Imaging of liver metastases (CT scan, MRI, PET scan)

Abstract

The early detection of metastatic disease in colorectal cancer either at initial presentation or during follow up has been shown to benefit patients. This is because surgical resection for small volume isolated metastases can be curative and early detection of such disease improves the chances of cure. Even after metastatectomy, continued surveillance is worthwhile since repeat resection for recurrent disease is associated with favourable long-term survival [1−3]. The percentage of patients in whom long term cure is achievable following resection of metastatic disease in lungs or liver has increased in recent years and there is a continuing trend of improving survival and cure rates. Technological advances in imaging have played an important part in contributing to this improvement. This has been achieved through more accurate preoperative imaging leading to rigorous patient selection [4−6]. The relative merits of intensive image based follow up versus a less intensive method have been subject to debate. The evidence base however appears to favour more intensive follow-up. For example, a meta-analysis suggested that more intensive follow up combining CEA monitoring, outpatient clinical assessment and yearly CT scanning improves survival compared with less intensive follow up that does not utilise CT imaging [7]. The meta-analysis showed that intensive follow up was associated with a reduced time to first relapse and significant absolute reduction in mortality rate of 9−13%. Since these trials pre-dated the current wider trend of more aggressive hepatic resections and the use of combined therapies which, in their own right, have improved survival it is likely that the potential survival benefit from intensive follow up may be even greater than identified in the metaanalysis. The American Society of Clinical Oncology has made the following recommendations: – Annual computed tomography (CT) of the chest and abdomen for 3 years after primary therapy for patients who are at higher risk of recurrence and who could be candidates for curative-intent surgery – Pelvic CT scan for rectal cancer surveillance, especially for patients with several poor prognostic factors, including those who have not been treated with radiation – Colonoscopy at 3 years after operative treatment, and, if results are normal, every 5 years thereafter; flexible proctosigmoidoscopy every 6 months for 5 years for rectal cancer patients who have not been treated with pelvic radiation – History and physical examination every 3 to 6 months for the first 3 years, every 6 months during years 4 and 5, and subsequently at the discretion of the physician – Carcinoembryonic antigen every 3 months postoperatively for at least 3 years after diagnosis, if the patient is a candidate for surgery or systemic therapy – Chest x-rays, CBCs, and liver function tests are not recommended, and molecular or cellular markers should not influence the surveillance strategy based on available evidence. The liver is not only the most frequent site of metastatic disease but the sole site of metastasis in up to 30−40% of colorectal patients. Metastatic disease to the lungs occurs in (15%), followed by ovarian metastases (6−8%) [8], bones (5%) and brain. The spleen, kidneys, pancreas, adrenals, breast, thyroid and skin are rarely involved. In selecting patients for curative hepatic resection thin collimation CT or MR imaging of the liver with liver specific contrast agents are of critical importance in delineating the distribution of metastases and assessing overall resectability. MR imaging has a further important role to play in characterising coexisting benign lesions. In preoperative assessment of liver metastases, the following should be taken into account: – Accurate delineation of anatomical distribution of metastases and segmental sparing in patients undergoing hepatic resection – Confirmation of absence of widespread multi segmental micro metastatic disease within the liver – Confirmation of absence of extra hepatic disease – Discrimination between coexisting benign lesions and metastases