A diagnostic pitfall: nodular tumor-like squamous metaplasia with Hashimoto's thyroiditis mimicking a sclerosing mucoepidermoid carcinoma with eosinophilia.

Nodular tumor-like squamous metaplasia with Hashimoto's thyroiditis is an exceptional, benign condition presenting diagnostic difficulties for the pathologist. The main differential diagnosis is a sclerosing mucoepidermoid carcinoma (SMC) with eosinophilia. One case arising in a 50-year-old Caucasian man is reported. Histologically, the nodule consisted of large nests of squamous cells surrounded by connective tissue in Hashimoto's thyroiditis. We present the different histological criteria, allowing us to eliminate an SMC and other neoplastic tumors of the thyroid. The etiology of this tumor-like lesion, which is still under debate, is discussed.