Papillary thyroid carcinoma and related thyroid neoplastic lesions: A light microscopic study with emphasis on nuclear changes

A total of 187 thyroid lesions consisting of 2 cases of Grave's disease, 21 cases of multinodular goiter, 40 follicular adenomas and 124 low-grade pap illary thyroid carcinomas were studied to identify intermediate neoplastic lesions in the spectrum of nuclear changes between benign reactive thyroid follicles and low-grade thyroid papillary carcinoma. The lesions were exami ned and classified on the basis of the following nuclear features: fine chr omatin seen in the thyroid papillary carcinomas and coarse chromatin seen i n follicular carcinomas. Cases with Hurthle cell changes were excluded from the study. Cases with nuclei containing coarse chromatin were classified i n the group of follicular adenomas with a coarse chromatin pattern. The neo plastic thyroid lesions containing fine chromatin showed a spectrum of nucl ear changes ranging between reactive follicular lesions and papillary thyro id carcinoma with lymph node metastasis. Such lesions were classified as fo llicular adenomas with a fine chromatin pattern. The nuclei of these lesion s were graded into mild to marked "nuclear atypia with a fine chromatin pat tern". The degree of atypia depended on the degree and extent of nuclear ch anges. Encapsulated follicular adenomas with a fine chromatin pattern and w ith mild atypia (11 cases), moderate atypia (13 cases), marked atypia (27 c ases), and encapsulated or nonencapsulated papillary thyroid carcinoma were characterized by uniform nuclei; with mild, moderate and marked nuclear at ypia in less than 2/3 of the cell population and marked nuclear atypia in m ore than 2/3 of the cell population; and measuring 5.4-6.3, 6.0-7.2, 6.3-9 and 7.2-10 microns in diameter, respectively, Follow-up of cases of papilla ry thyroid carcinoma fulfilling the above criteria showed lymph node metast asis in 33% of cases, whereas follicular adenomas with a fine chromatin pat tern, including cases originally diagnosed as papillary carcinoma, showed n o evidence of lymph node or distant metastasis in a follow-up period of 30 months to 15 years. In the thyroid tissue surrounding papillary thyroid car cinoma or encapsulated follicular adenoma with a fine chromatin pattern and marked atypla, adenomatous nodules with a fine chromatin pattern and with low-grade nuclear atypia were identified. The adenomatous nodules with a fi ne chromatin pattern and with mild, moderate and marked atypia showed archi tectural, cytoplasmic and nuclear features similar to those of follicular a denoma with a fine chromatin pattern of the same grade. Of interest, a larg e number of cases of follicular adenoma with a fine chromatin pattern had a reas with features of follicular adenoma with a coarse chromatin pattern.