follicular lesions of undetermined significance

In 2010, the British Thyroid Association proposed a 5- to 8-tiered terminology, and the US National Cancer Institute published the Bethesda System For Reporting Thyroid Cytopathology (BSRTC) with 6 categories:
 benign;
 follicular lesion of undetermined significance/atypia of undetermined significance (FLUS/AUS);
 follicular neoplasm/follicular neoplasm Hürthle-cell variant;
 suspicious for malignancy;
 malignant;
 nondiagnostic (unsatisfactory).

The BSRTC is the only system that gives a detailed description of the diagnostic criteria (“the Bluebook”), the expected risk of malignancy for each category, and recommendations for management.

The FLUS/AUS category is heterogeneous in including cases for which the cytological findings are not convincingly benign. It is associated with an estimated risk of malignancy between 5% and 15%, so only a few patients should undergo surgery. (23634318 )

This category was recommended to represent no more than 7% of thyroid FNA reports. The first published studies suggested great variability in the application of this category, with percentages ranging from 2.5% to 28.6% of the FNA. (23634318 )

Reference

 Diagnosis of follicular lesions of undetermined significance in fine-needle aspirations of thyroid nodules. Ratour J, Polivka M, Dahan H, Hamzi L, Kania R, Dumuis ML, Cohen R, Laloi-Michelin M, Cochand-Priollet B. J Thyroid Res. 2013;2013:250347. doi : 10.1155/2013/250347 PMID: 23634318 [Free] http://www.hindawi.com/journals/jtr/2013/250347/