electrical current is transformed to heat at high frequencies. The amount of heat that is produced in the tissue and determines cautery effects is dependent on the current density and tissue resistance. Current density is dependent on the contact (e.g., snare diameter); the smaller the contact area the higher the current density and the higher the heat. During polyp resection, the snare serves as the active electrode (high current density and heat), and the circuit is completed via a conducting grounding pad that is affixed to the patient's skin. Whereas current density is high at the snare, it is low at the grounding pad, and typically not noticed by the patient.

Most electrocautery units allow three cautery modes: cutting , coagulation , or a blend of both. The cutting mode delivers a continuous sine-wave voltage pattern. When sufficient voltage is delivered with a resultant high current density, electrosurgical cutting ensues. This mode allows a swift cut through tissue without deep thermal tissue injury. The polyp base is desiccated based on the applied mechanical pressure of the snare loop onto the polyp base. This mode does not provide sufficient cautery time to seal blood vessels and bleeding is therefore a concern. In contrast, the coagulation mode provides less high-density current and therefore less heat. The tissue is coagulated while the snare is closed. This type of electrocautery snare resection may be considered a mechanical cut supported by coagulation. The concern is deep mural cautery injury. To minimize risk, cautery units provide a setting of cutting current alternating with coagulation current, also called blended mode. Realizing that heat production is dependent on tissue resistance, which is dependent on water content and changes during cautery, some cautery units provide a microprocessor-controlled current, which adjust the delivered energy to tissue resistance. This approach may optimize coagulation and cutting effects, and minimize risk.

Data on the optimal electrocautery mode are limited. A 2004 survey found that 46% of US endoscopists used blended and 46% coagulation mode. Two retrospective studies suggest that coagulation may increase the risk of delayed bleeding and blended current of immediate bleeding. Thus, the optimal electrocautery mode for polyp resection remains an important clinical question.

Argon Plasma Coagulation

Argon plasma coagulation (APC) is often used during EMR to cauterize residual polyp tissue and to ablate the resection margin. APC produces electrically conducting argon plasma by guiding argon gas through a delivery catheter that also contains an electrode for delivery of high-frequency current. APC generally creates uniformly deep zones of desiccation, coagulation, and devitalization less than 3 mm in depth. Because the argon plasma conducts the current, APC can be applied without tissue contact.

Other Instruments

Other instruments that are often used during polypectomy and mucosal resection include the standard sclerotherapy injection needle, endoclip, endoloop, and retrieval net. Detailed examples of use of these instruments, which are important for colonoscopic resection, are described subsequently in the section on Techniques.

Assessment of the Polyp

The macroscopic classification of adenomas and early colorectal neoplasms is crucial in the discussion of diagnosis and treatment of early CRC. Typically, endoscopic resection can be considered for mucosal lesions. Submucosal lesions may require additional endosonographic evaluation. The following characteristics affect the decision whether to resect and what approach to choose.

Size

Several studies have shown variability in estimation of polyp size. To minimize subjectivity, a reference tool may be used to estimate size. For instance, snares have predefined opening diameters and can serve as a reference (e.g., 10 mm) when positioned on or aside the polyp ( Fig. 37.1 ). Furthermore, the snare catheter has a determined size (2.4 mm) and can also serve as a reference tool. Catheter tips could also be marked (mm/cm) to allow a more accurate assessment of size; however, this is cumbersome in clinical practice, and more applicable to studies. Because risk and surveillance management is based on size ranges, one may label polyps of 10 mm or less as diminutive (1–5 mm) and small (6–9 mm), estimate large (≥ 10 mm) by 5-mm increments up to 30 mm, and 10-mm increments for larger lesions. For very large lesions, the extent of the lesion circumference (25% increments) and across more than one fold should be noted, as these may affect difficulty of resection or risk of stenosis. To recognize the full extent of a lesion also requires clear visualization of the margin of the lesion. Digital or traditional chromoendoscopy typically help to contrast the lesion from the normal mucosa. A distal attachment cap is helpful to “spread out” the lesion slowly and inspect the margin. Submucosal injection with a contrast agent may further demarcate the lesion more clearly. Marking of the margin may be helpful in some cases before mucosal resection and submucosal dissections.