How do liver metastases appear on US CT and MRI?
US: Appearance is variable. Gastrointestinal and more vascular tumors (e.g., islet cell, carcinoid, choriocarcinoma, renal cell carcinomas) tend to produce hyperechoic metastases, which may mimic a hemangioma. Hypoechoic lesions are also common, particularly with lymphoma, breast, lung, and cystic or necrotic metastases. Hypoechoic halos surrounding liver masses produce the nonspecific but common “bull’s-eye” appearance often seen with malignant lesions; these require additional work-up.
MDCT: Most liver metastases have decreased attenuation compared with the surrounding parenchyma on NCCT. Most metastases are hypovascular (e.g., colon adenocarcinoma) and are best imaged in the PVP. Hypervascular metastases (i.e., renal cell, carcinoid, thyroid, melanoma, and neuroendocrine tumors) are best imaged during the HAP, which should be added to PVP imaging to increase lesion detection. Calcified metastases are most commonly seen with mucinous colon carcinoma.
MRI: In general, metastases are hypointense on T1-w and hyperintense on T2-w images. However, hemorrhagic and melanoma metastases are hyperintense on T1-w images. Dynamic gadolinium enhanced MRI increases the sensitivity for the detection of liver metastasis.