OBJECTIVES:To determine the diagnostic accuracy of combined ultrasound-guided fine needle aspiration biopsy (USG-FNAB) and intraoperative frozen section examinationin (FSE) in diagnosing malignant thyroid nodules.
METHODOLOGY:Retrospective review of patients undergoing thyroidectomy with intraoperative frozen section examination following ultrasound guided fine-needle aspiration biopsy. Sensitivity, specificity, positive and negative predictive values and accuracy were calculated with respect to final histology.
RESULTS: A total of 2,239 nodules were subjected to USG-FNAB at the Diabetes, Thyroid and Endocrine Center, St. Luke's Medical Center between January 2007 and December 2009. Two hundred fifty-one nodules were surgically excised following USG-FNAB. Frozen section examinations were taken from 90 of 251 nodules. The USG-FNAB yielded 90.3% (n=1,721) adequate specimens and 9.7% (n=185) inadequate specimens. The histologic examination of the 251 surgically excised nodules revealed 182 (73%) benign and 69 (27%) malignant nodules. The sensitivity, specificity, positive and negative predictive values and accuracy rate of USG-FNAB cytology are 70.3%, 92.8%, 76.5%, 90.4% and 87.2%, respectively. The diagnosis by frozen section was benign in 56 cases (62%), malignant in 10 cases (11%) and deferred in 24 cases (27%). By FSE, the sensitivity, specificity, positive and negative predictive values and accuracy rate are 83.3%, 100%, 100%, 96.4% and 96.7%, respectively. A diagnostic accuracy of up to 97.2% was achieved when USG-FNAB and FSE were combined and when their findings were concordant. When USG-FNAB and FSE diagnoses were discordant, the FSE showed superior accuracy (83.3%) than cytology (16.7%). In the group of nodules with indeterminate or inadequate cytology, the diagnostic accuracy of frozen section is 100%.
CONCLUSION:Ultrasound guided fine-needle aspiration biopsy is an accurate preoperative test for the evaluation of nodular thyroid disease. It helps to distinguish malignant from benign lesions. The intraoperative frozen section is a valuable test for confirming the cytologic diagnosis. It is especially important in identifying malignant thyroid nodule in cases with indeterminate cytology. The combination of USG-FNAB and FSE greatly improves the accuracy rate in thyroid cancer detection.