Riedel's Disease and Hashimoto's Thyroiditis 157 157 Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania Medical Center, Philadelphia, PA. Address correspondence to Dr. Zubair W. Baloch, Department of Pathology and Laboratory Medicine, 6 Founders Pavilion, Hospital of the University of Penn- sylvania Medical Center, 3400 Spruce Street, Philadel- phia, PA 19104. E-mail: baloch@mail.med.upenn.edu Endocrine Pathology, vol. 11, no. 2, 157–163, Summer 2000 © Copyright 2000 by Humana Press Inc. All rights of any nature whatsoever reserved. 1046–3976/00/11:157–163/ $11.75 Introduction Both benign and malignant lesions of the thyroid can be associated with extensive scle- rosis. Fibrosing Hashimoto’s thyroiditis and Riedel’s disease are among the benign lesions [1–9], whereas, in malignant lesions, papil- lary carcinoma and anaplastic carcinoma can exhibit acellular or paucicellular areas of hyalinization [10,11]. Fibrosing Hashimoto’s thyroiditis is seen in 10–13% of patients diagnosed as having lymphocytic thyroiditis [3,6–8,12]. It is characterized by effacement of the thyroid by fibrous bands with intermixed collec- Combined Riedel’s Disease and Fibrosing Hashimoto’s Thyroiditis: A Report of Three Cases with Two Showing Coexisting Papillary Carcinoma Zubair W. Baloch, MD, PHD, Michael D. Feldman, MD, PHD, and Virginia A. LiVolsi, MD Abstract Extensive sclerosis of the thyroid gland can be seen in both benign and malignant condi- tions. The benign sclerosing lesions of the thyroid include Riedel’s disease and fibrosing Hashimoto’s thyroiditis. Although these conditions usually occur separately, rarely can they occur simultaneously. In malignant lesions, papillary thyroid carcinoma and anaplas- tic carcinoma of the thyroid can be associated with extensive sclerosis leading to partial or total effacement of the tumor. We report on three cases that showed simultaneous occurrence of Riedel’s disease and fibrosing Hashimoto’s thyroiditis. Two of these cases also showed papillary carcinoma (one case of Warthin’s-like papillary carcinoma and one case of classic type). All patients were females (age range 32–67 yr) and presented with elevated antithyroglobulin antibodies. Two patients presented with a solitary thyroid mass, and from these one had multiple bilateral neck nodes and a paravertebral mass. The third patient presented with a multinodular gland adherent to neck structures. All patients underwent total thyroidectomy. Histologic sections showed extensive replace- ment of the thyroid parenchyma with dense keloidal fibrosis, intermixed well-developed lymphoid follicles, and scattered lymphocytes and plasma cells. In all cases the fibrotic process extended beyond thyroid capsule with involvement of the perithyroidal soft tis- sues and skeletal muscle consistent with Riedel’s disease. One case showed a classic pap- illary carcinoma with bilateral lymph node metastases, and the other showed a Warthin’s-like papillary carcinoma. In both cases the papillary cancers were surrounded by dense sclerosis. Immunohistochemical stains for B- and T-markers and immunoglobu- lin light chains showed a polyclonal population of the lymphoid cells. The simultaneous occurrence of Riedel’s disease and fibrosing Hashimoto’s thyroiditis is rare and most likely represents a coincidental phenomenon, because both of these conditions are distinct clinicopathologic entities. Key Words: Hashimoto’s thyroiditis; Riedel’s disease; thyroid sclerosis. Clinical Research