Large nonpedunculated colorectal polyp management through the lens of an interventional endoscopist

Summary

Minimally invasive endoscopic resection techniques are now the first-line management strategy for most large (> 20 mm) nonpedunculated colorectal polyps (LNPCPs). Appropriate technique selection depends on optical evaluation to predict lesion histopathology alongside the presence of and depth of malignant invasion. We review the indications and performance of endoscopic mucosal resection, cold snare resection, and endoscopic submucosal dissection. These complementary techniques, bolstered by site-specific technical modifications and ancillary techniques, are an effective, efficient, and safe alternative to surgery. An understanding of the role of minimally invasive endoscopic resection techniques is crucial for all endoscopists and surgeons involved in LNPCP management.

Large (> 20 mm) nonpedunculated colorectal polyps (LNPCPs) are commonly encountered by all endoscopists; LNPCPs occur in about 8% of screening colonoscopies following a positive fecal immunohistochemistry test.¹ Minimally invasive endoscopic resection techniques are now the first-line management strategy for the vast majority of LNPCPs because of their efficacy, safety, and cost-effectiveness compared to surgery.² As surgeons serve a critical role in colorectal cancer screening and LNPCP management, familiarity with the gamut of endoscopic resection techniques and their indications can optimize patient outcomes. We provide a practical overview of the pre-resection, resection, and postresection phases of LNPCP management.

Optical evaluation

Optical evaluation refers to interrogation of LNPCP size, location, morphology, and surface pit and/or microvascular pattern to predict lesion histopathology, submucosal invasive cancer (SMIC), and SMIC depth of invasion. This is achieved by image-enhanced endoscopy (e.g., narrow band imaging [NBI], dye chromoendoscopy) and established optical evaluation classifications (NBI International Colorectal Endoscopic [NICE], Japan NBI Expert Team [JNET]).^3,4 Therefore, optical evaluation has become the crucial step in LNPCP management, as it informs therapeutic decisions.

Optical features can differentiate serrated and adenomatous lesions. Using image-enhanced endoscopy, serrated lesions are characterized by regular dark or white spots, may have isolated lacy vessels, and appear similar to surrounding mucosa (NICE I, JNET I). In contrast, adenomatous lesions have vessels in a regular distribution and appear more brown than the surrounding mucosa (NICE II, JNET IIA).

Although numerous optical evaluation classifications exist to predict SMIC, a unifying theme is the identification of a demarcated area with loss of surface pit and/or microvascular pattern homogeneity. This commonly coincides with depressed morphology (Paris 0–IIc). Optical features can further stratify SMIC depth with irregular distributions of the microvasculature with variable caliber (NICE II, JNET IIB), suggesting high-grade dysplasia/superficial SMIC (< 1000 μm depth of invasion), whereas amorphous areas, disrupted microvascular patterns, or distorted surface pits (NICE III, JNET III) represent deep SMIC (≥ 1000 μm depth of invasion).⁴ In the absence of these features, location, morphology, and granularity can be used to define a group of LNPCP with an increased risk of invisible or covert SMIC (> 10% risk; rectosigmoid 0–IIA+IS granular, 0–IS/0–IIA+IS nongranular).⁵

Endoscopic resection techniques

Endoscopic mucosal resection

Endoscopic mucosal resection (EMR) is a well-described inject and resect technique. First, colloid injectate is introduced into the submucosa to lift the lesion. The snare is then placed over the polypoid area with inclusion of a 2-to 3-mm margin of normal mucosa and closed to transect tissue using a microprocessor-controlled electrocautery unit. After each resection, the defect is irrigated to identify any residual polypoid tissue and assess for deep mural injury. The edge of the previous defect marks the beginning of the next resection. These steps are then repeated sequentially until all polypoid tissue is removed with a healthy margin of normal mucosa.⁶

Cold snare resection

In place of electrocautery, mechanical transection is achieved by using a dedicated stiff thin-wire snare. Submucosal injectate is not required but, anecdotally, improves lesion demarcation, and the addition of dilute epinephrine (1:100 000) can reduce intraprocedural bleeding. Like EMR, cold snare resection (CSR) is performed systematically with a snare until all polypoid tissue is removed with inclusion of a normal mucosal margin. As no electrocautery is used and resection is more superficial, CSR mitigates the risk of clinically important bleeding after endoscopic resection and deep mural injury.⁷ Cold snare protrusions can form from compression of submucosa and muscularis mucosa during transection but have not been associated with recurrence.⁸

Endoscopic submucosal dissection

Endoscopic submucosal dissection (ESD) is an organ-preserving en bloc resection modality that uses a distal cap and endoscopic electrosurgical knife to dissect underneath the LNPCP in the submucosal plane. However, in general, ESD is more time consuming and has a greater risk of adverse events than EMR.^9,10 Thus, advanced training in addition to traditional interventional endoscopy fellowships is required to perform ESD.

Selective resection algorithm

Current endoscopic resection techniques are complementary, depending on their efficiency, safety, and ability to achieve R0 resection for low-risk SMIC. For most LNPCPs without concern for SMIC, including complex LNPCPs involving the ileocecal valve, appendiceal orifice, and anorectal junction as well as previously attempted and circumferential LNPCPs, EMR is the primary modality owing to its efficacy, efficiency, and safety compared to surgery and ESD.^11–15 Sessile serrated lesions without dysplasia are amenable to CSR, with similar technical success and recurrence as EMR but less risk of deep mural injury and clinically important bleeding after endoscopic resection.⁷ Lesions with features of superficial SMIC or high risk for covert SMIC require en bloc resection with ESD, transanal endoscopic microsurgery, or transanal minimally invasive surgery, depending on lesion location and available expertise. If optical features of deep SMIC are identified, these lesions should be referred for surgery or multidisciplinary review (Figure 1).

Fig. 1.

Selective resection algorithm. (A, B) NICE I, JNET I lesion. (C, D) NICE II, JNET IIA lesion. (E, F) JNET IIB, or distal 0–IIa+Is granular lesion in rectosigmoid, representing covert SMIC. (G, H) NICE III, JNET III lesion. *En bloc resection can be achieved with endoscopic submucosal dissection, transanal endoscopic microsurgery, or transanal minimally invasive surgery, depending on lesion location and local expertise in interventional endoscopy and surgery. G = granular; JNET = Japan NBI Expert Team; NBI = narrow-band imaging; NICE = NBI International Colorectal Endoscopic; NG = nongranular; SMIC = submucosal invasive cancer.

Adverse outcomes

Clinically important bleeding after endoscopic resection

Although clinically important bleeding occurs in about 6% of patients, conservative management is appropriate in most cases. Cold snare resection for large sessile serrated lesions and defect closure after EMR with through-the-scope mechanical clips for proximal LNPCP are effective mitigating strategies.¹⁶

Deep mural injury

The most concerning adverse event is substantial deep mural injury, denoted by Sydney classification type III (muscularis propria injury), IV, or V (transmural injury with or without contamination, respectively). Substantial deep mural injury occurs in about 3% of patients who undergo EMR and is associated with attempted en-bloc resection, advanced histopathology, and transverse colon location.¹⁷ Use of a 15-mm stiff snare across haustral folds and in the right colon may reduce the risk for substantial deep mural injury, whereas a 20-mm snare can be used in the left colon and rectum. Prolonged transection requiring more than a few pulses of a microprocessor-controlled electrocautery unit can suggest inadvertent entrapment of muscularis propria. Following each resection, irrigation of the defect with dye chromoendoscopy should highlight nonstaining muscularis propria. This may represent possible substantial deep mural injury, which should be closed using through-the-scope mechanical clips to prevent further sequelae.

Recurrence

The LNPCP recurrence rate has historically been about 15%, mostly occurring within 6 months. Recurrence can be successfully treated endoscopically, leading to a long-term adenoma-free rate of 98.1%, underscoring the importance of close surveillance following EMR.^18,19 At the time of the resection, the risk of recurrence can be mitigated with meticulous margin visualization and ensuring resection of a 2- to 3-mm rim of normal mucosa to prevent residual polypoid tissue, which can be obscured by diathermy on defect evaluation. Further, post-EMR thermal ablation to the margins of the defect with snare tip soft coagulation or hybrid argon plasma coagulation further reduces recurrence rates to pooled rates of 4% and 9%, respectively.²⁰ Endoscopic submucosal dissection has a 0.5% recurrence rate and is generally amenable to further endoscopic treatment.²¹ Thus, initial surveillance colonoscopy should occur at about 6 months to evaluate the postresection scar and assess for any metachronous lesions.

Referral to an interventional endoscopist

All LNPCPs without optical features of deep SMIC are appropriate for referral to a specialist with a focus in minimally invasive endoscopic resection techniques or a polyp adjudication committee, depending on availability. Complex lesions that should be considered for referral include those with prior attempts at endoscopic resection; nonlifting lesions; lesions involving the anorectal junction, appendiceal orifice, ileocecal valve, or a diverticular opening; and lesions with optical features concerning for superficial SMIC.

Conclusion

Endoscopic resection has a synergistic role with surgery in the management of early colorectal neoplasia. Owing to their efficacy, safety, and cost-effectiveness, EMR, CSR, and en bloc resection techniques should be considered the primary management strategy for most LNPCPs. Therefore, it is imperative for all endoscopists to appreciate the expanding role of these techniques alongside optical evaluation as a tool for optimal technique selection.