Ultrasound (US)-guided fine-needle aspiration biopsy (FNAB) is an accurate, reliable, and simple procedure to perform, and it is nowadays accepted as a standard diagnostic method for the differential diagnosis of thyroid nodules. However, a major limitation of US-FNAB is indeterminate cytology results at a thyroid nodule. This study investigated the clinical and US characteristics that predict malignancy, as well as the role of intraoperative frozen sections (FS) in the treatment of thyroid nodules with indeterminate cytology.

From September 2002 to December 2007, the medical records of 181 patients (185 nodules) with indeterminate FNAB cytology results were retrospectively reviewed. Among them, 99 patients (M:F = 13:86; mean age, 43.71 years) with 99 thyroid nodules underwent subsequent surgery with pathologic confirmation. Seventy-eight patients (78.8%) underwent intraoperative FS. US findings of the surgically proven thyroid nodules were retrospectively reviewed. US features, clinical characteristics, and FS results were compared to the surgically proven pathologic results.

Nineteen nodules (19.2%) with indeterminate FNAB cytology were diagnosed as malignant. Lesion size varied from 4 to 70 mm (mean, 27.0 mm). Male patients (46.2%) were more significantly associated with malignancy than female patients (15.1%, P < 0.05). Microlobulated or ill-defined margins (87.5%), microcalcifications (50.0%), and taller-than-wide shape (80.0%) were US features showing correlations with malignancy (P < 0.05). Intraoperative FS significantly predicted malignancy (P < 0.05). Of the 78 cases with FS, 29 cases (37.2%) were deferred. Among the remaining 49 cases, 4 (5.1%) were malignant on FS and subsequent surgical pathology. Forty-five cases (57.7%) were diagnosed as benign on FS, but only two cases were diagnosed as malignant on surgical pathology.

Ultrasound is a feasible method in predicting malignancy in thyroid nodules with indeterminate FNAB cytology. Also, intraoperative FS is a supportive method with high specificity that may guide the treatment of thyroid nodule with indeterminate cytology.