Fine Needle Aspiration Cytology of Thyroid Nodules: Evaluation of Diagnostic Accuracy

Abstract 

Objective

The aim of this study was to evaluate the results of thyroid fine needle aspiration cytology (FNAC) and identify reasons for discrepancies between the cytological and histological diagnoses in our institution.

Materials and Methods

We evaluated the results of 1064 FNACs obtained from 737 patients, of which 98 underwent subsequent thyroid surgery.

Results

Histological analyses revealed that benign diagnoses based on FNAC were correct in 76 of the 80 benign cases (95%), with four cases being underdiagnosed (false negatives). Two of the four cases were due to incidental findings of papillary microcarcinomas. The third case was due to a cytologic sampling error and the fourth was due to cytologic underdiagnosis. Furthermore, malignant diagnoses based on FNAC were correct in 17 of the 18 malignant cases (94%), with one case being over-diagnosed (false positive) due to over-interpretation of Hürthle cells as carcinomatous cells. The accuracy, positive predictive value, and negative predictive value were 94.9%, 94.4%, and 95.0%, respectively.

Conclusion

Overall, FNAC is a sensitive and specific method for the pre-operative screening of thyroid nodules. However, due to limitations under some specific circumstances, such as papillary microcarcinoma, bizarre Hürthle cells, follicular neoplasm and technical difficulty during the aspiration, the management of thyroid nodules must not only depend on the results of FNAC but should also be correlated with clinical findings before surgical intervention.

Keywords:  Accuracy , Fine needle aspiration cytology , Sensitivity , Specificity , Thyroid nodule

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