A 50-year-old male undergoes routine screening colonoscopy. A 1.5 cm pedunculated polyp in the sigmoid colon is completely excised. Histopathological examination demonstrates high-grade dysplasia with adenomatous tubules and finger-like projections. What histological subtype carries the highest risk of malignant transformation?
Answer and explanation
Correct answer: C. Villous adenoma
- Step 1: Colorectal adenomas are classified as tubular, tubulovillous, or villous based on glandular architecture.
- Step 2: Villous adenomas have the highest potential for malignant transformation (up to 40% in polyps > 2 cm) compared to tubular adenomas.
Answer
Villous adenoma.
Why not the others: 'Tubular adenoma' has a significantly lower malignant potential (approximately 5%); 'Hyperplastic polyp' is a non-neoplastic serrated lesion with minimal malignant risk when small and distal; 'Inflammatory pseudopolyp' is benign regenerative tissue seen in chronic colitis.
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