In papillary thyroid carcinoma (PTC) in cytological and surgical specimens,
fine chromatin, nuclear grooves and nuclear pseudoinclusions are the hallm
arks of diagnosis. We investigated the significance of these nuclear change
s in neoplastic non-PTC lesions. Fine needle aspiration biopsies (FNAB) of
thyroid lesions were reviewed with histologic correlation. Twenty-five low-
grade PTC and 35 neoplastic non-PTC lesions with a fine chromatin pattern i
n cytology specimens were identified. These lesions were studied along with
five multinodular goiters and five follicular adenomas with a coarse chrom
atin pattern. The neoplastic non-PTC lesions were selected from cases with
a histopathologic diagnosis of follicular neoplasm (accompanied by cytopath
ologic examination) but lacking a coarse chromatin pattern. The nuclear cha
nges were separated into three grades of nuclear atypia with a fine chromat
in pattern, depending on the degree of nuclear enlargement and nuclear memb
rane thickening, or the presence of nuclear grooves or pseudoinclusions. Th
yroid lesions with a higher grade of nuclear atypia with a fine chromatin p
attern were associated with larger nuclei and more readily visible nucleoli
. These lesions correlated histologically with PTC and follicular adenomas
with a fine chromatin pattern. The latter could be divided into three grade
s: grade 1 lesions having a fine chromatin pattern similar to that of nucle
i with open chromatin seen in areas of nodular goiter; grade 3 lesions havi
ng nuclear features closest to those of PTC; and grade 2 lesions showing in
termediate changes. In conclusion, there is a spectrum of nuclear changes i
n neoplastic non-PTC lesions with a fine chromatin pattern. These lesions a
re often diagnosed as follicular adenomas in surgical pathology and pose cy
topathologic diagnostic problems between nodular goiter, follicular adenoma
and PTC. The significance of follicular adenomas with a fine chromatin pat
tern will be discussed.