Extreme squamous metaplasia in Hashimoto's thyroiditis

The derivation of metaplastic squamous epithelium of the thyroid gland has been the subject of a number of embryologic studies. Small foci of benign squamous epithelium may be seen as an incidental finding in surgical specimens. Rarely an entire lobe, simultaneously affected by chronic lymphocytic thyroiditis, may be diffusely infiltrated by metaplastic epithelium. This borderline squamous cell metaplasia of the human thyroid gland must be distinguished from malignancy.