Papillary thyroid carcinoma with metastasis to the frontal skull

Papillary thyroid carcinoma with metastasis to the frontal skull is extremely rare. We report a case of unsuspected papillary thyroid carcinoma with frontal skull metastasis. The patient was a 62-year-old African American woman with presentation of a 4-cm firm, painless, immobile, ill-defined mass at the right forehead. Ultrasound and computer tonography detected a hypervascular and osteolytic tumor involving the skull and overlying skin. Fine-needle aspiration was performed followed by surgical biopsy. Cytologic examination revealed the presence of hypercellular and bloody material. The neoplasm showed glandular features and was composed of clusters of round to oval cells with pinkish squamoid cytoplasm, oval nuclei and inconspicuous nucleoli on smears and sections of cell block. With immunocytochemical stain, the neoplastic cells were positive for pancytokeratin and vimentin and focally positive for EMA, while they were negative for S100, HMB45, Melan-A, CD34, GFAP, CD10, LCA, RCC and CD138. The diagnosis was a metastatic carcinoma. Clinical follow up with surgical biopsy was recommended. Surgical biopsy demonstrated histological and cytological features of papillary thyroid carcinoma including prominent papillae, nuclear overlapping, grooves, and intranuclear pseudoinclusions. Thus, a diagnosis of metastatic papillary thyroid carcinoma was rendered. Though skull metastasis of thyroid carcinoma is rare, it should be considered in the differential diagnosis when a skull mass lesion is encountered.