The Utility of 18F-FDG-PET in the Diagnosis and Management of Colorectal Carcinoma

2-18F-fluoro-2-deoxyglucose-positron emission tomography (18F-FDG-PET) has gained wide acceptance as a clinical imaging tool in the evaluation of patients with colorectal carcinoma. Modern scanners consist of a hybrid system combining PET and computed tomography (CT) in one gantry (PET/CT). This provides more accurate assessment of both PET and CT images by allowing better localization of pathology and better discrimination of pathological tracer uptake from physiological tracer uptake. In addition the coregistered PET and CT images can be used to guide biopsy, thermal ablation techniques, and radiotherapy. 18F-FDG-PET has a high sensitivity for detection of metastatic disease. It is the imaging procedure of choice for accurate identification of patients who might be suitable for surgical resection of metastases. It is also accurate in discriminating fibrosis from active disease in patients who have undergone radiation therapy. It can help differentiate benign from malignant lesions such as hepatic lesions and pulmonary nodules and can be used to monitor the effectiveness of chemotherapy. It is also indicated for assessment of possible recurrence of disease in patients with a rising carcinoembryonic antigen. Although it does not replace traditional anatomic imaging techniques such as standard CT or magnetic resonance imaging, 18F-FDG-PET may be indicated in patients in whom there is a strong suspicion of metastatic disease despite negative conventional imaging. If done as the first line of testing in the context of increased tumor markers, 18F-FDG-PET can also guide the use of CT and magnetic resonance imaging to evaluate particular sites.