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Ultrasound-Pathology Discordant Nodules on Core-Needle Biopsy: Malignancy Risk and Management Strategy.

BACKGROUND
The reported malignancy rates of thyroid nodules that appear suspicious on ultrasound (US) but yield benign fine-needle aspiration (FNA) cytology results range from 13.6% to 56.6%. However, the malignancy risk of nodules that are discordant on US and core-needle biopsy (CNB) pathological findings has not been evaluated. This study evaluated the malignancy risk associated with thyroid nodules that are suspicious on US but yield benign CNB results.


METHODS
Between July 2008 and November 2011, 1309 patients with 1313 thyroid nodules underwent US-guided CNB. Among these, 166 thyroid nodules that were suspicious on US but yielded benign CNB results were retrospectively reviewed. Benign nodules were diagnosed by surgery, FNA, and/or CNB that was repeated at least twice or CNB and lesion size stability on follow-up. The malignancy risk of US-pathology discordant nodules was calculated according to recommendations by Moon et al., and a further evaluation was conducted using four different US risk systems. Factors that differentiated benign from malignant nodules were assessed using the chi-square test or Fisher's exact test. Moreover, the histological findings of US-pathology discordant nodules were analyzed.


RESULTS
Patients with benign and malignant nodules did not differ significantly regarding clinical and demographic characteristics. Of the 166 US-pathology discordant nodules, seven (4.2%) were confirmed malignant. The malignancy risks associated with the five US risk systems ranged from 3.6% to 5.5%. Regarding suspicious US features, only the number of suspicious features was associated with malignancy (p = 0.002). Histological analysis of benign CNB specimens with suspicious US features revealed fibrosis (77.6%), thyroiditis (28.7%), calcifications (10.6%), and hemosiderin deposition (6.4%).


CONCLUSIONS
The malignancy risk among thyroid nodules with discordant US and CNB results ranged from 3.6% to 5.5%, depending on US risk systems. However, repeated biopsy may be necessary for selected thyroid nodules with more than two suspicious US features.