Fine-Needle Aspirates of Thyroid Microcarcinoma

Abstract

Introduction Widespread use of ultrasound allows for detection of smaller thyroid nodules and preoperative evaluation with fine-needle aspiration (FNA). Both incidental and non-incidental microcarcinoma can be found, leading to uncertainty with clinical management. Materials and methods A retrospective analysis of thyroid FNAs performed at our institution was conducted for the 5-year period from 2010 to 2014. Aspirates were categorized using the Bethesda System for Reporting Thyroid Cytopathology. Cytologic diagnoses were then correlated with final histopathology. Among samples with malignancy on surgical resection, nodules were stratified by size. Results A total of 2531 thyroid FNAs were identified; 587 samples had histologic correlation, and 259 malignancies were reported. They were separated into nodules >1 cm (n = 144, 56%) and ≤1 cm (n = 115, 44%). Microcarcinoma was further subdivided into incidental (size ≤0.5 cm, n = 55, 48%) and non-incidental (size >0.5 cm and ≤1 cm, n = 60, 52%). The preoperative cytologic diagnoses for incidental microcarcinoma were: benign (B, n = 11, 20%), follicular lesion of undetermined significance (FLUS, n = 15, 27%), follicular neoplasm (FN, n = 11, 20%), suspicious for malignancy (SM, n = 7, 13%), malignant (M, n = 8, 15%), and nondiagnostic (ND, n = 3, 5%). The FNA categories for non-incidental microcarcinoma were: B (n = 13, 22%), FLUS (n = 3, 5%), FN (n = 3, 5%), SM (n = 10, 17%), M (n = 29, 48%), and ND (n = 2, 3%). Conclusions Incidental microcarcinoma is not an uncommon entity, making up 21% (55 of 259) of malignant nodules on thyroidectomy. Indeterminate diagnoses (FLUS + FN + SM) accounted for the majority (60%) of preoperative FNAs for incidental microcarcinoma, compared with 27% for those of non-incidental microcarcinoma (P < 0.05, χ2 test).