Colonic polyps

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.

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

Classification and subtypes

• 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

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

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.

Clinical features

Colonic polyps are mostly asymptomatic, detecting during routine screening for colorectal cancer. If they cause symptoms, they cause:

• Haematochezia or occult blood loss
• Change in bowel habits

Diagnosis and evaluation

Some have occult blood which can be demonstrated in the faeces.

Colonoscopy is the best examination for polyps, as it allows for visualisation of even small polyps and for biopsy. Virtual colonoscopy, a CT examination of the colorectum insufflated with air and contrast, can be used as an alternative, but biopsies can not be made, and small (<1 cm) polyps cannot be visualised.

Treatment

If polyps are symptomatic or have significant malignant potential (e.g. in case of many large adenomatous polyps), removal is indicated. This can be performed by endoscopic or surgical resection. Some hereditary polyposis syndromes like FAP require prophylactic colectomy to avoid development of colorectal cancer.

Following polypectomy, regular surveillance colonoscopy is indicated based on the pre-treatment risk for malignant transformation, and whether removal was complete or not.