Original article / research
Diagnostic Accuracy of Fine needle Aspiration Cytology of Thyroid lesion by Bethesda System and its Histopathological Correlation: An Institutional Experience of Two Years
Lt. Brkm Govt Medical College Dimrapal C.G., Dimrapal, Jagdalpur Dist.- Bastar, Chhattisgarh, India.
Introduction: Fine Needle Aspiration (FNA) is a primary investigation for diagnosis and management of Thyroid lesions. But thyroid FNA suffers from reporting confusion due to multiplicity of category name and variable diagnostic terminology. To overcome this, National Cancer Institute (NCI) in 2007 introduced The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC), which provides standardised nomenclature along with Risk Of Malignancy (ROM) for each category.
Aim: (1) To classify Fine Needle Aspiration Cytology (FNAC) of thyroid lesion according to Bethesda System and calculate ROM for each category. (2) To find out accuracy of FNAC of thyroid lesion.
Material and Methods: A prospective study was conducted in the Department of Pathology, MKCG Medical College and hospital over a period of 2 years (2012-2014) which included 285 cases. FNA for Thyroid swelling were obtained from OPD and IPD of various departments of MKCG Medical College and Hospital Berhampur. Smears prepared in glass slide from aspirated material were stained using May Grunwald Giemsa (MGG) stains, Diff-Quik stain and Haematoxylin and Eosine (H&E) stain. All FNAC were classified according to TBSRTC 2007 guidelines into 6 categories as Cat I (Catagory 1)-Non Diagnostic/Unsatisfactory, Cat II-Benign, Cat III-Atypia of Undetermined Significance (AUS)/Follicular lesion of Undetermined Significance, Cat IV-Follicular Neoplasm/Suspicious for Follicular Neoplasm, Cat V- Suspicious for Malignancy and Cat VI- Malignant. The cytological findings were correlated with the histopathology in available cases. Statistical test used for the study was Z-Test. It is the likelihood that the test is correctly rejecting the null hypothesis. This study has 90% power means that the study has 90% chances of test having significant result.
Results: The distribution of FNA of 285 cases according to Bethesda System were CAT I to CAT VI as 05 (1.8%), 236 (82.8%), 11 (3.8%), 12 (4.2%), 07 (2.4%) and 14 (5%), respectively. Biopsy was available in 85 cases. The ROM reported on histopathological follow-up according to Bethesda System were CAT I 0 (0%), CAT II 2 (4.2%), CAT III 01 (14.2%), CAT IV 02 (20%),CAT V 04 (66.6%) and CAT VI 11 (100%). The Sensitivity, Specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV) and Diagnostic Accuracy were found to be 92%, 91.8%, 85.2%, 95.7% and 91.9%, respectively.
Conclusion: FNA is sensitive, specific and accurate initial investigation for evaluation of thyroid lesion but it needs a uniform reporting system for proper categorisation and management. Bethesda System is an excellent reporting system for Thyroid FNAC consisting of clear categorical nomenclature including ROM and proposed clinical management for each category which helps surgeon in preventing unnecessary surgery.
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