Metastatic papillary thyroid carcinoma to the kidney: report of two cases mimicking primary renal cell carcinoma and review of the literature.

stalks. Calcified bodies are often seen in the stroma of papillomas. An atypical papilloma is defined by the presence of mitoses >2 per 10 high power fields (HPF) and two or more of increased cellularity, nuclear pleomorphism, solid growth and areas of necrosis. There are only two other reports of choroid plexus papillomata arising in mature cystic teratomas in the literature. In one report a choroid plexus papilloma developed in the wall of an ovarian dermoid in a 14-year-old female. In the other, an atypical choroid plexus papilloma with cytologic atypia, focal necrosis and mitoses up to 3/10HPF, was described arising in the wall of a dermoid in a 26-year-old female. Follow-up is limited in both cases. UsualWHO grade I choroid plexus papillomata arising in the central nervous system are considered benign and complete excision in these cases is considered curative. By extrapolation, the oophrectomies performed to remove the teratoma in the current case and the other reported cases are considered curative. Importantly, choroid plexus papillomata can be confused with other ovarian papillary epithelial neoplasms that may mimic primary or metastatic tumours including serous, clear cell or endometroid tumours, especially if associated with psammomatous calcifications. Metastasis from lung adenocarcinoma, papillary thyroid carcinoma, urothelial carcinoma and malignant mesothelioma would also enter the differential diagnosis. In conclusion, we describe another example of the rare phenomenon of a choroid plexus papilloma arising in a mature cystic teratoma of the ovary. Pathologists need to be aware of this entity so as not to confuse this with other well differentiated ovarian papillary epithelial neoplasms that may be primary or metastatic.