O‐7 AUDIT OF THYROID FINE NEEDLE ASPIRATION CYTOLOGY: A PROBABILISTIC APPROACH

  Recent proposals from the Papanicolaou Society of Cytopathology for reporting fine needle aspiration (FNA) specimens from thyroid nodules suggest using 6 cytodiagnostic categories. This probabilistic approach to detection of malignancy seeks to clarify clinical implications for individual categories. Our audit aims to determine the rates for neoplasia and malignancy in the five diagnostic categories currently used in our department. We have evaluated the effect of refining cytodiagnosis in the aspirates reported as equivocal. Methods:  A total of 392 thyroid FNA specimens reported between Jan 2003 and Dec 2005 were classed as inadequate, benign, equivocal, suspicious and malignant. 85 follow‐up thyroidectomies were received during this period; the histological diagnoses were correlated with the initial FNA diagnosis. Results:  The FNA diagnoses for the 85 thyroidectomies were: 7 inadequate, 37 benign, 31 equivocal, 5 suspicious for malignancy and 5 malignant. The rates for neoplasia and cancer were respectively: Inadequate: 2/7 (28.5%) & 0/7(0%) Benign: 4/37(10.8%) & 2/37(5.4%) Equivocal: 18/31(58.1%) & 11/31(35.4%) Suspicious: 4/5(80%) & 4/5(80%) Malignant: 5/5(100%) & 5/5(100%) On subdividing the category equivocal into: (1) Cellular lesion cannot exclude follicular neoplasm: the neoplasia rate was 4/12(33.3%) and the cancer rate 3/12(25%) (2) Follicular neoplasm/lesion with nuclear atypia: the neoplasia rate was 14/19 (73.7%) and the cancer rate 8/19 (42.2%) Excluding microcarcinomas, the false negative rate was 2.7%; there were no false positives. Conclusion:  The diagnostic certainty of cancer for FNA thyroid reported suspicious or malignant is high. If cytology is equivocal, thyroidectomy is appropriate for those reported follicular neoplasm ± nuclear atypia while repeat FNA is more suitable for cellular lesions where a follicular neoplasm is not the primary cytodiagnosis. neoplasm is not the primary cytodiagnosis.