## Investigation of Choice for Colorectal Cancer Diagnosis **Key Point:** Colonoscopy with tissue biopsy is the gold standard for diagnosis of colorectal cancer because it allows both visualization of the lesion and histopathological confirmation in a single procedure. ### Why Colonoscopy with Biopsy is Superior **High-Yield:** Colonoscopy offers: - Direct visualization of the entire colon and rectum - Ability to obtain tissue samples for histopathology (definitive diagnosis) - Therapeutic capability (removal of polyps, hemostasis) - Sensitivity >95% for lesions >1 cm - Allows assessment of synchronous lesions ### Role of Other Investigations | Investigation | Indication | Limitation | |---|---|---| | CT Colonography | Incomplete colonoscopy, strictures | No tissue diagnosis; radiation exposure | | Barium Enema | Contraindication to colonoscopy | No tissue biopsy; lower sensitivity for small lesions | | MRI Pelvis | Staging rectal cancer (T and N staging) | Not for primary diagnosis; expensive | **Clinical Pearl:** In this patient with a palpable rectal mass, colonoscopy is mandatory to obtain histological confirmation before any surgical planning. The proximity to the anal verge (6 cm) suggests rectal cancer, for which MRI pelvis would be the next investigation after diagnosis for staging purposes. **Warning:** Do not confuse diagnostic investigations with staging investigations. Biopsy confirms malignancy; imaging (CT, MRI) determines extent and resectability.
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