Pitfalls in the diagnosis of fine needle aspiration cytology of the thyroid

Abstract

Objective: FineNeedleAspiration Cytology (FNAC) of the thyroid is a reliable, simple, minimally invasive, cost effective procedure with a high sensitivity, specificity and diagnostic accuracy. It is commonly used for the pre-operative assessment of thyroid lesions and as a guide to management. The aim of the study was to assess the accuracy of fine needle aspiration of the thyroid and critically evaluate the cases which showed discordance between cytology and histopathology. Material and Method: A total of 522 patients with thyroid swelling were aspirated during a four-year study period. Cases showing cytological and histological disparity were re-evaluated for the detection of possible causes of discrepancy. Results: In our study, cytohistological concordance was achieved in 97.8% of the cases. The sensitivity was found to be 72%, specificity 93.5%, positive predictive value was 78.3%, negative predictive value was 91.1% and total accuracy was 97.8%. False positives accounted for 5.4% and false negatives for 7.6% of the cases. Suboptimal material, lack of extensive sampling and absence of the characteristic nuclear features causing underdiagnoses of papillary carcinoma were recognized as common pitfalls. Too much emphasis on cellularity and architectural pattern led to the erroneous false positive diagnoses of malignancy. Too much stress on only one nuclear criteria or focal nature of the features can lead to a misdiagnosis of papillary carcinoma. Conclusion: Strict adherence to adequacy criterion and extensive sampling are of paramount importance in reducing false positive and negative cases.