Fine-needle aspiration of follicular lesions of the thyroid. Diagnosis and follow-Up

Abstract

The differential diagnosis of a follicular lesion/neoplasm in thyroid FNA specimens includes hyperplastic/adenomatoid nodule, follicular adenoma and carcinoma, and follicular variant of papillary thyroid carcinoma. In our laboratory we separate follicular lesions of thyroid into hyperplastic/adenomatoid nodule (HN), follicular neoplasm (FON) and follicular derived neoplasm with focal nuclear features suspicious for papillary thyroid carcinoma (FDN). This study reports our experience with 339 cases diagnosed as FON and 120 as FDN. All cases were evaluated for histologic diagnosis, age, sex and size of the nodule. Histopathologic follow-up was available in all cases. The malignancy rate was 22% (74/359) and 72% (86/120) for cases diagnosed as FON and FDN, respectively. In the FON category almost half of the malignant cases were papillary carcinoma. The risk of malignancy was higher in patients younger than 40 yr (53% vs. 30%) than in patients 40 year or more years old and greater in males (41% vs. 33%) than females. No statistically significant relationship was noted between the sizes of the nodules and benign vs. malignant diagnosis. According to this study it is important to divide follicular patterned lesions of thyroid into FON and FDN in the cytology specimens due to significantly different risk of malignancy (22% vs. 72%). In addition, clinical features, including gender and age can be part of the decision analysis in selecting patients for surgery.

Figure 1

Monotonous population of follicular cells arranged in cohesive follicular groups with nuclear overlapping and crowding, case diagnosed as follicular neoplasm (1A). Histologic follow-up showing follicular adenoma (thickly encapsulated follicular patterned lesion with no capsular or vascular invasion), the inset shows the same nuclear features as seen in cytology (1B).

Figure 2

Diff-Quik^® stained smear demonstrating enlarged follicular cells in loosely cohesive groups (2A). Papanicolaou stained slides showing focal nuclear chromatin clearing and intranuclear grooves (arrows-Figs 2B-2C). Histologic follow-up showing follicular variant of papillary thyroid carcinoma, notice the nuclear features on high power (Figs 2D-2E).

Figure 3

Correlation between benign and malignant diagnoses, size of the thyroid nodule, age and sex of the patient.