OBJECTIVE. We aimed to establish the malignancy rate of thyroid nodules initially characterized as atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) and whether they differ according to histologic subcategory. We also investigated the value of ultrasound features that predict malignancy and BRAFV600E mutation analysis and suggest strategies for the management of AUS/FLUS nodules.
MATERIALS AND METHODS. A total of 165 AUS/FLUS nodules were investigated. There are nine histologic subcategories of AUS/FLUS nodules. We compared the risk of malignancy in thyroid nodules according to the histologic subcategory using ultrasound findings and of those exhibiting the BRAFV600E mutation.
RESULTS. The malignancy rate of nodules with an initial diagnosis of AUS/FLUS was 55.2% (91/165). The malignancy rates by histologic subcategory were 0% in groups 1 (0/2), 2 (0/3), 4 (0/3), 7 (0/3), and 8 (0/1); 76.5% (13/17) in group 3; 83.1% (59/71) in group 5; and 29.2% (19/65) in group 9. The malignancy rate of nodules with suspicious ultrasound features was 79.3% (73/92), and the malignancy rate of nodules with indeterminate ultrasound features was 24.7% (18/73). AUS/FLUS nodules exhibiting taller-than-wide shape, illdefined margins, and microcalcifications or macrocalcifications showed significantly higher odds ratios. The likelihood of BRAFV600E mutation–positive nodules showing malignancy was 97.5% (39/40), whereas 39.7% (25/63) of BRAFV600E mutation–negative nodules were malignant (p < 0.05).
CONCLUSION. The malignancy rate of AUS/FLUS nodules in our study cohort was higher than previously reported. Nodules with suspicious features on ultrasound had a higher malignancy rate than did those with indeterminate features on ultrasound. The malignancy rate differed according to histologic subcategory; therefore, management of AUS/FLUS nodules should be tailored according to histologic subcategory.
Keywords: Bethesda System for Reporting Thyroid Cytopathology, BRAFV600E mutation, thyroid gland, thyroid nodules, ultrasound
OBJECTIVE. Fine-needle aspiration biopsy (FNAB) is the current primary test to risk stratify thyroid nodules. However, in up to one third of biopsies, cytology is indeterminate. The Bethesda System for Reporting Thyroid Cytopathology categorizes thyroid cytology findings into six groups, with each group assigned a putative malignancy risk. This article reviews the Bethesda System, emphasizing the key facts necessary to understand thyroid biopsy results and effectively manage patients after FNAB.
CONCLUSION. It is important to diagnose and stratify the risk of malignancy in thyroid nodules. A working knowledge of the Bethesda System permits accurate, evidence-based risk stratification of patients with thyroid nodules and thereby facilitates their management. Because it is a uniform diagnostic approach, the Bethesda System allows comparisons of different management strategies across different institutions.
Keywords: atypia of undetermined significance (AUS), Bethesda System for Reporting Thyroid Cytopathology, cytology, fine-needle aspiration biopsy, follicular lesion of undetermined significance (FLUS), follicular neoplasm, nondiagnostic thyroid biopsy, thyroid
Presented at the 2012 annual meeting of the Radiological Society of North America, Chicago, IL.