Multiple intraglandular foci are frequent, especially in children. Areas of lymphocyte infiltration, and even extensive lymphocytic thyroiditis, are common, especially in papillary tumors. Many tumors look much like follicular cancers, but have the characteristic nuclei of papillary cancers. Fig ure 18-9. Papillary carcinoma of the thyroid.
Little colloid is visible.
Such histologic foci may be encapsulated, sclerosing, invasive, or multicentric. Follicular variant of papillary carcinoma with crowded nuclei showing nuclear folding and peripherally vacuolated colloid. Follicular adenocarcinomas vary from those with a definite follicular pattern to those with solid sheets of cells. The lesions are more frequently encapsulated, but capsular and blood vessel invasions are typical. The nuclei are normo- or hyper chromated, or may be quite vesicular.