Fig 1.
Cytologic features of histologically proven follicular adenoma and carcinoma, and Hurthle cell adenoma and carcinoma.
(A) A representative case classified as diagnostic category (DC) III (atypia of undetermined significance) showing sparsely cellular specimen (x15; scale bar, 200 μm). (B) A case diagnosed as DC IV (suspicious for a follicular neoplasm) shows moderately cellular specimen with abundant microfollicles (x15; scale bar, 200 μm) (C-F) Architectural alterations such as microfollicles (C and D), 3-dimensional branching (E), and architectural crowding (F) are frequently observed in cases categorized as DC IV (suspicious for a follicular neoplasm). In some cases, thick colloid (D) is noted within microfollicles (arrows) (x200; scale bar, 50 μm).
Fig 2.
Cytologic features of histologically proven Hurthle cell adenoma and carcinoma.
(A) Transgressing vessels are common in both Hurthle cell adenoma and carcinoma (x100; scale bar, 100 μmμ). (B) Cells generally show hyperchromatic nuclei with abundant granular cytoplasm (x200; scale bar, 50 μm). (C-F) Small cell dysplasia (C), large cell dysplasia (D), and prominent nucleoli (E) are seen in some cases. Importantly, focal chromatin clearing and nuclear groove (F) could be observed, features of which, can lead to misdiagnosis (x400; scale bar, 20 μm).
Fig 3.
Representative images of microfollicles arranged in trabecular pattern.
(A-C) Microfollicles arranged in trabecular (A and B) or branching patterns (C) are predominantly observed in follicular thyroid carcinoma (x200; scale bar, 50 μm).
Table 1.
Original thyroid FNAC diagnostic categories of histologically proven follicular adenoma and carcinoma, and Hurthle cell adenoma and carcinoma.
Table 2.
Revised thyroid FNAC diagnostic categories of histologically proven follicular adenoma and carcinoma, and Hurthle cell adenoma and carcinoma.
Fig 4.
Representative cytologic and histologic features of misdiagnosed cases.
(A-C) Case No. 50. (A) Nuclear atypia including chromatin clearing and nuclear groove (arrows) is present focally. (B) Microfollicles are focally noted. (C) Histologic features are consistent with follicular adenoma. (D-F) Case No.103. (D and E) Mild chromatin clearing and focal nuclear grooves are present. (F) Resected specimen reveals Hurthel cell carcinoma. (G-I) Case No. 27. (G) Artifacts mimicking intranuclear pseudoinclusion are noted. (H) However, the sample is entirely composed of Hurthle cells, and unequivocal nuclear atypia is absent. (I) Resection specimen reveals Hurthle cell carcinoma. (A, B, D, E, G, H; x400; scale bar, 20 μm) (C, F, I; x200; scale bar, 50 μm).
Table 3.
Summary of the thyroid FNACs with revised diagnosis upon review.
Fig 5.
Comparison of Diagnostic Categories (DCs) of Fine Needle Aspiration Cytology (FNAC) and Core Needle Biopsy (CNB).
(A) Among the 66 cases with both FNAC and CNB DCs available, 8 (53.3%), 1 (33.3%), and 22 (46.8%) cases with non-diagnostic, benign, and atypia of undetermined significance (AUS) DCs in original FNAC diagnoses were re-categorized as DC IV (suspicious for a follicular neoplasm) in CNB. (B) 8 (50.0%), 1 (50.0%), and 17 (41.5%) cases classified as non-diagnostic, benign, and AUS with the revised FNAC diagnoses were diagnosed as DC IV (suspicious for a follicular neoplasm) in CNB, suggesting under-diagnosis in FNAC.
Table 4.
Thyroid CNB diagnostic category of histologically proven follicular adenoma and carcinoma, and Hurthle cell adenoma and carcinoma.
Table 5.
Comparison of cytological features according to FNAC diagnostic category.
Table 6.
Comparison of histologic features of tumor in resection specimen according to FNAC diagnostic category.
Table 7.
Comparison of cytological features between histologically proven benign and malignant neoplasms.