Oncocytic follicular nodules of the thyroid with or without chronic lymphocytic thyroiditis: An institutional experience

Background: Oncocytic follicular (OF) cells can be a prominent component of fine needle aspiration (FNA) specimens from neoplasms (adenomas and carcinomas) and nodules arising in multinodular goiter and chronic lymphocytic thyroiditis (CLT). Because OF cells can be present in non-neoplastic and neoplastic thyroid lesions it can be challenging to differentiate between these two in FNA specimens. The aims of this study were to determine the risk of malignancy in cases diagnosed as either oncocytic follicular neoplasm (OFN) or hyperplastic/adenomatoid nodule with OF on FNA and to identify clinicopathologic features that may help in predicting malignancy in such cases, especially the presence or absence of CLT. Design: We retrospectively searched the computerized laboratory information system at our institution between 1998 and 2009 for thyroid US guided FNA specimens in which the term “oncocytic/oncocytes” was mentioned in the final cytopathologic diagnosis. A total of 340 cases were selected for this study. The following data points were collected: Patient demographics, site of thyroid biopsy, size of lesion, FNA diagnosis, histopathologic follow-up and presence of CLT. Surgical pathology follow-up (SPFU) was available in 269 (79%) cases. Results: Two hundred and sixty patients were females and 80 males (average age 53 years). The lesion size was <3.0 cm in 241 (71%) and ≥ 3.0 cm in 99 (29%) cases. Cytologic diagnoses included: Follicular neoplasm with oncocytic features (FNOF) 321 and suggestive of FNOF 19 cases; a secondary cytologic diagnosis of CLT was made in 20 cases. SPFU was available in 269 (79%) cases; it was benign in 213 (213/267 = 79%) and malignant in 56 (56/269 = 21%) cases. The background thyroid showed CLT in 67 (25%) cases; 24% (48/196) neoplasms occurred with versus 76% (147/196) without CLT. The rate of malignancy was lower in nodules measuring less than 3.0 cm as compared to those equal or greater than 3.0 cm in size (17% vs. 28% respectively). The presence of CLT did not significantly alter the rate of malignancy in both FNA and surgical pathology specimens. Conclusions: Based on this study, nodule size and not CLT appears to be an important clinicopathologic features in the management of thyroid FNA specimens diagnosed as OFN.