Colon Polyps Summary

By Zoe Z.

跟何老师病理实习刚结束，这一周在Z 医生的胃肠诊所就刚好经历了一位病人从初诊到内镜下发现 pedunculated and sessile polyp 的过程，结合临床和病理学习做了总结如下：

Case presentation

A 60 yo female complains of bright red rectal bleeding for 5 months. The bleeding was intermittent and occurred with bowel movement in moderate amount. She had rectal pain with defecation and the pain resolved spontaneously afterwards. She had history of constipation for 2 years but had one or two bowel movement every day recently. She had dizziness and short of breath occasionally, but CBC results two weeks ago were WNL. She had no fever, chills, nausea, vomiting, no recent weight loss, no change in appetite and diet. She had a balanced diet with vegetables, fruit and meat.

PMH: hypercholesterolemia.

PSH: two cesarean sections 30 and 25 years ago. Hemorrhoids resection 15 years ago

Medications: Statin, NSAIDS.

Allergies: NKDA.

The patient was scheduled for colonoscopy. Two polyps were found. One is a pedunculated polyp 3cm*1cm at descending colon, resected under the colonoscopy;another is a sessile polyp 3.5cm*3cm with irregular contour and superficial bleeding. Resection was attempted but not completed due to the large size. The patient was scheduled for repeat resection in the hospital. The biopsies were taken and sent for pathology examination.

Introduction

A polyp of the colon is a tumorousmass that protrudes into the lumen above the surrounding colonic mucosa. Theymay appear as sessile lesions without a definable stalk, or they may form as astalked or pedunculated polyp. Based on the malignant potential, Colon polypscan generally be classified as non-neoplastic which do not have the malignantpotential, including inflammatory polyps and hyperplastic polyps; andneoplastic polyps with adenomatous polyps or adenomas comprising approximatelytwo thirds of all colon polyps.

Clinical features

Colon polyps are usually asymptomatic, but sometimes they may ulcerate and bleed,causing tenesmus or intestinal obstruction if large. The polyps including adenomas are most commonly detected by colon cancer screening tests. The growth rates of different types of polyps, or even the same type of polyps vary significantly. However, complete regression is uncommon.

Endoscopic presentation and classification

Adenomas may be pedunculated, sessile, flat, excavated, or depressed based on their gross appearance under the endoscopy. The pedunculated polyp has a narrow base, with a mucosal stalk between the polyp and the wall. For the sessile polyps, the base and top of the lesion have the similar diameter. Regardless of the gross morphology, there are several endoscopic features suggestive of invasive cancer, including friability, ulceration and induration. A firm consistency or adherence of the polyp to the underlying tissue is also a concerning feature for malignancy.

Histological presentation and classification

1. Hyperplastic polyp

Hyperplastic polyps are the most common non-neoplastic polyps in colon. They are typical located in the rectal-sigmoid colon. Hyperplasic polyps are white or bland lesions. They usually present as small nodules (< 5mm in diameter) with nipple-like, hemispheric and smooth appearance, but can be large up to 2cm in diameter.

Three histologic subtypes have been described, including microvesicular, goblet cell, and mucin depleted. The prominent feature of the hyperplastic polyp as a non-neoplastic polyp is the normal architecture and proliferative characteristics with no dysplasia. Maturation occurs towards the surface, which is in contrast with adenoma where dysplasia appears on the surface and extends down the crypt. The epithelial cells pile on the surface along the length of the crypt, creating a serrated, longitudinal profile and star-shaped lumen in cross sections. The glands have an increased number of goblet cells and therefore look pale or cleared out next to normal epithelium. A polyp with adenomatous-looking cells at the base of the crypts, and frilly hyperplastic cells at the surface, is still a hyperplastic polyp.

2. Sessile serrated polyp

Sessile serrated polyp usually has a smooth surface, often flat or sessile, and may be covered with mucus. Recently,large (>1cm) hyperplastic polyps occurring in the right colon were recognized as a distinct subtype of polyp with malignant potential, associated with the microsatellite instability (as in hereditary nonpolyposis colorectal cancer [HNPCC]) cancer pathway. They are called either sessile serrated adenomas or sessile serrated polyps. It basically presents with the architecture of hyperplastic polyp but with dysplasia. Dysplasia may range from subtle to high-grade. Nuclear detail, number and location of mitotic figures is necessary for diagnosis.

The crypts have characteristic dilation and branching at the base (“duck feet”), and the epithelial cells maybe more eosinophilic (less mucin) and pseudostratified than the usual hyperplastic polyp. However, mature goblet cells and the frilly surface are still evident.

The difference is in the depth of proliferation: hyperplastic polyps show mostly surface hyperplasia and expansion, whereas the sessile serrated group is hyperplastic right down to the base. These are important to recognize, because they should be treated clinically like an adenoma, not just a hyperplastic polyp.

3. Adenomas

An adenoma (at least in the tubular-to-villous family) is defined as a polyp with low-grade dysplasia. Low-grade dysplasia in the colon indicates a cytologic change and stands out from normal colon as looking blue on the slide. Dysplasia begins abruptly on or near the surface and grows along crypts toward the base. The cells lining the crypts and the surface become tall and dark (because of depleted mucin) and have cigar-shaped and/or pseudostratified hyperchromatic nuclei. Mitoses may be present but are generally not apical.

In tubular adenomas, dysplastic epithelium spreads downward and the surface remains relatively smooth. Villous adenomas grow on delicate stromal fronds. Tubulovillous adenomas display combinations of these architectural patterns, with villous sand tubular components accounting for more than 20% of the polyp. The greater the villous component, the greater the tendency for malignant change.

Management, prognosis and surveillance of different types of polyps

1. Hyperplastic polyp

Although small rectosigmoid hyperplastic polyps do not appear to increase the risk of colorectal cancer, Small hyperplastic polyps are typically biopsied or removed during endoscopy with biopsy forceps because they can be difficult to differentiate from adenomatous polyps based on the appearance.

Surveillance colonoscopy is recommended in 10 years in the U.S. for patients with small (<10mm) hyperplastic polyps confined to the rectum or sigmoid colon.

2.  Sessile serrated polyp

Sessile serrated polyps with foci of dysplasia are considered the likely precursor lesions to sporadic microsatellite instability-high colon cancer. It is believed that a molecular pathway with a high frequency of methylation of CpG islands is involved. In particular, lesions with size more than or equal to 10mm, located in the proximal colon or with the presence of dysplasia possess higher risk for asynchronous advanced adenoma.

Due to the malignant potential it carries, this type of polyps is managed clinically like adenomatous polyps and complete excision is recommended. Considering its indistinct border, it is important to make sure the complete removal during the endoscopy procedure.

Patients with size of the polyp less than 10mm AND with no dysplasia are surveyed with colonoscopy in five years, similar to low risk adenomas. Whereas patients with size of the polyp larger than or equal to 10mm or with dysplasia are screened by colonoscopy every three years, as to the management of high-risk adenomas.

3.  Adenomatous polyp

Only a small minority (less than 5%) of adenomas progress to cancer over 7 to 10 years. In general, the risk of progression is higher for advanced adenomas with high grade dysplasia, more than 10 mm in size, or with a villous component.

In principle, adenomas should be resected completely. Small adenomas may be removed by biopsy forceps. For larger adenomas, snare resection with or without electrocautery or other advanced endoscopic resection may be required. If endoscopic resection is not possible,surgical resection is required.

Surveillance depends on the comprehensive evaluation of the risk of the adenoma. For low-risk adenomas, that is, only one or two small (<10mm) tubular adenomas found by colonoscopy, the first surveillance colonoscopy should be performed in 5 to 10 years. On the other hand, patients with an advanced adenoma or 3-10 adenomas found on colonoscopy, the first surveillance should be performed in three years. Patients with more than 10 adenomas should be screened in less than three years, and meanwhile must be evaluated for a hereditary colorectal cancer syndrome.

2/12/2018 于美国纽约

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