A 58-year-old man presents with a 3-month history of altered bowel habits, blood in stool, and weight loss. Digital rectal examination reveals a palpable mass 7 cm from the anal verge. Which investigation is most appropriate to confirm the diagnosis and assess local staging?

Explanation

## Investigation of Choice for Colorectal Carcinoma Diagnosis **Key Point:** Colonoscopy with tissue biopsy is the gold standard for diagnosis of colorectal carcinoma. It allows direct visualization, biopsy for histopathological confirmation, and assessment of synchronous lesions. ### Why Colonoscopy with Biopsy is Correct **High-Yield:** Colonoscopy provides: 1. Direct visualization of the lesion 2. Tissue diagnosis (histopathology) — essential for staging and grading 3. Detection of synchronous polyps or tumors (present in 2–5% of cases) 4. Therapeutic intervention if needed (polypectomy, stent placement) **Clinical Pearl:** In this patient with a palpable rectal mass, colonoscopy is both diagnostic and therapeutic. Biopsy confirms adenocarcinoma type, grade, and presence of mucinous differentiation — all critical for prognosis and treatment planning. ### Comparison of Imaging Modalities | Investigation | Role | Limitation | |---|---|---| | **Colonoscopy + Biopsy** | Diagnosis + tissue confirmation | Cannot assess distant metastases or depth of invasion | | **MRI pelvis (endorectal coil)** | Local staging (T, N) in rectal cancer | Requires diagnosis first; not for initial diagnosis | | **CT abdomen/pelvis** | Metastatic staging (M stage) | Poor visualization of primary tumor; not diagnostic | | **Barium enema** | Screening/surveillance (outdated) | No tissue diagnosis; poor sensitivity for small lesions | ### Diagnostic Algorithm ```mermaid flowchart TD A[Suspected colorectal cancer]:::outcome --> B{Clinical presentation?}:::decision B -->|Rectal mass on DRE| C[Colonoscopy + Biopsy]:::action C --> D[Histopathology confirms diagnosis]:::outcome D --> E[Staging investigations]:::action E --> F[MRI pelvis for rectal cancer<br/>CT chest/abdomen/pelvis for metastases]:::action F --> G[Treatment planning]:::outcome ``` **Mnemonic:** **SCOPE** — for colorectal cancer diagnosis: - **S**cope (colonoscopy) for visualization - **C**onfirm with biopsy - **O**ther lesions (synchronous tumors) - **P**athology (grade, type) - **E**xtent (staging after diagnosis) [cite:Robbins 10e Ch 17]