Riedel's thyroiditis and fibrous variant of Hashimoto's thyroiditis: a clinicopathological and immunohistochemical study.

The aim of this study was to analyze and compare clinico pathological aspects of Riedel's thyroiditis (RT) and the fibrous variant of Hashimoto's thyroiditis (HTFV), and to show their immunohistochemical features. We reviewed 6 cases of HTFV and 4 cases of RT. Compared to RT, HTFV patients had hypothyroidism, no pressure symptoms, and frequently diagnostic fine-needle aspiration biopsy (FNAB) cytology. At histology, invasion of surrounding tissues and presence of occlusive phlebitis distinguished RT from HTFV. At immunohistochemistry, RT--compared to HTVF--was characterized by: 1) a more abundant fibrous reaction, and granulocytic, monocytic and eosinophil infiltration; 2) few plasma-cells, CD8+ T- and B-lymphocytes. The results of our study add further evidence regarding the separation of RT and HTFV in their peculiar clinical, laboratory, cyto-histological and immunohistochemical aspects.