Riedel’s Thyroiditis Occurring in a Multinodular Goiter, Mimicking Thyroid Cancer

Abstract

A 52-yr-old female with multinodular goiter with benign fine-needle aspiration (FNA) cytology presented with progressive compressive symptoms. Clinically, the left lobe was enlarged, painless, but firm. Serum TSH and calcitonin were normal, and thyroglobulin was elevated. C-reactive protein and leukocyte counts were normal. Thyroid-related autoantibodies (thyroid peroxidase, thyroglobulin, and TSH receptor) were absent. The ultrasound performed 1 yr before showed hyperechoic nodules (Fig. 1A). Now, the volume of the left lobe increased nearly 2-fold due to hypoechoic, hypovascular tissue surrounding the hyperechoic nodules (Fig. 1B). During FNA, the hypoechoic tissue felt remarkably harder than the hyperechoic nodules. Cytology of the nodules was confirmed to be benign. However, cytology of the hypoechoic part showed a small amount of follicular epithelial cells with enlarged, irregular nuclei and no colloid. Based on the inconclusive cytology, the absence of biochemical abnormalities, and the increasing mechanical complaints, a total thyroidectomy was performed. During surgery, a white stony-hard left thyroid lobe was disclosed. Histopathologic examination showed a sclerotic mass, consisting of spindle-shaped cells and mononuclear inflammatory cells, infiltrating the follicular adenomas (Fig. 2), leading to the diagnosis of Riedel’s thyroiditis. This is a rare fibrosclerotic infiltrative thyroid disorder of unclear etiology, during which normal thyroid tissue is replaced by fibrous tissue, hypoechoic and hypovascular on ultrasound (2, 3), often expanding outside the thyroid capsule, and sometimes part of multifocal (retroperitoneal, retroorbital, and mediastinal) fibrosclerosis (1–3). The main differential diagnosis is invasive thyroid cancer. FNA often fails to distinguish between these two entities, and the diagnosis can be complicated further in an already nodular thyroid.