Thyroid-like Follicular Carcinoma of the Kidney
Variably sized follicles with colloid-like material are seen. The microfollicles on the left have small abortive lumens imparting a solid appearance. The differential diagnosis includes metastatic thyroid carcinoma to the kidney. The presence of a confirmed thyroid primary, nuclear features of papillary thyroid carcinoma, metastases to other locations besides kidney, and finally, immunoreactivity for TTF-1 and/or thyroglobulin would favor metastases over a primary renal neoplasm.