Answer: Negative for tumor

Histology: The thyroid is infiltrated by lymphocytes and plasma cells, with germinal centers. The thyroid follicular epithelium exhibits oncocytic (i.e. Hurthle cell) metaplasia. These findings are diagnostic for Hashimoto thyroiditis. At the cytologic level, there are areas of nuclear atypia including enlargement, clearing, overlapping, and grooves.

Discussion: Patients with Hashimoto thyroiditis are at increased risk for extranodal MALT lymphomas, and perhaps papillary thyroid carcinoma (this is controversial). A MALT lymphoma would appear as sheets of monocytoid cells with the lymphocytes spilling into and packing thyroid follicles; those findings are not present in this case. In addition, while papillary carcinoma is defined by its nuclear features, it is important to recognize that inflammatory conditions like Hashimoto thyroiditis can induce reactive epithelial changes that may overlap considerably with those of papillary cancer. These changes can be differentiated from carcinoma by recognizing their diffuse nature (i.e., not forming a discrete mass) with accentuation in areas of severe inflammation, lack of an infiltrative pattern or stromal fibrotic reaction, and the absence of more specific findings like papillary architecture or psammoma bodies.