Villous adenoma

Introduction

A villous adenoma is a type of adenomatous polyp found in the colon, characterised by finger-like (villous) projections on histology. These polyps are premalignant and carry a significantly higher risk of malignant transformation compared to other types, such as tubular adenomas.

Peak Incidence

• Most commonly seen in individuals aged over 60 years.

Pathophysiology

• Villous adenomas arise from dysplastic epithelial proliferation within the colonic mucosa.
• Their villous architecture increases surface area and secretory activity, explaining their association with mucus secretion and electrolyte disturbances.
• The risk of malignant transformation increases with size, degree of dysplasia, and the proportion of villous components.

Symptoms

• Asymptomatic – Many villous adenomas are discovered incidentally during screening colonoscopy.
• Symptomatic cases may present with:
  • Rectal bleeding – Most common presenting symptom.
  • Mucus discharge – Can lead to hypokalaemia and metabolic alkalosis due to excessive fluid loss.
  • Change in bowel habit – Constipation or diarrhoea.
  • Tenesmus – A sensation of incomplete evacuation.
  • Abdominal pain.
  • Weight loss – In cases of large or malignant lesions.

Signs

• Pallor – Due to iron-deficiency anaemia from chronic blood loss.
• Abdominal tenderness – If the lesion is large or causing partial obstruction.
• Palpable rectal mass – Detected on digital rectal examination if the lesion is low-lying in the rectum.

Diagnosis

Endoscopic Assessment

• Colonoscopy – Gold standard investigation.
  • Villous adenomas typically appear as:
    • Sessile (broad-based) lesions.
    • Velvety or cauliflower-like in appearance.
    • Often larger than tubular adenomas.

Histology

• Biopsy confirms villous architecture.
  • Histopathological analysis evaluates:
    • Degree of dysplasia.
    • Presence of invasive carcinoma.

Imaging

• CT colonography – Alternative if colonoscopy is incomplete or contraindicated.
• Barium enema – Rarely used; may show a non-specific filling defect.

Blood Tests

• Full blood count (FBC) – May reveal iron-deficiency anaemia.
• Urea & Electrolytes (U&Es) – Hypokalaemia in cases of excessive mucus loss.
• Venous blood gas (VBG) – May show metabolic alkalosis.
• Carcinoembryonic antigen (CEA) – Can be elevated if malignant transformation has occurred; not used for screening.

Complications

• Malignant transformation – Particularly in lesions >4 cm, with risk estimated up to 40%.
• Intestinal obstruction – Especially if large or involved in intussusception.
• Haemorrhage – From mucosal ulceration or vascular involvement.
• Rectal prolapse – Rare, but possible if the lesion is located in the distal rectum.

Management

Endoscopic Removal

• Polypectomy – Preferred method for small or pedunculated polyps.
  • Snare polypectomy – For pedunculated lesions.
  • Endoscopic mucosal resection (EMR) – For larger, sessile lesions.

Surgical Resection

• Indicated when:
  • Endoscopic removal is incomplete or not feasible.
  • There is high-grade dysplasia or invasive carcinoma on biopsy.
  • Lesion is large (>3–4 cm) or has sessile morphology with poor access.
  • There is evidence of obstruction or perforation.

Surveillance

• Repeat colonoscopy in 3 years for:

  • Large villous adenomas.
  • High-grade dysplasia.

• Repeat colonoscopy in 5 years for:

  • Smaller lesions with low-grade dysplasia.