Imaging of liver metastases: MRI

Abstract

Metastases are the most common malignant liver lesions and the most common indication for hepatic imaging. Specific characterization of liver metastases in patients with primary non-hepatic tumors is crucial to avoid unnecessary diagnostic work-up for incidental benign liver lesions. Magnetic resonance (MR) is rapidly emerging as the imaging modality of choice for detection and characterization of liver lesions due to the high specificity resulting from optimal lesion-to-liver contrast and no radiation exposure. Improvements in breath-hold T1-weighted fast spoiled gradient echo and rapid T2-weighted single shot echo-train acquisition enable imaging of the liver in a single breath-hold with high spatial resolution. Most metastases are hypo- to isointense on T1 and iso- to hyperintense on T2-weighted images. MR contrast agents provide critical tumor characterization and can be safely used in patients with iodine contrast allergy and renal failure. Other agents, including newly developing gadolinium-chelates or iron oxide agents may provide additional benefits in selected applications. The degree and nature of tumor vascularity form the basis for liver lesion characterization based on enhancement properties. Liver metastases may be hypovascular or hypervascular. Colon, lung, breast and gastric carcinomas are the most common tumors causing hypovascular liver metastases, and typically show perilesional enhancement. Neuroendocrine tumors including carcinoid and islet cell tumors, renal cell carcinoma, breast, melanoma, and thyroid carcinoma are tumors most commonly causing hypervascular hepatic metastases, which may develop early enhancement with variable degrees of washout and peripheral rim enhancement.

Figure 1

Melanoma metastasis in liver. Lesion demonstrates heterogenous areas of elevated signal (arrow) on the T1W gradient echo image, characteristic of melanin-containing tumors such as melanoma.

Figure 2

Islet cell tumor metastases. (a) T2W image demonstrates a well-circumscribed large mass replacing the right lobe of the liver. The central (arrow) hyperintense area represents necrosis as the metastases has rapidly outgrown its blood supply. Post-contrast T1W images reveal heterogenous enhancement of the peripheral viable portion of the metastases in arterial phase (arrow in (b)). In portal venous (c) and delayed phase (d), the lesion is iso- to hypo-intense to the liver, with the central necrotic portion (arrow) remaining unenhanced. Another small metastatic lesion (arrowhead) is seen in the left lobe of the liver.

Figure 3

Hypervascular liver metastasis from breast carcinoma: (a) The lesion (arrow) is hypointense on the T1W image and (b) iso- to hyperintense (arrow) on the T2W image. (c) Arterial phase gadolinium-enhanced T1W gradient echo image shows enhancement of the lesion (arrow). The lesion becomes iso-intense to the liver in the portal venous phase (d).

Figure 4

Colon carcinoma metastasis. (a) T1W image shows a well-circumscribed hypo-intense mass (arrow) in the right lobe of the liver. (b) In post-contrast arterial phase T1W image, the mass remains hypo-intense with a subtle continuous rim of perilesional enhancement (arrow). (c) Portal venous phase images show heterogenous peripheral enhancement (arrow) with no enhancement of the center due to necrosis.

Figure 4

Colon carcinoma metastasis. (a) T1W image shows a well-circumscribed hypo-intense mass (arrow) in the right lobe of the liver. (b) In post-contrast arterial phase T1W image, the mass remains hypo-intense with a subtle continuous rim of perilesional enhancement (arrow). (c) Portal venous phase images show heterogenous peripheral enhancement (arrow) with no enhancement of the center due to necrosis.

Figure 5

Hypovascular liver metastases from pancreatic adenocarcinoma. (a) T1W image shows hypo-intense lesion (arrow) in segment VII of the liver, which is hyper-intense (arrow) on the T2W image (b). (c) Lesion demonstrates subtle concentric perilesional enhancement (arrow) on post-contrast arterial phase image. (d) On portal venous phase image perilesional enhancement becomes iso-intense to background liver and the center of the lesion (arrow) does not enhance due to necrosis.

Figure 6

Cystic liver metastasis from papillary cystic ovarian tumor. (a) Post-contrast T1W image in portal venous phase shows a hypo-intense non-enhancing lesion in segment VI of the liver, which is homogenously hyper-intense on T2W image (b). (c) Post-contrast T1W image of the pelvis shows a lobulated multi-septate cystic mass (arrow) with thin peripheral rim enhancement (double arrows). This cystic mass is hyper-intense (arrow) on the T2W image (d).