Thyroiditis: clinical aspects and diagnostic imaging.

Thyroiditis belongs to a heterogeneous group of inflammatory thyroid diseases. Hashimoto's thyroiditis, has an autoimmune pathogenesis: patients can be euthyroid or develop hypothyroidism, but may also experience transient thyrotoxicosis. Silent and postpartum thyroiditis also recognize an autoimmune origin; their clinical course being characterized by transient thyrotoxicosis occurring either sporadically or post-partum. Subacute thyroiditis is a painful, inflammatory disease of viral origin. Acute thyroiditis is a rare, serious, bacterial inflammatory disease. Riedel's thyroiditis is a rare chronic inflammatory disorder of unknown etiology, characterized by dense thyroid fibrosis. A diffuse thyroid hypoechogenicity is the hallmark of Hashimoto's thyroiditis, due to extensive lymphocytic infiltration of the gland. In postpartum and silent thyroiditis a diffuse or multifocal hypoechogenicity is found, while subacute thyroiditis is characterized by multiple ill-defined and migrating hypoechogenic areas. Both in acute and Riedel's thyroiditis there is marked hypoechogenicity.