May 19, 2017
What makes a polypectomy complex or difficult?
Colonoscopy has become an accepted screening and surveillance modality for colorectal cancer, and endoscopic polypectomy has been widely adopted as an effective therapeutic tool. Most gastroenterologists can endoscopically excise the majority of polyps found on a routine colonoscopy. Polyp size, location and morphology, however, are characteristics that can make endoscopic excision more challenging. Sessile or pedunculated polyps greater than 2 centimeters in diameter, as well as flat or depressed polyps, fall into this category.
Additional characteristics that can also make polyp excision difficult include:
- Location within a colonic flexure or behind a fold that is difficult to access
- Location within an area of severe diverticulosis, involving the ileocecal valve or appendiceal orifice, or in intimate contact with the dentate line
- Polyp wrapped around a fold in a clamshell fashion
- Polyp occupying more than one-third of the colonic circumference
- Polyp crossing over two haustral folds
- Scarred residual polyp from prior attempts at resection
Is the polyp benign or malignant?
Visual inspection during colonoscopy can help establish whether a polyp is benign or malignant. Ominous signs that the polyp likely contains invasive malignancy include ulceration, induration, a depressed center and friability. However, up to 10 to 15 percent of large polyps without these characteristics harbor invasive carcinoma. Enhanced imaging using electronic (for example, narrow band imaging) or dye-assisted (for example, indigo carmine) chromoscopy is useful in identifying vascular and mucosal pit patterns that are suggestive of deeper malignant invasion precluding endoscopic resection.
Which polyps are amenable to endoscopic mucosal resection?
Endoscopic mucosal resection
Endoscopic mucosal resection. A. Large flat polyp in proximal ascending colon. B. Lifting of lesion following submucosal fluid injection. C. Piecemeal resection. D. Post EMR defect.
Colonic endoscopic mucosal resection (EMR) consists of submucosal fluid injection to lift the polyp from the muscularis propria followed by snare resection of the lesion en bloc (in one piece) or in a piecemeal fashion. Although dedicated mucosectomy devices, such as cap- or band-assisted EMR, are commonly utilized in the esophagus and stomach, they are avoided in the thin-walled colon due to the high risk of perforation. When compared with surgical excision, EMR offers preservation of the colon, and decreased morbidity and cost. Removal via EMR is generally recommended for polyps that cannot be removed by simple polypectomy and when deep malignant invasion is not entertained.
"Although there are no hard-and-fast rules, we recommend EMR of complex colonic polyps in patients in whom the procedure can be performed safely, as assessed by the clinician, and in whom complete resection of the premalignant or early malignant lesion can be anticipated," says Suryakanth (Suryakanth Reddy) R. Gurudu, M.D., an endoscopist at Mayo Clinic's campus in Arizona.
EMR is appropriate for all noninvasive polyps of any size and for superficial T1a lesions with these characteristics:
- Diameter < 2 cm (which can be removed en bloc)
- Favorable histologic features, which suggest a low risk of lymph node spread, such as a well-differentiated grade of tumor, limited invasion into the submucosal layer (< 1,000 µm) and lack of lymphovascular invasion
Characteristics that make a lesion unsuitable for EMR include evidence of deep invasion, such as induration, ulceration, and the nonlifting sign in the absence of prior biopsy or cautery use during submucosal fluid injection.
"Experienced operators can use EMR to remove large lesions, with 30 to 75 percent of luminal circumference involvement, depending on the location," says Louis M. Wong Kee Song, M.D., a therapeutic endoscopist at Mayo Clinic's campus in Minnesota. This would include lesions in the right colon and rectum."
Lesions extending over haustral folds can be excised endoscopically by more experienced operators, depending on whether there is adequate submucosal lift. EMR can also be considered for lesions that involve to some extent the appendiceal orifice or ileocecal valve, but these require specialized techniques and expertise.
Which lesions are amenable to endoscopic submucosal dissection?
Originally pioneered in Japan for the treatment of early gastric cancer, endoscopic submucosal dissection (ESD) has since been applied to the treatment of large sessile and flat neoplastic colonic lesions. Given its labor-intensive nature and technical complexity, ESD should be reserved for lesions where there is clear clinical benefit.
"ESD is most beneficial for lesions with proven or suspected early invasion, including T1sm1 lesions, lesions with a diameter of 2 centimeters or more, and superficial T1b lesions. Sm2 or deeper lesions typically require surgical excision," advises Michael B.Wallace, M.D., a gastroenterologist specializing in advanced therapeutic endoscopy at Mayo Clinic's campus in Florida.
Endoscopic submucosal resection
Endoscopic submucosal dissection. A. Large distal rectal polypoid lesion. B. Marking of lesion boundary with coagulation dots. C. Post ESD defect. D. En bloc resected specimen.
ESD uses an electrosurgical cutting device or knife to dissect the deeper layers of the submucosa to remove neoplastic mucosal lesions. This approach facilitates en bloc resection of large lesions, which are generally amenable only to piecemeal resection by EMR. In addition to allowing for accurate histologic evaluation, en bloc resection is associated with a lower recurrence rate when compared with piecemeal resection by EMR.
Who should treat complex polyps?
Complex polypectomies require experienced endoscopists, appropriate accessories and knowledgeable support staff. Current research data suggest that in experienced hands, endoscopic resection of complex polyps results in improved morbidity and mortality, and a reduction in medical costs.