MALIGNANT FOCAL LIVER LESIONS

MALIGNANT FOCAL LIVER LESIONS - The ‘mass effect’
This term describes the effect of a focal mass, whether benign or malignant, on surrounding structures and is a useful diagnostic tool. It implies the lesion’s displacing or invasive nature, i.e. the displacement of vessels and/or invasion or distortion of adjacent structures and tissues as a result of the increasing bulk of a lesion. This effect differentiates a true mass from an infiltrative process such as steatosis, or an artefact. Masses which are large and/or closely adjacent to a vessel demonstrate the effect more readily. The mass effect does not, of course, differentiate benign from malignant masses, or help in any way to characterize the mass. It is particularly useful when the mass is isoechoic compared with normal liver. In such cases, the effect of the mass on adjacent structures may be the main clue to its presence.

Metastases
The liver is one of the most common sites to which malignant tumours metastasize. Secondary deposits are usually blood-borne, spreading to the liver via the portal venous system (for example in the case of gastrointestinal malignancies), or hepatic artery (for example lung or breast primaries), or spread via the lymphatic system. Some spread along the peritoneal surfaces, for example ovarian carcinoma. This demonstrates an initial invasion of the subserosal surfaces of the liver, as opposed to the more central distribution seen with a haematogenous spread. The former, peripheral pattern is more easily missed on ultrasound because small deposits are often obscured by near-field artefact or rib shadows. It is therefore advisable for the operator to be aware of the possible pattern of spread when searching for liver metastases.

Ultrasound appearances
The acoustic appearances of liver secondaries are extremely variable. When compared with normal surrounding liver parenchyma, metastases may be hyperechoic, hypoechoic, isoechoic or of mixed pattern. Sadly, it is not possible to characterize the primary source by the acoustic properties of the metastases. Metastases tend to be solid with ill-defined margins. Some metastases, particularly the larger ones, contain fluid as a result of central necrosis, or because they contain mucin, for example from some ovarian primaries. Occasionally, calcification is seen within a deposit, causing distal acoustic shadowing, and this may also develop following treatment with chemotherapy.

In some diseases, for example lymphoma, the metastases may be multiple but tiny, not immediately obvious to the operator as discrete focal lesions but as a coarse-textured liver. This type of appearance is non-specific and could be associated with a number of conditions, both benign and malignant. Diagnosis of focal liver lesions, such as metastases, is made more difficult when the liver texture is diffusely abnormal or when there are dilated intrahepatic ducts because the altered transmission of sound through the liver masks small lesions. Other possible ultrasound features associated with metastases include a lobulated outline to the liver, hepatomegaly and ascites. If the finding of liver metastases is unexpected, or the primary has not been identified, it is useful to complete a full examination to search for a sites of carcinomatous spread. Lymphadenopathy (particularly in the para-aortic, paracaval and portal regions) may be demonstrated on ultrasound, as well as invasion of adjacent blood vessels and disease in other extrahepatic sites including spleen, kidneys, omentum and peritoneum.

Doppler is unhelpful in diagnosing liver metastases, most of which appear poorly vascular or avascular. With the larger deposits, small vessels may be identified most often at the periphery of the mass. The use of microbubble contrast agents has been shown to improve both the characterization and detection of metastatic deposits on ultrasound. 8 The injection of a bolus of contrast agent when viewed using pulse-inversion demonstrates variable vascular phase enhancement with no contrast uptake in the late phase.

Clinical features and management of liver metastases
Many patients present with symptoms from their liver deposits rather than the primary carcinoma. The demonstration of liver metastases on ultrasound may often prompt further radiological investigations for the primary. The symptoms of liver deposits may include non-obstructive jaundice, obstructive jaundice (which may occur if a large mass is present at the porta), hepatomegaly, rightsided pain, increasing abdominal girth from ascites and altered LFTs.

Ultrasound-guided biopsy may be useful in diagnosing the primary and complements further imaging such as X-rays and contrast bowel studies. Accurate staging of the disease is currently bestperformed with CT or MRI, which have greater sensitivity for identifying small, sub-centimetre liver metastases, peritoneal deposits and lymphadenopathy and which can demonstrate more accurately any adjacent spread of primary disease. The prognosis for most patients with liver metastases is poor, particularly if multiple, and depends to a large extent on the origin of the primary carcinoma. A regime of surgical debulking(removal of the primary carcinoma, adjacent invaded viscera, lymphadenopathy, etc.) together with chemotherapy can slow down the progress of the disease. In an increasing number of cases, particularly those with metastases from a colorectal primary, which are less aggressive and grow more slowly, long-term survival can be achieved by resecting both the primary bowel lesion and then the liver deposits. The smaller and fewer the liver deposits, the better the prognosis. The success of this treatment has meant that tumours previously considered inoperable are now potentially curable. In such cases it is particularly useful to localize the lesions using the segmental liver anatomy prior to surgery. Intraoperative ultrasound (IOUS) is then used to confirm the preoperative appearances and examine the tumour margins to plan the line of resection.

Other methods of treatment include chemoembolization, and radiofrequency, microwave or laser ablation often under ultrasound guidance. The success of these options depends upon the number and size of the lesions, and the nature of the primary. Currently, these methods are considered palliative, rather than curative, and are an option for patients who are unsuitable candidates for hepatic resection.

Ultrasound of other relevant areas
In suspected or confirmed malignancy, the examination of the abdomen may usefully include all the sites likely to be affected. While the liver is one of the most common sites for spread of the disease, it is also useful to examine the adrenals, spleen and kidneys, and to look for lymphadenopathy in the para-aortic, paracaval and portal regions. If ascites is present, deposits may sometimes be demonstrated on the peritoneal or omental surfaces in patients with late-stage disease.