Clinical History
A 70-year-old man was admitted for investigation of muscular weakness and the passage of large amounts of mucus per rectum. The patient was found to be hypokalaemic. A tumour of the sigmoid colon was discovered and later resected.

Pathology
A 15 cm segment of colon has been opened longitudinally to reveal a large sessile tumour with a velvety surface. The tumour measures 11 × 7 cm and approaches within 2 cm of the distal resection margin. The rest of the mucosa appears normal. The serosal surface is unremarkable. Histological examination confirmed the presence of a villous adenoma.

Further Information
Villous adenomas can sometimes secrete large amounts of mucoid protein and/or potassium-rich fluid, which may cause hypoalbuminaemia or hypokalaemia, explaining the patient's symptoms of muscular weakness and mucus passage. Villous adenomas are the least common type of adenomatous polyp but are the most ominous due to their higher risk of malignant transformation. Up to 30% of villous adenomas have invasive carcinoma at the time of resection, underscoring the need for early detection and treatment.