C. Acute tubular necrosis secondary to kidney melanoma metastasis
The kidney is an uncommon site of clinically apparent melanoma metastases. While kidney micrometastases may be found in up to half of patients with a history of melanoma on postmortem evaluation, they are typically subclinical small cortical nodules.2,3 The few cases of symptomatic kidney involvement from melanoma have been secondary to large cortical masses that can be visualized on imaging.4- 7 Thus, symptomatic kidney micrometastases and/or isolated tumor cells with intracapillary involvement are a rare phenomenon.
The patient’s biopsy findings were suggestive of acute tubular necrosis (ATN) that followed metastatic melanoma cells occluding kidney capillaries and limiting blood flow to tubules. The specimen stained with hematoxylin and eosin showed intracapillary atypical cells with enlarged nuclei, prominent nucleoli, and abundant cytoplasm (Figure, A) and diffuse mild acute tubular injury with tubular dilatation and extensive isometric cytoplasmic vacuolization of tubular epithelial cells (Figure, B), which were consistent with ATN. Intracapillary atypical cells were positive for melanin-A (Figure, C), Sry-related HMg-Box gene 10, S-100, and human melanoma black–45 stains, which indicated the presence of melanoma micrometasases. These findings may account for the abnormal intraparenchymal flow that was visualized on ultrasonography, although no positron emission tomography avidity was appreciated in the kidneys.