ES15P ATYPICAL FOLLICULAR’ FNAC – RELATIONSHIP WITH FINAL HISTOPATHOLOGY

Abstract

Background Fine needle aspiration cytology (FNAC) is a useful technique for the investigation of thyroid lesions. However, about 15% of FNAC results are classified as ‘atypical follicular’– a dilemma for the surgeon.Purpose To investigate the relationship between ‘atypical follicular’ FNAC results and final histolopathological diagnosis.Methodology Retrospective review of patients who underwent thyroid FNAC at the University of Sydney endocrine surgical unit.Results Study period – 1985 to 2005; Study population – 424 patients with an atypical FNAC and a malignancy on final histopathology. This accounted for 21% of all atypical FNAC results (n = 1956). Demographics – 342 females, 82 males with a mean age of 47.2 (SD 16.7). The most common presentation in this group was a single thyroid nodule n = 252, followed by multinodular goiter n = 155. Overall, 269 (63.4%) had papillary/mixed (papillary and follicular) carcinoma, 106 (25%) had follicular carcinoma and 49 (11.6%) other malignant pathology. Of the subjects with papillary cancers, 34% had papillary microcarcinoma. Demographics were not predictors of pathology. Over the study period of 20 years, no changes in the pattern of histopathology findings were noted.Conclusion Although the ‘atypical follicular’ FNAC has traditionally been considered to be either follicular adenoma or carcinoma, a great proportion of subjects actually have a papillary carcinoma demonstrated on histopathology. A significant proportion of this was accounted for by the presence of incidental papillary microcarcinoma.