J Pathol Transl Med.  2020 Mar;54(2):171-178. 10.4132/jptm.2019.12.03.

Contribution of cytologic examination to diagnosis of poorly differentiated thyroid carcinoma

• Kim NR
• Seok JY
• Chung YS
• Lee JH
• Chung DH

• KMID: 2501607
• DOI: http://doi.org/10.4132/jptm.2019.12.03

Abstract

Background
The cytologic diagnosis of poorly differentiated thyroid carcinoma (PDTC) is difficult because it lacks salient cytologic findings and shares cytologic features with more commonly encountered neoplasms. Due to diverse cytologic findings and paucicellularity of PDTC, standardization of cytologic diagnostic criteria is limited. The purpose of this study is to investigate and recognize diverse thyroid findings of fine needle aspiration (FNA) cytology and frozen smear cytology in diagnosis of this rare but aggressive carcinoma.
Methods
The present study included six cases of FNA cytology and frozen smears of histologically diagnosed PDTCs.
Results
PDTC showed cytologic overlap with well-differentiated thyroid carcinomas (WDTCs). Five of six cases showed dedifferentiation arising from well differentiated thyroid carcinomas. Only one de novo PDTC showed highly cellular smears composed of discohesive small cells, high nuclear/cytoplasmic (N/C) ratio, prominent micronucleoli, and irregular nuclei. Retrospectively reviewed, these findings are highly suspicious for PDTC. Cytologic findings of nuclear atypia, pleomorphism, and irregularity were frequently found, whereas scattered small cells were seen only in the de novo case.
Conclusions
Heterogeneous cytologic findings of PDTCs are shared with those of WDTCs and contribute to difficult preoperative cytologic diagnoses. Most PDTCs show dedifferentiation from WDTCs. Albeit rare, de novo PDTC should be considered with cytology showing discohesive small cells with high N/C ratio. This will enable precise diagnosis and prompt treatment of this aggressive malignancy

Keyword

Cytology; Biopsy, fine-needle; Poorly differentiated thyroid carcinoma; Frozen sections

Figure

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  Fig. 1. Cytologic findings of poorly differentiated thyroid carcinoma. (A) Case 1. Fine needle aspiration (FNA) shows few clusters of follicular cells with atypia. (B–E) Case 2. (B) FNA shows few scattered sheets or singly scattered small cells with no nuclear inclusions or grooves. (C–E) Frozen imprint cytology of intraoperative excised mass shows round tumor cells containing scant cytoplasm and round heterochromatic nuclei (C, D). (E) High power view shows atypical follicular cells with small prominent nucleoli. (F) Case 3. FNA reveals cellular clusters of atypical follicular cells with irregular vesicular nuclei. (G) Case 4. FNA of case 4 shows few scattered clusters of follicular cells with mildly irregular nuclei. (H) Case 5. FNA of case 5 shows scant cellular smear with few microfollicles. (I, J) Frozen imprint smear of case 5 shows few papillary structures (I) with nuclear atypia and occasional nuclear inclusions (J). (K, L) Case 6. (K) FNA shows cluster of atypical follicular cells with prominent nucleoli. (L) Intraoperative frozen smears show scattered small cells with nuclear irregularities.

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  Fig. 2. Histology of resected poorly differentiated thyroid carcinomas. (A, B) Case 1. Mass with well-demarcated capsule filled with microfollicles with necrosis. (B) Necrosis. (C, D) Case 2. Histology shows large mass with solid growth pattern and multifocal necrosis in insular pattern (C). Frequent mitotic activity (D, left) and coagulation necrosis (D, right) are observed. (E) Case 3. Histology shows follicular carcinoma and intervening necrosis with focal poorly differentiated carcinoma (inset). (F) Case 4. Histology shows extensive necrosis in well-differentiated follicular carcinoma. Inset shows cellular atypia adjacent to necrosis. (G, H) Case 5. (G) Solid growth pattern in follicular carcinoma. (H) High power view shows necrosis with transition to poorly differentiated carcinoma. (I, J) Case 6. (I) Histology of total thyroidectomy shows background well-differentiated follicular carcinoma and foci of poorly differentiated carcinoma. (J) High power view (left) is shown. Note mitosis in tumor cells (right).

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