"Hurthle Cell Lesion": A Clinicopathologic Study and Significance of Cytological Diagnosis

Introduction: Since the 2008 publication of the Bethesda terminology for thyroid cytopathology, diagnosis rates of atypia of undetermined significance (AUS) from 2.1% to >10% have been reported. Although a majority with benign follow-up prove to be adenomatous nodules, some show lymphocytic thyroiditis (known to be associated with cytologic atypia) on follow up. We sought to examine the proportion of AUS with a follow-up of lymphocytic thyroiditis, and if features could be identified that were characteristic of thyroiditis-associated atypia, allowing for increased comfort in the diagnosis of lymphocytic thyroiditis and a decrease in AUS. Materials and Methods: The pathology database was searched for thyroid FNA’s with an interpretation of AUS from the implementation of the Bethesda system in 2010 to 2013. The AUS rate was determined, and cytologic and/or surgical follow-up was identified. Original and follow-up slides were reviewed. Results: 86 AUS cases (6% of total thyroid FNA) were identified (61 with cytologic and/or surgical follow-up) with 61% having benign follow-up, 30% malignant follow-up, and 6% remaining as AUS on follow-up. 15% had a diagnosis of Hashimoto’s or lymphocytic thyroiditis alone (4 cases), with papillary thyroid carcinoma (PTC, 2 cases), or with incidental microcarcinoma (3 cases, PTC felt not to be represented on review of smears). Features that led to an AUS interpretation in the setting of thyroiditis were identified, including nuclear enlargement, elongation, crowding and grooves (as seen in Figure 1). Features supporting thyroiditis-associated atypia included degenerated cytoplasm, coarse chromatin, and prominent central nucleoli. Sparse malignant cells admixed with oncocytes and a polymorphous lymphoid population, including large immature lymphs, inhibited definite diagnosis in 2 cases where PTC co-existed with Hashimoto’s. Conclusions: We found an AUS rate of 6%, with 15% associated with lymphocytic thyroiditis. Increased recognition of these sometimes subtle features could lead to a decrease in the overall AUS rate.