Morphologic and planimetric diagnosis of follicular thyroid lesions on fine needle aspiration cytology.

During 1989-1992, 2,729 fine needle aspiration biopsies were performed; 585 with histologic controls were reviewed. The aim of the study was to demonstrate the incidence of carcinoma in follicular-structured smears without nuclear enlargement, evaluated with planimetric techniques, and to suggest a new cytodiagnostic classification. Of 398 follicular-structured smears, 188 were colloid nodules, 38 were thyreocytic hyperplasias without nuclear atypia, 146 were predominantly follicular lesions (PFL) and 26 were follicular lesions with nuclear pleomorphism. The last showed a high incidence of neoplasia (69.2%) and carcinoma (46.1%) and the largest planimetric values for nuclear area, perimeter and maximum diameter. The second and third categories showed only a difference in the incidence of benign neoplasms (32.9 vs. 15.8%). These results suggest that six months of expectant management might be useful in simple follicular lesions, whereas a follicular pattern with nuclear enlargement requires surgical treatment for the strong possibility of carcinoma.