Metastases and Recurrence of Colorectal Cancer: Diagnostic Role of Immunoscintigraphy

Abstract

Up to almost a half of all patients who undergo surgical resection of primary colorectal carcinoma can be expected to get recurrent or metastatic disease, predominatly within the first 2 postoperative years (Murphy et al., 1995). However, if the metastases and recurrences are identified before symptoms become evident, opportunities for a positive clinical outcome are enhanced. Barium enema examination and colonoscopy are two common modalities used in diagnosis of colorectal cancer, the latter being considered as a gold standard. Presently, advanced traditional and newly developed imaging techniques are also available. They are useful in staging the extent of such malignant tumors, including detection of their metastases and recurrences. Anatomical imaging techniques, such as ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI), are the ones mostly used. Thus, for local staging, superficial tumors are best staged using endorectal US, which also provides an assessment of the tumor ingrowth into the rectal wall layers. More advanced local tumors are best imaged using MRI. Computed tomography is not very accurate in early detection and differentiation of a recurrence of colorectal carcinoma due to distorted local anatomy after surgery as well as in the case of radiation changes. On the other hand, clinical value of virtual colonoscopy, performed by new generation of CTs is still under investigation. As far as prediction of nodal status is concerned, none of the three mentioned imaging modalities can be reliably used in clinical decision making. This is because many affected lymph nodes are bellow 1 cm in diameter; thus, explaining poor sensitivity of these techiniques. Only MRI using a lymph node specific contrast seems promising in the detection of nodal disease. For the detection of distant metastases transabdominal US is often the first choice for liver examination, and development of contrast agents for this technique has significantly increased its potentials in detecting focal liver lesions. Chest X-ray is also used as one of the primary diagnostic tools. However, multidetector CT is the mainstay of staging and follow-up of these patients, because it provides good coverage of the liver, the complete abdomen and the chest in one session. MRI is commonly used as the definitive imaging modality in detecting and characterizing liver lesions. 4 Metastases and Recurrence of Colorectal Cancer: Diagnostic Role of Immunoscintigraphy