Imaging in Colorectal Cancer

Abstract

Imaging plays a pivotal role in the preoperative staging of malignant colorectal cancer. Multidetector computed tomography (CT or MDCT) is the principal investigation in the staging of colon cancer while both CT and magnetic resonance imaging (MRI), for local staging, have roles in the staging of rectal cancer. The introduction of CT colonography (CTC), also known as virtual or CT colonoscopy, has increased the sensitivity of CT in detecting small tumors and polyps. This clearly has implications in the screening of both symptomatic and asymptomatic populations. Though MRI and CT scanning are the main tools for staging colorectal cancers, other imaging modalities may be occasionally used. Endoscopic ultrasound (EUS) can be used to locally stage rectal tumors in certain cases, and EUS+FNA (fine needle aspiration) may be employed to determine nodal involvement. Positron emission tomography combined with CT (PET-CT) does not have a routine use in the staging of colorectal cancer but may be used for problem solving and detecting recurrent disease. In staging liver metastases, both MRI scanning (using liver-specific contrast agents) and contrast-enhanced ultrasound have roles. Double-contrast barium enema (DCBE) is still in use but is being replaced by CTC due to its greater accuracy (see below). Single contrast enema studies may still play a role in large bowel obstruction but have been largely replaced by MDCT [1].