J Pathol Transl Med.  2018 May;52(3):171-178. 10.4132/jptm.2018.04.03.

Cytologic Diagnosis of Noninvasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features and Its Impact on the Risk of Malignancy in the Bethesda System for Reporting Thyroid Cytopathology: An Institutional Experience

• Kim M
• Kim JE
• Kim HJ
• Chung YR
• Kwak Y
• Park SY

• KMID: 2412929
• DOI: http://doi.org/10.4132/jptm.2018.04.03

Abstract

BACKGROUND
This study was performed to analyze cytologic diagnosis of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) and its impact on the risk of malignancy (ROM) in the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC).
METHODS
Five thousand five hundred and forty-nine cases of thyroid fine-needle aspiration cytology (FNAC) diagnosed between 2012 and 2014 were included in this study. Diagnostic categories based on TBSRTC were compared with final surgical diagnoses, and the ROM in each category was calculated both when NIFTP was included in malignant lesions and when excluded from malignant lesions.
RESULTS
Of the 5,549 thyroid FNAC cases, 1,891 cases underwent surgical resection. In final diagnosis, 1,700 cases were revealed as papillary thyroid carcinoma (PTC), and 25 cases were reclassified as NIFTP. The cytologic diagnoses of NIFTP were non-diagnostic in one, benign in five, atypia of undetermined significance (AUS) in 14, follicular neoplasm in two, and suspicious for malignancy in three cases. Collectively, NIFTP/encapsulated follicular variant of PTC (EFVPTC) were more frequently classified as benign, AUS, or follicular neoplasm and less frequently categorized as malignant compared to conventional PTCs. Exclusion of NIFTP from malignant diagnoses resulted in a slight decrease in malignancy rates in non-diagnostic, benign, AUS, follicular neoplasm, and suspicious for malignancy categories without any statistical significance.
CONCLUSIONS
The decrease in the ROM was not significant when NIFTP was excluded from malignant lesions. In thyroid FNACs, NIFTP/EFVPTCs were mostly classified into indeterminate categories. Therefore, it might be feasible to separate NIFTP/EFVPTC from conventional PTC on FNAC to guide clinicians to conservative management for patients with NIFTP/EFVPTC.

Keyword

Thyroid; Fine-needle aspiration cytology; Encapsulated follicular variant of papillary thyroid carcinoma; Noninvasive follicular thyroid neoplasm with papillary-like nuclear features; Risk of malignancy; Bethesda system

MeSH Terms

Biopsy, Fine-Needle
Diagnosis*
Humans
Thyroid Gland*
Thyroid Neoplasms*

Figure

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  Fig. 1. A representative case of noninvasive follicular thyroid neoplasm with papillary-like nuclear features diagnosed as atypia of undetermined significance in fine-needle aspiration cytology. (A) Low power examination of cytology smear reveals small clusters and scattered single cells with low cellularity. (B) Small cell clusters showing nuclear enlargement and overlapping. (C) A cell cluster with microfollicles. Tumor cell nuclei show nuclear clearing, nuclear elongation and peripherally located micronucleoli. (D) In final histology, the tumor has a thick fibrous capsule with smooth border and shows a follicular growth pattern. (E) Follicles have densely eosinophilic colloid with peripheral scalloping and mutinucleated giant cells. (F) Tumor cells show papillary thyroid carcinoma–like nuclear features.

• 

  Fig. 2. A representative example of encapsulated follicular variant of papillary thyroid carcinoma with invasion classified as papillary carcinoma in fine-needle aspiration cytology. (A) Low power examination reveals large tissue fragments and small clusters in cytologic smear. (B, C) Monolayered sheets or syncytial clusters showing nuclear elongation, overlapping, loss of polarity and grooves. (D) In the final histology of surgical excision specimen, the tumor has a thick fibrous capsule with irregular border. (E) A focus of capsular invasion (arrow) is evident. (F) Tumor cells are arranged in microfollicular or trabecular pattern, showing typical papillary thyroid carcinoma–like nuclear features.

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