Metastases to the kidney: a clinicopathological study of 43 cases with an emphasis on deceptive features

To review our experience with metastases to the kidney in surgical pathology material.

The clinicopathological features of all metastases to the kidney in surgical pathology cases between May 1987 and May 2013 at our institution were reviewed. Autopsy cases were excluded. Forty-three cases (16 nephrectomies, 25 biopsies, and two fine needle aspirations) were included; the primary malignancy was diagnosed prior to/concurrently with the metastasis in nearly all cases. Common primary sites included the lung, breast, female genital tract, and head and neck; the majority were carcinomas. A primary renal tumour was suspected prior to the pathological diagnosis in 35% of cases. Unusual features included: common unilateral (77%) and unifocal (70%) involvement, lack of other distant organ metastases (37%), >10 years between primary and metastasis diagnoses (19%), lack of a discrete mass (5%), and renal vein extension (19% of resections). The most common dilemma was excluding urothelial or high-grade renal cell carcinoma; however, metastases from the thyroid commonly mimicked low-grade renal cell carcinomas.

In surgical pathology material, metastases to the kidney most commonly present as solitary unilateral masses, and in a substantial subset of cases mimic a primary renal tumour.