A 58-year-old man presents with profuse watery diarrhoea, weakness, and cramps. Serum potassium is 2.6 mmol/L. Colonoscopy reveals a large 5 cm sessile lesion in the rectosigmoid region. Which feature of this lesion best explains his biochemical abnormality?
- A Obstruction of the colonic lumen causing stercoral ulceration
- B Ectopic production of vasoactive intestinal peptide
- C Villous architecture secreting potassium-rich mucus ✓
- D Chronic occult blood loss through the lesion surface
Correct answer: C. Villous architecture secreting potassium-rich mucus
Explanation
Large villous adenomas of the distal colon and rectum secrete copious potassium-rich mucus, producing hypokalaemia, dehydration, and sometimes hyponatraemia and pre-renal azotaemia. This is a local secretory phenomenon, not a hormonal syndrome, so ectopic VIP production is incorrect. Occult bleeding causes iron deficiency anaemia rather than hypokalaemia, and luminal obstruction causes constipation, not secretory diarrhoea. Villous adenomas also carry the highest malignant potential among adenoma subtypes.
Reference: Schwartz's Principles of Surgery, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.