PITFALLS OF THYROID CYTOLOGY IN DUHOK-IRAQ

Background: The current study was undertaken to determine the validity of thyroid fine needle aspiration cytology (FNAC) in Duhok-Iraq to clarify its traded diagnostic errors locally and broadly. Patients and Methods: All thyroid cytologic and histologic cases referred to Duhok Pathology Centers, between January 2013 and December 2016, were enrolled in this study. Cytologic findings were compared with their corresponding final histologic results. The validity parameters of cytology were assessed and cases showing cytologic and histologic non-conformance were re-evaluated to highlight the dependant cytologic pitfalls used locally and in the literature. Results: Of 553 thyroid biopsies with 81.6% benign and 18.4% malignant, only 125 cases had preoperative diagnostic cytology and subsequent histologic final diagnoses. Of these, apart from 2 unsatisfactory cases, only 6 (4.9%) cytologic reports were proved not to be matched with their corresponding histologic results. The remaining 117 (95.1%) cases showed complete agreement between the two evaluation tests. Malignancy was predicted by cytology in 82.9%with a sensitivity of 94.3% and specificity of 95.5%. All the 6 unmatched cases were aspirated blindly with no image guide, 4 were false positive resulting in 3.2%false positive rate and 89.2% positive predictive value. The remaining unmatched 2 cases were false negative cytologies that gave 1.6% false negative rate and 97.7% negative predictive value. Cytologically, 5 (83.3%) unmatched smears, 4 false positive and 1 false negative, appeared in smears of lymphocyte-rich thyroid lesions, particularly Hashimoto’s. The false positive pitfalls comprised 2 over diagnosis of hypercellular smears showing some features of papillary carcinoma, 1 overestimation of the large cells with nuclear atypia as follicular carcinoma and 1 over diagnosis of lymphoid hyperplasia as lymphoma. On the other hand, low cellular smears with unclear atypical lymphoid cells underdiagnosed low grade MALT lymphoma and unobvious cytologic criteria missed the diagnosis of papillary carcinoma. Conclusions: Lymphocyte-rich thyroid smears should be interpreted by experienced cytopathologists in the context of clinical, radiological and cytologic findings as suchcases may give certain cytomorphologic pitfalls that may decrease the cytologic validity. In suspicious cases, further tests should be justified to overcome the limitations and pitfalls of features when applied alone. Duhok Med J 2019; 13 (1): 83-95.