Thyroid nodule other diagnostic studies
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Other Diagnostic Studies
Fine needle aspiration
The most important diagnostic test to differentiate thyroid nodules from each other is fine needle aspiration (FNA). As FNA is considered as an aggressive procedure, the American Thyroid Association developed the following criteria for FNA indication:
- Nodules ≥ 1 cm with intermediate or high suspicion US pattern
- Nodules ≥ 1.5 cm with low suspicion US pattern
- Nodules ≥ 2 cm with very low suspicion US pattern (e.g., spongiform). Observation an alternate option
- For nodules that do not meet the above criteria, FNA is not required, including nodules < 1 cm (with some exceptions) and purely cystic nodules 26462967
Molecular marker evaluation
The molecular marker evaluation tests are performed using samples that are collected during fine needle aspiration, from needle washings.
The most important indications of the molecular markers study include indeterminate cytological diagnosis, to assist with decision making about management option (surgical treatment). The molecular tests which have the most available data are: Afirma Gene-expression Classifier [68], seven-gene panel of genetic mutations and rearrangements [69] and galectin-3 immunohistochemistry [70].
The Afirma gene-expression classifier (167 GEC; mRNA expression of 167 genes) evaluates for the presence of benign gene expression profile. It has a high sensitivity (92 %) and negative predictive (93 %) value but low positive predictive value and specificity (48–53 %) [68, 71]. It is used as a rule out test to identify benign nodules. A benign GEC result predicts low risk of malignancy but the nodules classified as benign still have ~5 % risk of malignancy [71, 72].
The seven gene mutation and rearrangement analysis panel evaluates for BRAF, NRAS, HRAS and KRAS point mutations and common rearrangements of RET/PTC and PAX8/PPARγ. It has a high specificity (86–100 %) and positive predictive value (84–100 %) but poor sensitivity (reported from 44 to 100 %) [69, 73–75]. It is being used as a rule in test for thyroid malignancy.