Diagnosis of occult thyroid carcinoma by thyroid ultrasonography with fine needle aspiration cytology

OBJECTIVE: To assess the role of ultrasonography and fine needle aspiration cytology (FNAC) in preoperative diagnosis of patients with occult thyroid carcinoma (OTC). STUDY DESIGN: Data on 768 thyroid carcinoma patients receiving primary treatment at Chang Gung Medical Center were retrospectively reviewed. Of these patients, 97 had OTC. To detect small thyroid nodules early and define the characteristics of clinically palpable nodules, thyroid ultrasonography with FNAC were performed on 67 histopathologically proven OTC patients. Analysis for diagnostic value was done for ultrasonography and FNAC. RESULTS: In the 67 patients receiving ultrasonography with FNAC, 23 were preoperatively diagnosed as having papillary thyroid carcinoma and 1 as having follicular carcinoma. The tumor size of these 24 preoperative FNAC-proven OTC was 0.81±0.23 cm (mean±SD). In the remaining patients, 10 presented pictures suspicious for malignancy, with a mean tumor size 0.63±0.24 cm, and 33 (49.3%) were diagnosed as having benign thyroid lesions in preoperative FNAC. The tumor size in these 33 lesions was 0.58± 0.24 cm. Fifty-seven of the 67 OTC patients received frozen sections. Thirty-eight papillary thyroid carcinomas and four follicular carcinomas were correctly diagnosed on frozen sections. CONCLUSION: Although the rate is not high, high-resolution ultrasonography and FNAC is the best approach to preoperative diagnosis for OTC patients today.