Colorectal liver metastasis is the most common secondary liver malignancy. Up to 50% of colorectal cancers develop liver metastases, approximately half of which are present at diagnosis (synchronous). Due to portal venous drainage, the liver is the most common site of colorectal cancer metastasis. Typically presents as multiple hypovascular lesions. Characteristic target sign (rim enhancement) on CT, diffusion restriction and hepatobiliary phase hypointensity on MRI are diagnostic clues. Post-treatment calcification may be seen. Surgical resection of resectable metastases offers up to 50% 5-year survival.
Age Range
40-80
Peak Age
65
Gender
Equal
Prevalence
Very Common
Colorectal cancer cells reach the liver via the portal venous system. Tumor cells adhere to sinusoidal endothelium and invade the parenchyma, growing through neovascularization. Colorectal metastases are typically hypovascular because the tumor stroma shows desmoplastic reaction and neovascularization is fed by the hepatic artery. Rim enhancement reflects arterial supply to active tumor tissue at the lesion periphery, while central hypodensity represents necrosis or mucinous content. HBP hypointensity results from the inability of metastatic tissue to take up gadoxetic acid due to absence of hepatocytes.
On hepatobiliary phase: hypointense metastasis core + perilesional bright hepatocyte ring — compensatory gadoxetic acid uptake by compressed hepatocytes. Highly specific for colorectal metastasis and valuable in differential diagnosis from other hypovascular lesions.
Thin rim enhancement at the lesion periphery in arterial phase (target pattern). Center remains hypodense. In hypovascular metastases, the lesion may not be conspicuous in arterial phase.
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Lesion demonstrating peripheral rim enhancement in arterial phase, consistent with colorectal metastasis.
Distinctly hypodense lesion compared to liver parenchyma on portal venous phase. This is the most sensitive CT phase for detecting colorectal metastases because normal parenchyma enhances maximally while metastasis remains hypodense.
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Hypodense lesion(s) relative to liver parenchyma on portal venous phase.
Marked hyperintensity on DWI with low signal on ADC map — diffusion restriction. Most sensitive MR sequence for detecting small metastases (<10 mm). Optimal contrast achieved at b=800-1000 values.
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Lesion(s) demonstrating diffusion restriction on DWI, consistent with high cellularity.
Distinctly hypointense lesion on hepatobiliary phase (20 min after gadoxetic acid). Perilesional hepatocyte ring (target sign) is pathognomonic — inner portion dark (metastasis), outer ring bright (compressed hepatocytes retain more gadoxetic acid). Highest sensitivity for small metastases combined with DWI.
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Hypointense lesion(s) with perilesional hepatocyte ring (target sign) on hepatobiliary phase, highly consistent with colorectal metastasis.
Moderate hyperintensity on T2-weighted images. Perilesional hyperintense halo may be seen due to edema or mucinous content. Distinguished from marked T2 hyperintensity of hemangioma ('light bulb sign') by lower signal intensity.
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Moderate hyperintense lesion with perilesional halo on T2-weighted images.
Target/bull's-eye pattern on US: hypoechoic peripheral ring + echogenic center. Small metastases (<2 cm) may be homogeneously hypoechoic or hyperechoic. Multiple lesions in colorectal cancer context are highly suspicious.
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Lesion(s) demonstrating target/bull's-eye pattern on US, consistent with metastasis.
Thin peripheral rim enhancement on MRI arterial phase. Similar to CT rim enhancement but better defined due to MRI's soft tissue contrast. With gadoxetic acid, contrast behaves like extracellular contrast in early phases.
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Peripheral rim enhancement on MRI arterial phase, consistent with hypovascular metastasis.
Criteria
Most common type (80-90%). Rim enhancement, hypodense on portal venous phase, DWI positive. Desmoplastic stroma predominant.
Distinct Features
Distinct hypodensity on portal venous phase, rim enhancement, HBP target sign
Criteria
Originating from mucinous adenocarcinoma (10-15%). Very high T2 signal (mucin content), low CT density, cyst-like appearance.
Distinct Features
Very high T2 signal (may mimic hemangioma), low CT density, minimal enhancement, peripheral restriction on DWI
Criteria
Post-chemotherapy size reduction, calcification development, decreased enhancement. 'Vanishing metastasis' phenomenon — lesions appearing to disappear on CT but containing 20-80% viable tumor on pathology.
Distinct Features
Calcification, size reduction, decreased DWI signal — but caution needed in complete response assessment
Distinguishing Feature
ICC is usually solitary, shows centripetal delayed fill-in, causes capsular retraction and biliary dilatation. Colorectal metastasis is typically multiple with rim enhancement + HBP target sign.
Distinguishing Feature
Hemangioma shows very high T2 signal ('light bulb sign'), peripheral nodular enhancement and centripetal fill-in. Colorectal metastasis shows moderate T2 hyperintensity, rim enhancement and DWI restriction.
Distinguishing Feature
Pyogenic abscess is distinguished by clinical features (fever, leukocytosis), double ring sign, perilesional edema and transient hepatic attenuation difference (THAD). Abscess shows very high DWI signal but clinical context differs.
Distinguishing Feature
Neuroendocrine metastases are hypervascular — show marked homogeneous enhancement in arterial phase. Colorectal metastasis is hypovascular with rim enhancement. Primary tumor location and clinical markers (chromogranin A) are distinguishing.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
3-monthSurgical resection of resectable liver metastases has curative potential (40-50% 5-year survival). Neoadjuvant chemotherapy (FOLFOX/FOLFIRI ± biologic agent) enables downsizing. Accurate determination of number and location is critical for surgical planning — DWI + HBP combination has highest sensitivity. Biopsy is usually unnecessary; known colorectal cancer + typical imaging findings suffice for diagnosis. Follow-up CT/MRI at 3-month intervals is recommended.
Surgical resection of resectable liver metastases offers up to 50% 5-year survival. Neoadjuvant chemotherapy (FOLFOX/FOLFIRI) enables downsizing. DWI and HBP are the most sensitive methods for detecting small metastases. Accurate determination of number and location prior to surgery is critical.