Background: Hurthle cell/oncocytic change is commonly reported on thyroid fine-needle aspiration (FNA) and may be considered an "atypical cell" by clinicians. This study aims to delineate the association between Hurthle cells in preoperative cytology and subsequent pathology of the indexed thyroid nodule and to report rates of malignancy.

Methods: Retrospective review of records of 300 patients with Hurthle cell/oncocytic change on FNA and final surgical pathology at a tertiary referral center between 2000 and 2013 was performed and compared with a multi-institutional FNA cohort. The degree of Hurthle cell presence was correlated with histopathologic diagnoses.

Results: In the Hurthle cell FNA group, Bethesda System for Reporting Thyroid Cytopathology (BSRTC) categories were as follows: I (nondiagnostic) 14 (4.7%); II (benign) 113 (37.7%); III (atypia of undetermined significance/follicular lesion of undetermined significance) 33 (11%); IV (follicular neoplasm/suspicious for a follicular neoplasm) 125 (41.6%); V (suspicious for malignancy) 12 (4%); and VI (malignant) 3 (1%). When categorized based on the degree of Hurthle cell change, 59 (29%) were classified as mild, 13 (6%) moderate, and 131 (65%) as predominant. When comparing the results with a multi-institutional FNA cohort (all with surgical confirmation), the presence of Hurthle cells was found to be associated with a lower risk of malignancy in all BSRTC categories, with a statistically significant difference in the BSRTC IV and V groups. The sole exception was when Hurthle cell presence was classified as predominant (defined as > 75% of the cellular population); the rate of malignancy was significantly elevated in FNAs interpreted as benign/Bethesda II.

Conclusions: Although Hurthle cells have been considered by clinicians as an "atypical cell," their presence does not increase the risk of malignancy within BSRTC categories overall. However, when predominant Hurthle cell change is present, the risk of malignancy is increased in the benign cytology/BSRTC category II.