- Clinical science
Colonic polyps
Abstract
Colonic polyps are abnormal colonic mucosal overgrowths. They are a common finding in people over the age of 50. In rare cases, they may be seen in younger individuals as part of hereditary polyposis syndromes (e.g., familial adenomatous polyposis, Peutz‑Jeghers syndrome, etc.). On macroscopic examination, colonic polyps are either pedunculated (with a stalk) or sessile (without a stalk). Histologically, colonic polyps are most commonly adenomas (∼ 70%), followed by hyperplastic polyps, and, rarely, serrated polyps and hamartomatous polyps. Colonic polyps may be benign or have malignant potential. Adenomas have the highest malignant potential (5%) and most colonic carcinomas arise from them (adenoma‑carcinoma sequence). Most patients are asymptomatic, but they may present with altered bowel habits, blood/mucus in stool, and iron deficiency anemia. Colonoscopy is the diagnostic modality of choice, since it allows for direct visualization of the polyps, biopsy, and therapeutic snare polypectomy (of pedunculated polyps) or endoscopic submucosal resection (of sessile polyps). Large polyps (> 2 cm) or malignant polyps require surgical resection.
Epidemiology
- Incidence increases with age: ∼ 30% of individuals > 50 years .
-
Frequency
- ∼ 70% are adenomatous polyps
- ∼ 20% are hyperplastic polyps
- < 10% are other kinds of polyps (traditional serrated adenomas, sessile serrated adenomas, and mixed mucosal polyps).
- Sex: ♂ > ♀
References:[1][2][3]
Epidemiological data refers to the US, unless otherwise specified.
Etiology
- The exact etiology is unknown.
-
Risk factors
- Lifestyle
- Diet: high in red meat and fat; low in fiber and folic acid
- Obesity and lack of exercise
- Cigarette smoking
- Alcohol consumption
- Genetic predisposition
- Black populations
- Hereditary polyposis syndromes
- Lifestyle
References:[4]
Classification
Malignant potential | Histological type | Subtypes | Characteristics |
---|---|---|---|
Low malignant potential | . | Peutz-Jeghers syndrome Cronkhite-Canada syndrome |
|
Inflammatory polyps (pseudopolyps) |
| ||
Mucosal polyps |
| ||
Submucosal polyps |
| ||
Moderate malignant potential | Serrated polyps | Hyperplastic polyps Hyperplasia of normal cellular components and sawtooth/serrated pattern of crypt epithelium |
|
Sessile serrated polyps Morphology similar to hyperplastic polyps |
| ||
Traditional serrated adenoma Serrated architecture with dysplasia |
| ||
High malignant potential | Adenomatous polyps | Tubular adenoma Histology: proliferating cells form tubules |
|
Tubulovillous adenoma Histology: Mixture of tubular and villous histological picture |
| ||
Villous adenoma Histology: finger-like projections lined by dysplastic epithelium |
|
The majority of colon carcinomas develop from adenomas (adenoma‑carcinoma sequence). However, only ∼ 5% of adenomas develop into colon cancers!
Although villous adenoma is rarer than tubular adenoma, it has the highest malignant potential!
References:[1][2][5][6][7]
Clinical features
- Mostly asymptomatic
- If symptomatic
- Blood in stool (hematochezia) is the most common symptom.
- Change in bowel habits (constipation/diarrhea)
- Mucus in stool
- Physical examination
- Pallor
- Digital rectal examination: for rectal polyps
References:[1]
Subtypes and variants
Hereditary polyposis syndrome
- Adenomatous polyposis syndromes
- Hamartomatous polyposis syndromes
Adenomatous polyposis syndromes
Familial adenomatous polyposis (FAP)
-
Inheritance
- Mutation of the tumor suppressor gene APC (adenomatous polyposis coli)
- Autosomal dominant; (positive family history)
- Up to 25% of cases have a negative family history.
-
Epidemiology
- Occurs in one in 10,000–30,000 live births
- < 1% of colorectal cancers in the U.S. are due to FAP
- Both sexes equally affected
- Polyposis typically develops within the third decade of life
-
Clinical features
- Most are initially asymptomatic until progressing to colon cancer
- Altered bowel habits (constipation/diarrhea), blood in stool, and abdominal pain
- Congenital hypertrophy of the retinal pigment epithelium (CHRPE): multiple lesions in both eyes appearing in infancy
-
Diagnosis
- Flexible sigmoidoscopy/colonoscopy: > 100 polyps are typically detected in the classic FAP [8]
- Genetic testing: detection of germline mutations in the APC gene establishes the diagnosis [9]
- Histology: tubular, tubulovillous, and villous adenomas
- Desmoid tumors
- Treatment
- Prognosis: The lifetime risk of colorectal cancer is 100% by 45 years of age.
-
Variants of FAP
-
Attenuated FAP
- Lesser polyps (> 10 but < 100), mainly in the right colon
- More advanced age at presentation
- Lower risk (80%) of developing colorectal cancer than with classic FAP
-
Gardner syndrome
- FAP + extracolonic bony and/or soft tissue tumors (e.g., osteomas, desmoid tumors, sebaceous cysts, lipomas, fibromas)
- APC gene mutation with autosomal dominant inheritance
- The lifetime risk of developing colorectal cancer is 100%.
-
Turcot Syndrome
- Adenomatous colonic polyps + brain tumors
- Associated with FAP and Lynch syndrome
- Medulloblastomas are associated with FAP and gliomas with Lynch syndrome.
-
Attenuated FAP
Primarily hamartomatous
Peutz-Jeghers syndrome
-
Inheritance
- Autosomal dominant
- New mutations: 20% of cases
- Clinical features: 95% of patients have mucocutaneous hyperpigmentation that typically affects the lips (perioral lentigines), buccal mucosa, palms, and soles
- Enteroscopy: multiple hamartomatous polyps throughout the gastrointestinal tract
-
Prognosis
- The lifetime risk of colorectal cancer is ∼40%.
- Increased risk of ovarian, breast, and pancreatic cancer
Juvenile polyposis syndrome (JPS)
- Etiology: autosomal dominant with incomplete penetrance
- Clinical features: Onset is within the first decade of life, often with gastrointestinal bleeding and anemia
- Colonoscopy: > 10 polyps throughout the gastrointestinal tract
-
Prognosis
- Lifetime risk of colorectal cancer: 10–50%
- Increased risk of gastric cancer
Cowden syndrome
- Etiology: autosomal dominant (PTEN gene mutations)
-
Clinical features
- Multiple GI polyps + skin manifestations such as papules and hyperkeratosis of the skin and mucous membranes
- Changes in the thyroid and mammary glands: > 50% of patients have thyroid disorders (e.g., multinodular goiter, adenomas, etc.) and benign breast disorders (e.g., fibroadenomas, intraductal papillomas, etc.).
-
Prognosis
- Increased risk of colorectal cancer (up to 20%) before the age of 50
- Increased risk of breast, thyroid, endometrial, and renal cell carcinoma
Cronkhite-Canada syndrome
- Etiology: : probably immune-mediated (rare, nonfamilial disorder)
- Clinical features: GI polyposis with alopecia and cutaneous hyperpigmentation
- Treatment: immune suppression with glucocorticoids and azathioprine
- Prognosis: high mortality rate (50%) due to GI bleeding, sepsis, and congestive heart failure
MUTYH‑associated polyposis
-
Etiology
- Autosomal recessive inheritance
- Mutation in the MUTYH gene
- > 20 polyps
- Prognosis: The lifetime risk of colorectal cancer is 80–100%.
References:[2][9][8][10][11][12][13][14][15]
Diagnostics
-
Laboratory tests
- Fecal occult blood test
- Hemoglobin levels: Anemia
- Genetic studies: in patients with a strong family history of polyposis syndromes
-
Imaging
- Virtual colonoscopy:
- Air contrast barium enema: can detect left-sided colonic polyps
-
Flexible sigmoidoscopy
- Advantage: does not require extensive bowel preparation before the procedure.
- Disadvantage: The rest of the colon is not visualized.
-
Colonoscopy (confirmatory test)
- Preferred screening tool for diagnosed cases of hereditary polyposes/colonic cancer
- Advantages: Enables biopsy, histological confirmation, and therapeutic polypectomy (see “Classification” above)
- Disadvantages: Requires bowel preparation with laxatives; Risk of bowel perforation.
References:[1]
Treatment
Treatment depends on the etiology and nature of the polyp or polyps.
- Snare polypectomy: of pedunculated polyps (< 2 cm in size)
- Endoscopic mucosal resection: large sessile polyps
-
Surgical resection
- For large polyps (> 2 cm)
- For suspected malignancy: see colorectal cancer
- Hereditary polyposis syndromes
- For follow‑up, see colorectal cancer prevention.
References:[1][2]