After a colonoscopy shows adenocarcinoma, which imaging study is used to assess abdominal involvement?

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

Answer: (B)

When staging colon cancer, you need detailed images of the abdomen to see how far the tumor extends, whether nearby lymph nodes are involved, and whether there are liver metastases. A contrast-enhanced CT scan of the abdomen (often including the pelvis) provides these cross-sectional views and is the standard initial imaging to assess abdominal involvement. It gives good resolution for the bowel wall, surrounding structures, and the liver, which is the common site of spread.

A PET scan can detect metabolically active disease and is useful in certain scenarios, such as evaluating suspected metastases when CT findings are unclear or for restaging after treatment, but it is not the first-line test for assessing abdominal involvement due to limitations in detecting small liver lesions and higher cost.

MRI of the brain isn’t routinely used for abdominal staging since brain metastases from colorectal cancer are uncommon, and a chest X-ray offers limited information about intra-abdominal disease, making CT abdomen/pelvis the most appropriate choice here.