Adenomatous Polyps

Definition, Etiology, PathogenesisTop

Adenomatous polyps (the most common type of colorectal polyps in adults) are neoplasms characterized by hyperplasia and dysplasia of glandular epithelial cells, either low grade or high grade. If cells with high-grade dysplasia cross the muscular layer of the mucosa and infiltrate the submucosa, the condition qualifies as invasive cancer (ie, malignant polyp).

All adenomas have potential for malignant transformation. Histologic subtypes:

1) Tubular adenomas (comprise 65%-80% of removed polyps; characterized by branched tubular glands on histologic examination).

2) Villous adenomas (comprise 5%-10% of adenomas; characterized by long fingerlike projections of the surface epithelium on histologic examination).

3) Tubulovillous adenomas (comprise 10%-25% of adenomas; share the features of tubular and villous adenomas).

The risk of malignancy increases with size (>10 mm), gross shape (sessile), histologic type (villous), and grade of dysplasia (high). For example, tubular adenomas <10 mm have a <5% incidence of carcinoma, while villous adenomas >20 mm have a 50% incidence of containing a cancer. All adenomas should be excised, and subsequent surveillance is based on the presence of high-risk features (Table 1 in Colorectal Cancer Screening).

Clinical Features and Natural HistoryTop

Many polyps, especially those <1 cm in diameter, are asymptomatic. Symptoms associated with larger polyps may include occult bleeding into the lumen of the large intestine (usually latent; apparent in larger, distal polyps), anemia, sensation of fullness or pressure in the rectum (tenesmus; for polyps located in the rectum), or mucus in stool (villous adenoma). Very large polyps may be associated with an alteration in bowel habits and rarely with intermittent obstruction or intussusception. Large villous polyps may also be associated with watery (secretory) diarrhea (McKittrick–Wheelock syndrome). The risk of cancer in an adenoma depends on its diameter, shape, and histologic features. Classifications that estimate the likelihood of cancer being present in a polyp include the Kudo classification and Narrow-Band Imaging International Colorectal Endoscopic [NICE] classification.

DiagnosisTop

Diagnosis is usually established with colonoscopy (sensitivity >90% for polyps ≥7 mm in diameter) or computed tomography (CT) colonography (sensitivity 90% for lesions >1 cm in diameter). Histologic examination of a completely removed lesion enables determination of the polyp type (neoplastic invasive, neoplastic noninvasive, nonneoplastic).

TreatmentTop

Finding a polyp of the large intestine is an indication for its removal with subsequent histologic examination.

Endoscopic resection: There are a number of different endoscopic options for managing polyps, and the optimal approach is dependent on polyp size, shape, and presumed histologic features.

Simple endoscopic polypectomy with a diathermy loop and no electrocoagulation (ie, cold snare) is usually satisfactory for sessile polyps with a diameter <10 mm. It is acceptable to remove polyps ≤3 mm with biopsy forceps, but only if they fit completely in the forceps’ blades and can be removed en bloc.

Sessile polyps sized 10 to 19 mm in diameter and pedunculated polyps with a diameter of stalks <10 mm and heads <20 mm should be removed with a diathermy loop using electrocoagulation (ie, hot snare).

If the diameter of the polyp head is ≥20 mm in the pedunculated polyp or the diameter of the stalk is ≥10 mm, injection of epinephrine solution into the base of the polyp and/or application of mechanical hemostasis techniques to the base of the polyp (ie, clipping) are indicated before removal to prevent bleeding.

Large flat lesions require specific techniques (endoscopic mucosal resection [EMR] or endoscopic submucosal dissection [ESD]). It is recommended that the sites of removal of polyps concerning for potential invasive neoplasia (eg, NICE III, Kudo IV) or those removed in piecemeal using techniques such as EMR and ESD should be marked with an endoscopic tattoo (eg, India ink) to enable checking for recurrence during subsequent endoscopic examinations. Endoscopic tattooing is also useful for locating the area of concern in the operating room at the time of an oncologic resection (if required).

If a focus of invasive adenocarcinoma is found in the submucosa of a polypectomy specimen, oncologic resection may be indicated based on patient and disease factors. Malignancies without any high-risk features increasing the risk of lymph node metastasis that have been resected en bloc to negative margins (ie, >1 mm of the uninvolved tissue between the edge of specimen and disease) may be managed with endoscopic polypectomy. Factors that increase the risk of lymph node metastasis (up to 20%) and thus may prompt further management by way of oncologic resection include moderate-to-poor differentiation, tumor budding, lymphovascular invasion, perineural invasion, and deep submucosal invasion. If these factors are present and the patient is an appropriate operative candidate, segmental resection of the large intestine with removal of the surrounding lymph nodes (ie, radical oncologic resection) is generally recommended.

Surveillance After PolypectomyTop

According to the European Society of Gastrointestinal Endoscopy (ESGE) and American Society for Gastrointestinal Endoscopy (ASGE) guidelines, after the first colonoscopy with polypectomy, polyps are categorized as low risk or high risk, depending on their potential for malignant transformation. Surveillance algorithms provided by these guidelines vary slightly.