Riedel thyroiditis is a rare, chronic inflammatory disease of the thyroid gland characterized by dense fibrosis that replaces normal thyroid parenchyma and extends beyond the thyroid capsule to adjacent structures of the neck. The cause of Riedel thyroiditis is unknown but is thought to be either an autoimmune or IgG4-mediated systemic fibrotic process. Thyroid function is variable, with most patients being euthyroid. Thirty percent of patients are hypothyroid at the time of presentation.

Most patients typically present with a nonpainful, rapidly growing thyroid mass often associated with airway obstruction, dysphonia, hoarseness, hypoparathyroidism, dysphagia, or stridor.

Physical examination reveals a large goiter with a hard or woody texture. At the time of presentation, approximately one-third of patients present with extracervical manifestations of multifocal fibrosis, including retroperitoneal, mediastinal, pulmonary, or lacrimal gland fibrosis; orbital pseudotumor; sclerosing cholangitis; or fibrosing parotitis.