Endocrine Abstracts

Introduction: Riedel’s thyroiditis, also known as invasive fibrous thyroiditis, is a rare disorder of unknown etiology in which characterized by invasive fibrosis that partially destroys the thyroid gland and extends into adjacent neck structures. The diagnosis of Riedel’s thyroiditis is clinically difficult because this form of thyroiditis can mimic lymphoma or Hashimoto’s thyroiditis during preoperative radiologic, and pathologic examination. Sonographic features resemble thyroiditis with adjacent soft tissue extension.

Case report: A 60-year-old woman admitted to our institution with neck swelling without pain, dysphagia, dyspnea, and a recent history of hoarseness. On physical examination, there was a diffuse firm painless swelling in the anterior neck. Her serum free thyroxine, free triiodothyronine, and TSH levels are 1.40 ng/dl, 2.52 pg/ml, and 1.88 μIU/ml, thyroglobulin of 0.1 ng/ml (1.6–59.9 ng/ml), anti-thyroglobulin Ab of >1000 IU/ml (0–4.11 IU/ml), and anti-thyroid peroxidase Ab 405.7 IU/ml (0–5.61 IU/ml). Ultrasonography, computed tomography, and magnetic resonance imaging (MRI) of the neck revealed. All showed a diffusely enlarged mass covering both thyroid lobes, extending to the infra-hyoid level and encircling thyroid cartilage. This mass caused tracheal stenosis, but there was no evidence of tracheal invasion on MRI. Fine needle aspiration cytology revealed suspicious for lymphoma. Open-neck surgery was performed. surgical resection of the thyroid gland was successful but resection of soft tissue invasion was unsuccessful because the soft tissue invasion was markedly fibrotic. The final pathological diagnosis was Riedel’s thyroiditis. Histologically, the tumor showed extensive replacement of the thyroid parenchyma with dense keloidal fibrosis, intermixed well-developed lymphoid follicles, scattered lymphocytes, and plasma cells. After surgery l-thyroxine replacement therapy was started.

Conclusion: Ultrasonografic features of Riedel’s thyroiditis similar to malign thyroid lesions and frequently misdiagnosed as lymphoma on fine-needle aspiration cytology. Diagnostic thyroidectomy should be performed for the accurate diagnosis and treatment for Riedel’s thyroiditis.