Urogenital Imaging

Metastasis, renal

A variety of primary neoplasms may metastasize to the kidney including carcinoma of the breast, stomach, colon and lung, and lymphoma, melanoma and leukaemia. Metastases to the kidneys are often small, clinically silent and detected only at autopsy. Renal metastases may present as multiple small renal masses or, less commonly, as a solitary lesion. Solitary renal metastases cannot be distinguished from primary renal cell carcinomas on the basis of imaging characteristics. Metastatic renal lesions usually do not distort the renal contour, but may have a variable appearance (Fig.1).

Renal involvement of lymphoma is variable in appearance and often associated with retroperitoneal lymphadenopathy. Diffuse infiltration of the kidneys may produce global renal enlargement. Lymphoma may present as a focal solitary or multiple intrarenal masses which may be unilateral or bilateral. Subcapsular and perirenal lymphomatous infiltration may be seen. On CT, renal lymphoma appears as a homogeneous mass with enhancement lower than adjacent renal parenchyma. On MRI, renal lymphoma is typically iso- to slightly hypointense to renal cortex on T1-weighted images and is hypointense to renal cortex on T2-weighted images. No significant enhancement is seen on dynamic breathhold GRE images or post-contrast T1-weighted images. Leukaemic infiltration of the kidneys usually produces bilateral renal enlargement with loss of the corticomedullary junction on T1-weighted images and may appear similar to renal lymphoma.

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Fig.1

Axial contrast-enhanced CT section through the kidneys, showing a metastasis (arrow) from a cutaneous melanoma in the right kidney.
Metastasis, renal, Fig.1