If colonoscopy screening reveals adenocarcinoma, which imaging study should be ordered next to evaluate the extent of disease?

• A. PET scan
• B. MRI brain
• C. Chest X-ray
• D. CT scan of the abdomen

Answer: (D)

Staging is about determining how far the cancer has spread to guide treatment. For colon cancer, the most important initial imaging is a contrast-enhanced CT scan of the abdomen (often including the pelvis). This test shows the primary tumor’s local extent and, crucially, the liver and other abdominal metastases that are common in colorectal cancer. It provides detailed anatomic information to plan surgery and systemic therapy.

MRI of the brain is reserved for patients with neurologic symptoms or known brain involvement, not as routine initial staging. PET scans can be helpful in selected cases or for detecting occult metastases, but they aren’t the preferred first-line test for staging colon cancer because CT already gives the essential anatomic detail and is more widely used for initial staging. Chest X-ray is less sensitive for detecting metastases and does not adequately assess liver, peritoneal, or pelvic involvement.