[Riedel's thyroiditis: current aspects].

Riedel's thyroiditis is a rare form of chronic thyroiditis characterized by extensive fibrosis of the thyroid gland, also affecting adjacent tissue. Riedel's thyroiditis clinically resembles anaplastic thyroid or lymphoma, with a woody goiter attached to adjacent structures, and compressive. Findings from scintigraphy, ultrasonography, and cytology are rarely conclusive.