DIFFERENT IMAGING MODALITIES USED IN THE DETECTION OF COLORECTAL CANCER

An Evaluation Of The Different Imaging Modalities Used In The Detection Of Colorectal Cancer

Abstract

In the past 20 years, the radiology of colorectal cancer has evolved from the barium enema to advanced imaging modalities like phased array magnetic resonance imaging (MRI), virtual colonoscopy and positron emission tomography (PET). Nowadays, primary rectal cancers are preferably imaged with transrectal ultrasound or MRI, while barium enema is still the most often used technique for imaging of colonic cancers. Virtual colonoscopy is rapidly evolving and might considerably change the imaging of colorectal cancer in the near future. The use of virtual colonoscopy for screening purposes and imaging of the colon in occlusive cancer or incomplete colonoscopies is currently under evaluation. The main role of PET is in detecting tumour recurrences, both locally and distantly. Techniques to fuse cross-sectional anatomical (computer tomography (CT) and MRI) and functional (PET) images are being developed. Apart from diagnostic imaging, the radiologists has added image-guided minimally invasive treatments of colorectal liver metastases to their arsenal. The radio-frequency ablation technique is now widely available, and can be used during laparotomy or percutaneously in selected cases.

An Evaluation Of The Different Imaging Modalities Used In The Detection Of Colorectal Cancer

Radiology of colorectal cancer

Radiology of colorectal cancer has dramatically evolved over the past two decades. In the 1980s, colorectal cancer could be diagnosed with a barium enema, and its liver metastases with ultrasound (US) and incremental computer tomography (CT). Nowadays, there is a definite difference in the imaging approach of either colonic or rectal cancer. The method of choice for imaging of colonic cancer is still a double-contrast barium enema (DCBE), while rectal cancer is preferably imaged with transrectal ultrasound (TRUS) or magnetic resonance imaging (MRI). Both the use and clinical impact of DCBE and CT in the imaging of rectal cancer is limited nowadays. New imaging techniques for both colonic and rectal cancer are still evolving: virtual colonoscopy (CT- or MRI-based), positron emission tomography (PET), and the combination of PET and a cross-sectional technique like CT (image fusion). Colorectal liver metastases are imaged with US, MRI, helical or multi-detector CT and PET. MRI, helical or multi-detector CT and PET can also be used to image the direct extension, lymphatic spread and peritoneal seeding of colorectal cancer. Image-guided, minimally invasive treatment of colorectal liver metastases is another new component in the radiology of colorectal cancer.

The radiology of colorectal cancer is addressed in this review in four separate sections. In the first section, the various widely available diagnostic methods for imaging of primary colorectal cancer are reviewed. The second and third sections are on virtual colonoscopy, and PET and image fusion, respectively. The final part describes the image-guided treatment of colorectal liver metastases. The interaction of endoscopy and radiology in primary colorectal cancer, and the imaging of colorectal liver metastases are beyond the scope of this review.

Imaging of colorectal cancer

Introduction

Most, if not all, colorectal cancers develop via the adenoma-carcinoma sequence with an adenoma dwell time, in the ...