Evaluation of the Liver for Metastatic Disease

Erik K. Paulson, MD1, 1Department of Radiology, Duke University Medical Center, Durham, North Carolina.

Semin Liver Dis. 2001;21(2) 

In This Article

Computed Tomography

As with ultrasound, the CT manifestations of metastatic disease are varied.[1] On precontrast scans, metastases are nearly always of decreased attenuation compared with the background liver, which is usually of relatively high attenuation due in part to the presence of glycogen within hepatocytes.

Precontrast CT is more sensitive than US for the detection of calcium within a tumor (Fig. 10). Calcifications may be psammomatous, which creates a stippled appearance or macroscopic dystrophic calcium, which in turn creates chunks of high attenuation. The identification of calcification may aid in the differential diagnosis for the patient who presents with a large heterogeneous hepatic mass. When calcification is present, the most likely diagnosis is a colon cancer metastasis. Treated metastases may also develop calcifications. Occasionally, the use of IV contrast will obscure the presence of calcifications.

Figure 10

Metastatic mucinous adenocarcinoma of the colon. A. Precontrast scan through the liver shows a mass that contains subtle areas of high attenuation centrally (arrow). This high attenuation is due to psammomatous calcifications within a metastasis. B. Image obtained during the portal predominant phase of enhancement shows the margins of the lesion to better advantage. Note that the calcification is not visible following the administration of contrast due to the enhancement of the tumor.

Figure 10

Metastatic mucinous adenocarcinoma of the colon. A. Precontrast scan through the liver shows a mass that contains subtle areas of high attenuation centrally (arrow). This high attenuation is due to psammomatous calcifications within a metastasis. B. Image obtained during the portal predominant phase of enhancement shows the margins of the lesion to better advantage. Note that the calcification is not visible following the administration of contrast due to the enhancement of the tumor.

After IV contrast has been injected, the appearance of metastases will vary based on vascularity of the lesion and timing of the acquisition (Fig. 11). Most metastases are relatively hypovascular compared with the background liver and will be of decreased attenuation on pre-contrast, arterial predominant phase, and portal venous predominant phase scans. Metastases that tend to be hypovascular include those from the colon, lung, prostate, and gynecological primaries.

Figure 11

Variable enhancement as demonstrated on dual-phase CT. A. Arterial predominant-phase CT shows a hyperenhancing nodule (arrow) in the liver. At this point, contrast is present in the aorta and hepatic artery branches but has not yet enhanced the liver parenchyma. B. On the portal venous predominant-phase imaging, the lesion is now of low attenuation compared with the background liver, which is at peak enhancement. Note the interesting rim of hyperenhancement surrounding the lesion that may represent compressed parenchyma or a rim of hypervascularity about the tumor.

Figure 11

Variable enhancement as demonstrated on dual-phase CT. A. Arterial predominant-phase CT shows a hyperenhancing nodule (arrow) in the liver. At this point, contrast is present in the aorta and hepatic artery branches but has not yet enhanced the liver parenchyma. B. On the portal venous predominant-phase imaging, the lesion is now of low attenuation compared with the background liver, which is at peak enhancement. Note the interesting rim of hyperenhancement surrounding the lesion that may represent compressed parenchyma or a rim of hypervascularity about the tumor.

Metastases with abundant arterial blood flow may enhance vividly during the arterial- predominant phase of enhancement (Fig. 12).[41,42,43,44] These include metastases from neuroendocrine tumors, phenochromocytoma, carcinoid, breast, renal cell carcinoma, and thyroid. In fact, these tumors are often most conspicuous during the hepatic arterial-predominant phase of enhancement, reflecting their increased arterial supply. During the portal venous predominant phase of enhancement, the lesions may be isodense to liver and difficult to detect. Indeed, there is the occasional patient with a hypervascular primary tumor in whom metastases will be entirely missed unless arterial predominant-phase imaging is performed. There is some debate as to which tumors are best imaged with the addition of arterial-phase imaging. Research suggests that metastases from neuroendocrine tumors, including carcinoid and thyroid, are extremely hypervascular and are best seen during the hepatic arterial phase of enhancement.[42,43] Other so-called hypervascular tumors may be less vascular, including metastases from renal cell carcinoma, breast carcinoma, and melanoma. In these tumors, the added value of the arterial phase is controversial, at least in terms of detection per se.

Figure 12

Triple-phase spiral CT in a patient with metastatic carcinoid tumor. A. A precontrast scan is unremarkable, failing to detect metastatic disease. B. During the arterial predominant phase of enhancement, multiple vividly enhancing hypervascular metastases are present. These lesions are best seen during this phase of enhancement. C. During the portal predominant phase of enhancement, the lesions are isodense to background liver and are difficult to detect. This case illustrates the value of arterial predominant-phase imaging in patients with hypervascular metastatic disease.

Figure 12

Triple-phase spiral CT in a patient with metastatic carcinoid tumor. A. A precontrast scan is unremarkable, failing to detect metastatic disease. B. During the arterial predominant phase of enhancement, multiple vividly enhancing hypervascular metastases are present. These lesions are best seen during this phase of enhancement. C. During the portal predominant phase of enhancement, the lesions are isodense to background liver and are difficult to detect. This case illustrates the value of arterial predominant-phase imaging in patients with hypervascular metastatic disease.

Figure 12

Triple-phase spiral CT in a patient with metastatic carcinoid tumor. A. A precontrast scan is unremarkable, failing to detect metastatic disease. B. During the arterial predominant phase of enhancement, multiple vividly enhancing hypervascular metastases are present. These lesions are best seen during this phase of enhancement. C. During the portal predominant phase of enhancement, the lesions are isodense to background liver and are difficult to detect. This case illustrates the value of arterial predominant-phase imaging in patients with hypervascular metastatic disease.

There is emerging data to indicate that in some metastases, the degree of vascularity may correlate with biological activity. If so, it may be necessary to report not only the size and number of lesions but also the presence of and changes in the degree of enhancement. This speculation awaits the results of scientific inquiry.

As with US, cystic metastases are uncommon by CT. Usually the presence of debris, thick septations, walls, or nodules will allow differentiation from simple benign cysts (Fig. 13).

Figure 13

Cystic metastases from carcinoid. CT scan shows multiple cystic metastases from carcinoid. The presence of fluid levels, thickened walls, mural nodules, and debris help differentiate cystic metastases from benign simple cysts.

A relative pitfall of CT is in the setting of diffuse disease, where CT may underestimate the extent of involvement. Clues to the presence of diffuse replacement of parenchyma by metastatic disease include hepatomegaly, a nodular capsular surface, and indistinct vascular margins.[1] Often, precontrast or arterial-phase imaging demonstrates diffuse disease better than portal venous-phase imaging alone (Fig. 14). If in doubt, MRI or biopsy will prove helpful.

Figure 14

Diffuse infiltration of the left lobe of the liver. A. Precontrast scan of the liver shows decreased attenuation of the left lobe due to diffusely infiltrating breast cancer. B. During the portal venous phase of enhancement, the diffuse disease is difficult to detect because it enhances similarly to that of normal hepatic parenchyma. The clues that diffuse disease is present include subtle nodularity (arrows) of the capsular surface and obscuration of blood vessels. In this case, the findings of diffuse disease are difficult to detect using portal venous phase imaging alone.

Figure 14

Diffuse infiltration of the left lobe of the liver. A. Precontrast scan of the liver shows decreased attenuation of the left lobe due to diffusely infiltrating breast cancer. B. During the portal venous phase of enhancement, the diffuse disease is difficult to detect because it enhances similarly to that of normal hepatic parenchyma. The clues that diffuse disease is present include subtle nodularity (arrows) of the capsular surface and obscuration of blood vessels. In this case, the findings of diffuse disease are difficult to detect using portal venous phase imaging alone.

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