Follicular Growth Pattern Disease on Thyroid Fine-needle Aspiration Biopsy

Abstract

Thyroid nodules are a common worldwide health problem and a diagnostic challenge for clinicians and cytopathologists. Follicular growth pattern constitutes the majority of thyroid lesions. Thyroid nodules can be neoplastic or non-neoplastic, and neoplastic nodules can be classified as benign, malignant, or gray zone. Gray zone lesions include different benign and malignant entities that might be resulted in unnecessary thyroidectomies with risk of morbidity and higher health care costs. Depending on the cellularity, most cases might fall into the follicular neoplasia (FN)/ suspicious for FN (SFN) category or follicular lesion of undetermined significance (FLUS) in The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC). Pathologists must be aware of the relationship between this diagnostic category and follow-up patient management and avoid over-diagnosing by mastering the diagnostic criteria.

Figure 1

Hyperplastic nodule on fine-needle aspiration biopsy. Benign follicle epithelial cells with few follicular structures (arrows) near colloidal material (PAP x200)

Figure 2

Follicular neoplasms (FN)/suspicious for FN (SFN) with numerous microfollicules (arrows) on fine-needle aspiration biopsy (PAP x400)

Figure 3

Follicular variant papillary thyroid carcinoma with few follicular structures on fine-needle aspiration biopsy (arrows: microfollicles, asterisk: intranuclear pseudo inclusion), (a. Giemsa x400, b. PAP x200)

Figure 4

Medullary carcinoma with few follicular structures (arrows) on fine-needle aspiration biopsy (PAP x400)