Villous adenoma

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]; Tarek Nafee, M.D. [3]

Synonyms and keywords: Adenomatous polyps; VA; TVA

Overview

Villous adenoma (also known as adenomatous polyp) is a type of polyp that grows in the colon and other places in the gastrointestinal tract and may have a malignant (cancerous) transformation. Villous adenoma was first discovered by Helwig in 1946. According to the World Health Organization, villous adenoma can be classified into 3 groups: tubular, tubulovillous, and villous (most common). Villous adenoma arises from epithelial tissue, which is normally part of the lining of the colon. The estimated risk of malignancy among villous adenomas is between 15 and 25%. Genes associated in the development of villous adenoma, include: APC gene, TP53 gene, K-ras gene, and BAT-26 gene. The prevalence of villous adenoma is approximately 3.5 per 100,000 individuals worldwide. The most important risk factor in the development of villous adenoma is familiar syndromes (e.g. Turcot syndrome, juvenile polyposis syndrome, and Cowden disease). Surgical removal is the mainstay of therapy for villous adenoma. Cautery snare in conjunction with exploratory colonoscopy is the most common approach to the treatment of villous adenoma. Effective measures for the primary prevention of villous adenoma include periodical screening for patients with family history of familial adenomatous polyposis. According to the guidelines established by the American Cancer Society, individuals who reach the age of 50 should perform an occult blood test yearly.

Historical Perspective

Villous adenoma was first discovered by Helwig in 1946.

Classification

Villous adenoma may be classified according to the World Health Organization into 3 groups:

• Tubular
• Tubulovillous
• Villous (most common)

Pathophysiology

Pathogenesis

The pathogenesis of villous adenoma is characterized by: Villous adenoma arises from overgrowth of epithelial tissue with glandular characteristics.

Genetics

Genes associated with the development of villous adenoma include:

• APC gene
• TP53 gene
• KRAS gene
• BAT-26 gene

Gross Pathology

On gross pathology, characteristic findings of villous adenoma include:

• Polypoid or sessile mass
• Cauliflower-like in appearance

Microscopic Pathology

On microscopic histopathological analysis, characteristic findings of villous adenoma include:

• Nuclear changes at the surface of the mucosa
• Cigar-shaped (elongated) nucleus (length:width > 3:1) with nuclear hyperchromasia
• Large round nuclei
• Nuclear crowding
• Positive Ki-67

Causes

The most important cause of villous adenoma is familial adenomatous polyposis.

Differentiating Villous Adenoma from Other Diseases

• Villous adenoma must be differentiated from other diseases that cause abnormal growth of tissue projecting from a mucous membrane such as:

• Colorectal cancer
• Inflammatory fibroid polyp

Epidemiology and Demographics

Prevalence

The prevalence of villous adenoma is approximately 3.5 per 100,000 individuals worldwide. The prevalence of adenomas increases with age.

Age

Patients of all age groups may develop villous adenoma.

Gender

Males are more commonly affected with villous adenoma than females.

Race

Villous adenoma more commonly affects individuals of the Caucasian race.

Risk Factors

Common risk factors in the development of villous adenoma, include:

• Familial adenomatous polyposis
• Peutz–Jeghers syndrome
• Turcot syndrome
• Juvenile polyposis syndrome
• Cowden disease
• Bannayan–Riley–Ruvalcaba syndrome (Bannayan-Zonana syndrome)
• Gardner's syndrome

Natural History, Complications and Prognosis

Natural History

The majority of patients with villous adenoma remain asymptomatic for years. Early clinical features may include flatulence, bloating, and abdominal pain. If left untreated, patients with villous adenoma may progress to develop colorectal cancer.

Complications

Common complications of villous adenoma include:

• Bleeding
• Obstruction
• Bowel torsion

Prognosis

Prognosis is generally good and the 5-year mortality of patients with villous adenoma is approximately 89%. Prognosis becomes poorer with malignant transformation of the lesion. The estimated risk of malignant transformation of villous adenoma is from 15% to 20%.

Diagnosis

Symptoms

Villous adenoma is usually asymptomatic. Villous adenoma symptoms are often non-specific. Symptoms of villous adenoma may include:

• Flatulence
• Abdominal pain
• Constipation
• Diarrhea
• Cramping

Physical Examination

Patients with villous adenoma usually are well-appearing. Physical examination findings are often non-specific. Physical examination may demonstrate:

• Rectal bleeding
• Rectal mass
• Pencil-thin stools

Laboratory Findings

There are no specific laboratory findings associated with villous adenoma. In some cases, patients with villous adenoma may demonstrate hypokalemia.

Imaging and Diagnostic Findings

Colonoscopy is the diagnostic modality of choice for villous adenoma. On colonoscopy, characteristic findings of villous adenoma include:

• A sessile polyp
• Size can range from 0.5 cm to 5 cm

Other imaging studies include:

• Computed tomographic colonography
• Video capsule endoscopy (less specific)

Treatment

Medical Therapy

There is no treatment for villous adenoma; the mainstay of therapy is surgical removal.

Surgery

Surgical removal is the mainstay of therapy for villous adenoma. Colonoscopy is both diagnostic and therapeutic. Cautery snare in conjunction with exploratory colonoscopy is the most common approach to both the diagnosis and treatment of villous adenoma.

Prevention

Effective measures for the primary prevention of villous adenoma include periodic screening for patients with family history of familial adenomatous polyposis. According to the guidelines established by the American Cancer Society, individuals who reach the age of 50 should perform an occult blood test yearly, a colonoscopy every 10 years, or a flexible sigmoidoscopy every 3 to 5 years. Once diagnosed and successfully treated, patients with villous adenoma are followed-up every 12 to 24 months.