Riedel's Thyroiditis Containing Cytologically Atypically Appearing B-cells: A Case Report

We report on a case of Riedel's thyroiditis containing cytologically atypically appearing B-cells. The patient was a 60-year-old Japanese female, who had a well-demarcated tumor that showed extensive growth from the right thyroid lobe into perithyroidal soft tissues. Histologically, the lesion consisted of two components. The central tumor-like portion of the mass showed spindle cells intermixed with abundant collagen fibers. In addition, scattered B-cells with large nuclei and multiple small, but conspicuous nucleoli were also present. At the periphery of the nodule, numerous plasma cells and small lymphocytes, as well as occasional B-immunoblasts and plasmablasts were growing between non-neoplastic thyroid follicles. An infiltration of thyroid follicles by B-cells also resulted in lymphoepithelial-like lesions. The specimen obtained from an enlarged cervical lymph node occurring 14 months later contained numerous mature plasma cells showing a sheet-like arrangement with occasional immature plasma cells and immunoblasts in the interfollicular area and medullary cords. The polyclonal nature of B-cells was demonstrated immunohistochemically and by polymerase chain reaction in both the thyroid gland and the lymph node lesion.