7. Diverticulosis of the colon. Pathology of colonic polyps

Written by ms. worldwide, edited by Nikolas.

Diverticulosis and diverticular disease

Introduction and epidemiology

A colonic diverticulum is a sac-like protrusion of the colonic wall. These diverticula are false diverticula (pseudodiverticula), due to how they involve only the mucosa and submucosa, and not the other layers of the colonic mucous membrane. The presence of many diverticula is called diverticulosis. In some cases, the diverticula may become inflamed. This conditition is called diverticulitis and occurs in approx 10% of people with diverticulosis.

Diverticulosis is usually asymptomatic, but it may cause symptoms like abdominal pain or lower GI tract bleeding. Diverticular disease refers to symptomatic diverticulosis or diverticulitis.

Diverticular disease is mostly a disease of elderly. 60% of people at the age of 60 have diverticulosis. Diverticulosis and diverticular disease is more common in the West, likely due to our eating habits. In the Western world, diverticulosis predominantly affects the left colon, while in Asia, it predominantly affects the right colon.

Etiology and pathomechanism

Colonic diverticula develop under conditions of high intraluminal pressure in the sigmoid colon, and since the colon has the muscle layer gathered at some places as teniae coli, this increased pressure may result in diverticula in these weaknesses where the muscle isn’t present. Exaggerated peristaltic contractions due to diet low in fibre may lead to high luminal pressure. In the western countries, as many as half of the population over 60 years may have this, while the prevalence in Japan and developing countries is much lower. This difference is due to the reduced fibre intake in the well-developed countries.

To avoid the development of diverticulosis, its recommended to eat dietary fibre (fresh fruits and vegetables, pasta etc.) and to change the way of sittin’ on the toilet (see the figure below).

The vessels of the diverticula become stretched and therefore weakened, which predisposes to the bleeding which presents are diverticular bleeding.

Diverticulitis occurs due to micro- or macroscopic perforation of a diverticulum, due to erosion of the diverticular wall by increased pressure and food particles. The perforation is usually contained by pericolic fat and mesentery, causing only a simple localised inflammation (simple diverticulitis). However, in some cases, a localised abscess, obstruction, large perforation or fistula may occur (complicated diverticulitis), which may lead to peritonitis.

Polyps of the colon and rectum

Introduction

Colonic polyps are elevated protruding lesions of the colon into the colon lumen. They may be hyperplastic, inflammatory, hamartomatous, or neoplastic. These polyps may cause symptoms or develop into cancer. >90% of colorectal cancers develop from an adenomatous polyp, but only 3 – 5% of adenomatous polyps progress to cancer.

Colon polyps are very common, affecting 30% of adults >50 years.

Classification

Non-neoplastic polyps
- Inflammatory polyps (pseudopolyps)
- Hyperplastic polyp
- Mucosal polyp
Neoplastic polyps
- Adenomatous polyps (colorectal adenoma)
- Serrated polyps
  - Sessile serrated polyp
  - Traditional serrated polyp
- Hamartomatous polyps

Colonic polyps can also be classified according to their macroscopic appearance:

Pedunculated – have stalk
Sessile – no stalk

Etiology

Colonic polyps are highly related to the Western, obesogenic lifestyle.

Diet high in meat and low in vegetables and fruits
Obesity
Lack of exercise
Smoking
Alcohol
Hereditary polyposis syndromes
- Familial adenomatous polyposis (FAP) and Gardner syndrome – for adenomatous polyp
- Juvenile polyposis syndrome and Peutz-Jeghers syndrome – for hamartomatous polyp

Inflammatory polyp

Inflammatory polyps are consequences of mucosal ulceration and regeneration, often present in IBD. They don’t have malignant potential.

Hyperplastic polyps

Hyperplastic polyps are consequences of idiopathic mucosal hyperplasia. Mucosal polyps have similar histology as normal mucosa, but often with more goblet cells. Neither have malignant potential.

Adenomatous polyps

Adenomatous polyps, also called colorectal adenomas, are the most important form of polyp, as they have the highest malignant potential, from 5 – 50% depending on subtype, and they’re the most common.

They are characterized by epithelial dysplasia, and these neoplastic mass lesions can range from small pedunculated polyps to large sessile lesions. As many as 50% of the western population over 50 years have these polyps, and since they are known to develop into malignancies, screening should be mandatory when you reach 50 years.

The morphology of the colorectal polyps varies, and they can be:

Pedunculated, having a stalk with vessels supplying it
Sessile, having a broad base
Semisessile, a mix between the two.

More about the morphology of the colorectal polyps can be studied in the slide section.

The following factors indicate a higher malignant risk for adenomatous polyps:

Multiple
Large (>2 cm)
Sessile morphology
Villous histology
High grade of dysplasia

Familial adenomatous polyposis (FAP) is an autosomal dominant and caused by the mutation of the adenomatous polyposis coli gene, APC. This disease manifests with hundreds to thousands(!!) polyps in the colon and rectum and start to appear already in the teenage years. They are actually morphologically indistinguishable from colorectal adenomas, so the only way to diagnose a patient with FAP is to count that more than 100 polyps are present.

If a patient with FAP doesn’t get treatment, this patient actually has 100% risk of developing a colorectal adenocarcinoma! And as that isn’t enough, FAP also has different variants like Gardner syndrome and Turcot syndrome.

All patients with FAP must their colon removed to prevent cancer.

Colonoscopy of a patient with FAP. We can see the high number of polyps.

Serrated polyps

Serrated polyps have a characteristic “sawtooth” morphology, which is the etymology of their name. They have moderate malignant potential (5%).

Hamartomatous polyps

Hamartomatous polyps are comprised of normal tissue but with disorganised growth. They may be idiopathic or develop in associated with a syndrome like juvenile polyposis syndrome or Peutz-Jeghers syndrome. Sporadic hamartomatous polyps have no malignant potential, but syndromic hamartomatous polyps do.

Macroscopically, they are pedunculated, round and lobulated. They may also be eroded. Histologically we can see branching and cystically dilated crypts.

Peutz-Jeghers syndrome is a rare autosomal dominant disorder and is characterized by hamartomatous polyps in the whole GI-tract, and mucocutaneous hyperpigmentation. The syndrome also carries higher risks for many malignancies, like breast-, colorectal-, pancreatic-, ovarian-, lung- and stomach cancers. Although the polyps mainly appear in the intestines, they can also occur in the stomach or in the lungs.