Malignant Polyps

Mucosectomy

The risk of malignancy increases with increased polyp size, proportion of the adenoma's villous components, and degree of dysplasia. The deciding factor is whether the muscle layer has been infiltrated, which signals lymphatic infiltration. If malignancy is first diagnosed during histological evaluation of a polyp that was not biopsied prior to removal, histopatholologi-cal stage determines further procedures. Resection of a malignant polyp with a healthy margin and which is in stage pT1 with a differentiation grade of G1 or G2 and without vessel infiltration (pT1 carcinoma: "low risk") is followed by curative endoscopic therapy. Lymphatic proliferation is not a major concern, particularly for malignant components in the proximal portion of the polyp at a good distance from the smooth muscle layer.

Patient age and health status determine whether resection of a malignant polyp (confirmed with biopsy) should be endoscopic or surgical. For routine resection of histologically confirmed malignant polyps, submucosal injection to elevate the polyp is indicated, especially for sessile polyps. Easily lifted malignant polyps are a sign of superficial infiltration of the bowel wall; complete removal of the malignancy with a margin of healthy tissue can be expected. If the polyp is not elevated by submucosal injection, the tumor is presumably fixed to the colon wall and the depth of infiltration makes complete removal with a healthy margin difficult. Though submucosal injection theoretically would entail a risk of spreading tumor cells in or through the bowel wall, findings are uncertain. It is vital that resection site of a malignant polyp is marked cor-rectly—e.g., by marking the coagulated base of a resected polyp with a needle—so that the pathologist can determine invasion depth.

Indications and contraindications. Mucosal resection is indicated for superficial carcinomas or flat adenomas that cannot be resected using conventional polypectomy techniques. If possible, endosonographic staging should be used prior to mu-cosectomy to ascertain depth of infiltration of the superficial carcinoma in the bowel wall (Fig. 18.15). Only those superficial carcinomas that are limited to the mucosa can be treated with endoscopic mucosal resection. If the tumor has infiltrated the submucosa, there is a risk of lymph node metastasis and thus surgical resection (lymph node dissection) is necessary. Table 18.2 shows the risk of lymph node metastasis related to mu-cosal and submucosal infiltration of superficial carcinomas (5,7).

Procedure. Mucosal resection is performed in the following steps (2, 4) (Fig. 18.16):

► Using an argon beam coagulator or polypectomy snare, the borders of the polyp or carcinoma are marked. If the borders are not clearly demarcated, chromoendoscopy with indigo carmine can be helpful for emphasizing the surface and margins.

► The lesion is injected with a mixture of 0.9% NaCl and diluted epinephrine (1:100000) or only 0.9% NaCl (Fig. 18.16b). Infiltration to the submucosa helps to lift the lesion (Fig. 18.6c), while the epinephrine allows the fluid cushion to remain longer in the submucosa. Injection volume depends on the size of the lesion, though usually at least 20 mL must be used. For larger flat polyps, a viscous solution of 0.5 % hyaluronic acid can be used (9). This solution is isotonic and is absorbed slowly so that the cushion can last for several hours, though the practicability of this technique needs further study.

► Mucosal resection of the lesion is performed with a monofilament polypectomy snare or special suction cap (straight or angled) and the corresponding asymmetrical snare (Fig. 18.16a, d). As the colon wall generally measures only 1.5-2.2 mm, the "suck-and-cut" technique using a special

Muscle layer Submucosa-Mucosa-

Endoscopic Submucosal Resection

Fig. 18.16 Schematic illustration of endoscopic mucosal resection using suction cap technique (modified based on 4). a Colonoscope with suction cap and asymmetrical snare. b Submucosal injection with NaCl solution and epinephrine. c Lifting the flat lesion after submucosal injection. d Suctioning the flat lesion into the cap and resection with a snare. e Recovering the resected lesion by suction into the cap.

Table 18.2 Lymph node metastases in superficial colon carcinomas related to depth of infiltration (5, 7)

Tumor stage

Frequency of

lymph node

metastasis

T1: Infiltration of mucosa

► m1: intraepithelial carcinoma

0%

► m2: infiltration of the lamina propria

0%

► m3: infiltration of the smooth muscle layer

0%

T1: Infiltration of submucosa

► sm1: upper third

2%

► sm2: middle third

up to 30%

► sm3: lower third

up to 30%

suction cap increases risk of perforation. For this reason, we choose not to use this technique at our clinic for mucosal resection in the colon.

► For larger lesions, it may be necessary to perform resection in several steps.

► Recovering resected material can be done with a polypectomy snare or by suction into the cap in the "suck-and-cut" technique (Fig. 18.16e).

► Possible complications (bleeding) are treated after recovering resected material. If bleeding is light or moderate, recovering resected material has priority.

► Using thin needles, resected material is spread out and fixated on cork, placed in a 10% formalin solution, and submitted for histological evaluation.

E 18.6 shows mucosal resection of a flat, broad-based polyp.

Mucosectomy of a superficial carcinoma is demonstrated in

- |T] 18.6 Steps in mucosal resection of broad-based polyps using piecemeal resection technique

- |T] 18.6 Steps in mucosal resection of broad-based polyps using piecemeal resection technique

Images Chromoendoscopy

c a-c Steps in mucosal resection of a broad-based flat polyp using piecemeal resection. Chromoendoscopy to better visualize borders. After injection, mucosal resection of the polyp using a snare. Smooth resection site.

Polyp Sigmoid ColonTypes Precancerous Colon Polyps Types Precancerous Colon Polyps

a-e Mucosal resection of a superficial carcinoma after submucosal injection. Histology showed an adenocarcinoma limited to the mucosa.

e a-e Mucosal resection of a superficial carcinoma after submucosal injection. Histology showed an adenocarcinoma limited to the mucosa.

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