Follicular Thyroid Carcinoma Metastatic to the Kidney: Report of a Case with Cytohistologic Correlation

Figure 2

Core biopsy imprints of the left renal mass showed an abundance of cells that resembled thyroid follicular cells arranged in large sheets (a) in a background containing proteinaceous material (Diff-Quik, 200x) (left). The cells possessed round to oval nuclei, uniformly distributed chromatin, and inconspicuous nucleoli, without any nuclear features of PTC such as longitudinal grooves, nuclear clearing, or intranuclear pseudoinclusions (Papanicolaou, 200x) (right). Histologic sections of the biopsy specimen showed variably sized colloid-filled follicles lined by flattened follicular cells, resembling normal thyroid (H&E, 200x) (b). The thyroid origin of the tumor was confirmed by immunohistochemical stains that demonstrated positive cytoplasmic expression of thyroglobulin (400x) (c) and positive nuclear expression of TTF-1 (400x) (d).

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