Clinical presentation: A 32-year-old woman was referred for a follow-up examination. She has been known harboring a thyroid nodule for more than 10 years. The lesion has gradually increased in size.

Palpation: a not very firm nodule in the right lobe.

Laboratory tests indicated euthyroidism (TSH 1.76 mIU/L).

Ultrasonography. The thyroid was moderately hypoechogenic and contained several more hypoechogenic small discrete areas. There was a (dominantly) hypoechogenic nodule showing halo sign and perinodular blood flow in the right lobe.  

Common ultrasound-cytological diagnosis: Hashimoto's thyroiditis. Suspicion of oxyphilic variant of follicular tumor.

Histopathology disclosed an oxyphilic adenoma and Hashimoto's thyroiditis both within the tumor and in the non-nodular part of the thyroid, as well.

Comments.

1. Although there are two features which might raise the suspicion of tumor, i.e. the relatively monomorphic pattern of oxyphilic cells and the presence of prominent nucleoli, the cytological pattern itself corresponds to a Hashimoto's thyroiditis.
   
2. If we take the ultrasound pattern into account, the situation changes. The nodule in question shows both sonographic signs of capsule which stands for a follicular type tumor.
   
3. Although the non-nodular part is also hypoechoic, the dominant part of the nodule is more hypoechoic. It means that irrespectively of the reference tissue, the dominant part of the nodule should be considered hypoechoic. The reference tissue has an influence whether this lesion should be considered as a dominantly hypoechoic, heterogeneous nodule or simply as a hypoechoic one because the echogenicity of the brighter islets within the nodule (right image, histogram value 64.9) are more echoic than the extranodular part (left image, histogram value 46.9) but less echoic than a healthy thyroid.