Study of intrathyroid fat-containing lesions using CT imaging with literature review

Introduction: This study was conducted to estimate the incidence of intrathyroid fat-containing lesions based in the general population on CT imaging. The imaging characteristics of the lesions on CT were also analyzed. Methods: This retrospective study included data for 1,205 patients who underwent neck CT at our institution from January 2012 to January 2013. Data concerning size, shape, homogeneity of attenuation and location of lesions, and the presence of a fatty band connecting to extrathyroid fat were evaluated. Pathologic specimens were reevaluated when available. A literature review was conducted based on 16 peer-reviewed articles describing intrathyroid fat-containing lesions. Results: Intrathyroid fat-containing lesions were detected in 13 patients (1.2 %). The mean lesion size was 5.7 mm (range, 2.6-10.6 mm). Nodular shape (92 %), homogeneous attenuation (92 %), and the fatty band (77 %) were common CT features. Posterior (85 %), medial (85 %), and upper (92 %) aspects of the thyroid gland were most commonly involved. In four patients who underwent surgery, one had fat-containing nodular hyperplasia, one had ectopic thymic tissue within mature fat, and one had mature fat itself. In 16 previously reported studies, the 41 lesions presented two fat infiltration patterns, diffuse (n = 12) and localized (n = 29), and two lesions showed mature fat tissue itself. Conclusion: Intrathyroidal fat-containing lesions were found in 1.2 % of patients presenting for neck CT. Almost all of the lesions occurred in common locations and showed similar features on CT, including nodular shape, homogeneous attenuation, and a fatty band.