Imaging liver metastases: current limitations and future prospects

The diagnosis of liver metastasis relies on imaging. The sensitivity of ultrasound, CT and magnetic resonance techniques for detecting liver metastases can only be assessed in comparison with surgical inspection, intraoperative ultrasound and pathological examination, all methods that are of uncertain accuracy in detecting very small lesions. With current imaging technology, we should detect virtually all liver metastases 2 cm or larger in size, and most of those 1-2 cm in size. Even with optimum imaging, at present we detect only about one-half of metastatic nodules smaller than 1 cm in patients undergoing liver resection and pathological correlation. Improvements in the earlier detection of metastases will probably require a fundamentally different approach from that of conventional anatomical methods. Micrometastases produce alterations in blood flow that may be recognized by radionuclide or Doppler perfusion methods.