BACKGROUND Atypia or follicular lesions of undetermined significance (AUS/FLUS) is a broad cytological category in the Bethesda system for classifying thyroid cytology. This study investigated the diagnostic accuracy of ultrasound (US) analysis of thyroid nodules with AUS/FLUS.

PATIENTS AND METHODS Of 5062 subjects with nodules subjected to fine-needle aspiration cytology (FNACs) at our institution from January 2010 through May 2012, 383 met the Bethesda criteria for AUS/FLUS. After excluding subjects who had a history of thyroid cancer, who only underwent repeat FNA or who underwent no further examinations, we selected 249 subjects who had subsequently undergone a core-needle biopsy and/or surgery. Of these, 100 were found to have malignant nodules (40·2%), 122 had benign nodules (49%), and 27 had nodules with indeterminate status (10·8%). We compared specific US parameters, including size, location, content, shape, margin, echogenicity, echotexture and calcification across these subject groups.

RESULTS Multivariate analysis revealed that malignancy was associated with taller-than-wide shape (TDW) (OR = 8·43, P = 0·002), ill-defined margin (OR = 3·23, P = 0·002) and marked hypoechogenicity. (OR = 3·61, P = 0·001). The specificity and positive predictive values of TDW were 98% and 90·6%,respectively. The specificity and positive predictive values of 'TDW and marked hypoechogenicity' were both 100%.

CONCLUSION US findings play a complementary role in the diagnosis of thyroid nodules with AUS/FLUS. In case of highly suspicious US findings such as 'TDW and marked hypoechogenicity', could be very helpful in the diagnosis of malignancy.