Ultrasonographic and cytopathological features of an inflammatory pseudonodule in the thyroid gland

No previous study has investigated the ultrasonography (US) and cytopathological features of an inflammatory pseudonodule (IFP) associated with underlying thyroiditis. This study aimed to evaluate and identify the characteristic US features of IFP in patients who underwent US-guided fine-needle aspiration (US-FNA).

From January 2012 to December 2014, 899 patients underwent US-FNA for a solid thyroid nodule that was ≥5 mm in diameter, by a single radiologist. Among them, 49 nodules showed lymphocytic thyroiditis on cytological analysis. Based on cytohistopathological and follow-up US results, 28 IFP cases were included. The same radiologist and a cytopathologist retrospectively analyzed all the US images and the cytology slides, respectively.

The locations of 28 IFPs were from the right lobe (n = 13), left lobe (n = 13), and isthmus (n = 2). The echogenicity of 28 IFPs was hypoechoic (n = 5) or marked hypoechoic (n = 23). The common US features of IFP were marked hypoechogenicity, no calcification, smooth margin, ovoid shape, and the same vascularity as adjacent parenchyma. However, no IFP cases showed calcification, spiculated margin, taller-than-wide shape, and central or peripheral vascularity. The common cytopathological feature of IFP was lymphocyte infiltration, but the intensity of this was variable, with mild, moderate, and severe intensity observed in 8 (28.6%), 11 (39.2%), and 9 (32.1%) of cases, respectively.

IFP rarely showed malignant US and cytopathological features, except for marked hypoechogenicity, and these findings may be helpful for US and cytopathological diagnoses. Diagn. Cytopathol. 2016;44:725-730. © 2016 Wiley Periodicals, Inc.