KEY FACTS
Imaging
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Usually small and round, may be wedge-shaped
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Usually cortical; rarely disrupting renal contour or capsule
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Large, exophytic metastases may be encountered
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Hypoechoic, hyperechoic, or sonographically occult
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Occasionally infiltrative
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Perinephric infiltration from tumor extension or hemorrhage may be seen (melanoma)
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Mostly avascular or hypovascular using low-flow Doppler settings
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Melanoma (and other hypervascular primary tumors) metastasis can be hypervascular, simulating renal carcinoma
Top Differential Diagnoses
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Primary renal malignancy
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Renal angiomyolipoma
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Renal cysts (complex)
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Renal lymphoma or leukemia
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Renal infection
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Renal infarction
Clinical Issues
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May have hematuria or microhematuria (12-31%)
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Most are clinically occult and found on imaging or at autopsy
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Most common malignant renal tumor at autopsy (7-13% of autopsies); 20% of patients dying of disseminated malignancy
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Most patients have metastatic tumor at other locations
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Lung cancer most common primary site followed by breast, gastric cancer, melanoma, and lymphoma
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Prognosis very poor
Scanning Tips
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Metastases may be subtle on ultrasound; use color Doppler at low-flow settings
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Presence of disseminated malignancy suggests metastases as cause of abnormal renal ultrasound
representing metastatic melanoma. This cannot be distinguished from renal cell carcinoma.
. While the grayscale features are indistinguishable from renal cell carcinoma, metastases are typically hypovascular compared to renal cell carcinoma.
