Metastatic thyroid carcinoma mimicking as a primary neoplasia of the kidney: A case report

The unfavorable behavior of primary thyroid carcinoma (PTC) has been revealed by the hematogenous distant metastases in ~20-25% of cases with frequent localizations in lungs and bones, but infrequently in kidney. A 69-year-old male patient was admitted to Department of Human Pathology in Adulthood and Childhood ‘G. Barresi’, University Hospital G. Martino, (Messina, Italy) for an incidentally detected parenchymal mass involving the right kidney. A partial nephrectomy was done; at the post-surgical examination, a large nodular grayish mass was documented. Microscopically, a diffuse proliferation with solid/follicular pattern with some colloid-filled spaces was appreciable. An intense immunopositivity was revealed for thyroglobulin, thyroid transcription factor-1 (TTF-1), paired-box gene 8 (PAX-8) and cytokeratin 7, while CD10 and renal cell carcinoma marker were negative. A diagnosis of the metastatic thyroid follicular carcinoma localized in the kidney was made. At ultrasound examination, a hyperechoic mass extending from the left thyroid lobe to the isthmus, to which TIR4 diagnostic category according to the Italian reporting system for thyroid cytology was attributed. After thyroid surgical procedure, the final diagnosis of primitive differentiated follicular thyroid carcinoma with foci of poorly differentiated component was made.