Evaluation of the positive predictive value of atypical thyroid cytology cases according to the Bethesda system taking histopathology as gold standard.

Abstract

Objectives: For the past 20 years Fine Needle Aspiration Cytology (FNAC) has evolved as the most sensitive diagnostic tool for the initial screening of patients with thyroid nodules. Unfortunately FNAC is complicated by a recognized false negative rate of approximately 5%. The clinicians could face the difficulty in the management of patient when a cytological diagnosis is atypical only. The objective of study is to evaluate the positive predictive value (PPV) of atypical thyroid cytology cases according to the Bethesda system taking histopathology as gold standard. Study Design: Cross sectional study. Setting: Department of Pathology at Shaikh Zayed Hospital, Lahore. Period: Six months i.e. from 25.11.2014 to 25.5.2015. Materials and Methods: Patients presenting with solitary thyroid nodules in the outpatient department and fulfilling the inclusion criteria were included after evaluation by thyroid function tests and thyroid scan, FNAC was performed and reported according to Bethesda system of thyroid reporting. Later on, cases underwent lobectomy, total or hemi-thyroidectomy, the tissue was received in 10% formalin solution in our pathology department and then processed, stained and examined. FNAC results of atypical cases were then compared with the definitive histological diagnosis which were considered the gold standard. The slides were examined and any differences were sought by consensus of two pathologists. Eighty cases were observed with 95% confidence level, 11% margin of error, using non-probability purposive sampling technique for sample collection. Data was analyzed by SPSS version 15 (P value <0.05). Results: The mean age of patients was 38 years with SD ± 2.16. There were 22 (28%) males and 58 (72%) females in our study. In this study, positive predictive value for Atypia of undetermined significance/ Follicular lesion of undetermined significance (AUS/FLUS), follicular neoplasm (FN), suspicious for malignancy and positive for malignancy were 33.3%, 25%, 66.6% and 100% respectively. Overall PPV of atypical cytology was 35.71%. Overall accuracy of FNAC was 86.30%, 87.50% sensitivity and 86.15% specificity, PPV value 43.75% and negative predictive value was 98.25%. Conclusion: Results showed that Bethesda system of reporting is helpful for the management of patients who falls in to undetermined categories as it categorically divide atypical cytology cases in to three definite categories  AUS, FN and suspicious for malignancy and these categories have different risks of malignancy. Thus can help to determine a better patient outcome due to proper clinical management of thyroid swellings.