Thyroid cytology in Pakistan; an institutional audit of AUS/FLUS category.

BACKGROUND: Fine needle aspiration cytology (FNAC) along with the thyroid ultrasound is an important tool in evaluation of the thyroid nodules & help in further management of these patients i-e decision of surgical intervention vs follow-up. The Bethesda system for reporting thyroid cytopathology (TBSRTC) category III of Atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) has risk of malignancy ranging from 5-15%. The aim of the present study was to describe the frequency of AUS/FLUS in thyroid gland FNACs and the surgical outcomes of these cases.

METHODS: The integrated laboratory management system (ILMS) retrieved the thyroid FNACs from 2010-2018 and subsequent surgical pathology specimens. For the AUS/FLUS cases, data regarding patients' demographics, cytology and histological diagnoses were recorded. The results were tabulated as the overall frequency of AUS/FLUS in thyroid FNACs, cytohisto correlation (benign and malignant) and risk of malignancy (ROM).

RESULTS: During 9-years, 256 (10.9%) cases out of 2342 thyroid FNACs were reported as AUS/FLUS at our institution. Mean age was 43.5 year. Majority (70.3%) of patients were female. Seventy-two of 104 resection specimens (69.2%) were reported benign and 32 cases (30.7%) had malignant diagnosis. Upper-bound ROM was 30.7% (32 cases with malignant diagnosis out of 104 resection specimens). Lower-bound ROM was calculated as 12.5% (32 cases with malignant diagnosis out of 256 total AUS diagnosis).

CONCLUSION: The AUS/FLUS category of thyroid cytology & associated risk of malignancy remain an evolving area of thyroid cytology. Individual institution should monitor the frequency & include ROM in the dashboard indicators to remain within the recommended range.