Riedel’s thyroiditis: rare disorder that typically occurs in middle-aged women; AI; presents with an insidious, painless goiter with local symptoms due to compression of the esophagus, trachea, neck veins, or recurrent laryngeal nerves. Dense fibrosis disrupts normal gland architecture and can extend outside the thyroid capsule. Despite these extensive histologic changes, thyroid dysfunction uncommon. goiter is hard, nontender, often asymmetric, and fixed, leading to suspicion of a malignancy; Diagnosis: open biopsy; Treatment: surgical relief of compressive symptoms. Tamoxifen may also be beneficial. There is an association between Riedel’s thyroiditis and IgG4-related systemic disease causing idiopathic fibrosis at other sites (retroperitoneum, mediastinum, biliary tree, lung, and orbit).