Abstract
Cytologic diagnosis of thyroid follicular adenoma and carcinoma, and Hurthle cell adenoma and carcinoma (FACHAC) is challenging due to cytomorphologic features that overlap with other follicular-patterned lesions. This study was designed to analyze diagnostic categories (DCs) of preoperative fine needle aspiration cytology (FNAC) of histologically proven thyroid FACHACs to evaluate under- or misdiagnoses in FNAC and elucidate potential causes for such phenomena. A total of 104 thyroid nodules with preoperative FNAC which were diagnosed as FACHAC in resection specimens were included in this study. Of these, 66 cases had also undergone thyroid core needle biopsy (CNB); FNAC and CNB DCs were compared in these cases. Various cytologic and histologic parameters were compared between the nodules with different FNAC DCs. After a review of FNAC slides, DCs were re-assigned in 20 (19.2%) out of the 104 cases. Of the 66 cases with CNB diagnoses which were mostly classified as lower DCs in FNAC, 31 (47.0%) were diagnosed as suspicious for a follicular neoplasm in CNB. Cases which were underdiagnosed in FNACs were associated with lower cellularity, predominant macrofollicular pattern, absence of microfollicles arranged in trabecular pattern, and absence of transgressing vessels in cytology smears. High cellularity, microfollicles arranged in trabecular pattern, nucleolar prominence, and large cell dysplasia were more frequently found in malignancy than in benign neoplasm. In conclusion, thyroid FACHACs seem to be under- and misdiagnosed in preoperative FNAC. Innate characteristics of the nodules were associated with under-diagnosis as well as the quality of the FNAC specimens. Certain cytomorphologic features can be helpful in differentiating malignancy among FACHACs.
Highlights
Ultrasonography (USG)-guided fine needle aspiration cytology (FNAC) is the most commonly used preoperative testing method for thyroid nodules
Types of architectural alteration reported in FN and Hurthle cell neoplasm (HN) were analyzed: the presence of architectural crowding, 3-dimensional branching pattern, microfollicles arranged in trabecular pattern, and transgressing vessels (Figs 1 and 2)
The presence of background colloid, especially watery colloid, was associated with diagnostic categories (DCs) II (p = 0.032) (Table 5). Compared to those cases with DC III (AUS), cases diagnosed as DC IV (SFN) were associated with higher cellularity, predominant microfollicular pattern, microfollicles arranged in trabecular pattern, and transgressing vessels (Table 5)
Summary
Ultrasonography (USG)-guided fine needle aspiration cytology (FNAC) is the most commonly used preoperative testing method for thyroid nodules. Thyroid FNAC is diagnostic in a majority of benign nodules as well as in most papillary thyroid carcinomas (PTCs) and other types of carcinomas, it generally functions as a screening test for follicular-patterned lesions. The cytologic findings of follicular adenoma (FA) and carcinoma, and Hurthle cell adenoma (HA) and carcinoma [FACHAC] can significantly overlap with various other thyroid follicular-patterned lesions including nodular hyperplasia, noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), and even follicular variant PTC [3,4,5]. TBSRTC suggests certain criteria for rendering DC IV (suspicious for a follicular neoplasm; SFN) to identify potential FTCs or HCs and to refer them for diagnostic lobectomy with higher sensitivity rather than higher specificity [1, 2], preoperative cytologic diagnosis of FACHAC remains challenging. Since FTC and HC can potentially progress to distant metastasis, it is important not to underdiagnose or misdiagnose these malignancies and prevent the treatment delay in patients with these tumors
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