Clinical presentation: A 50-year-old woman was referred for evaluation of a nodule detected on PET CT scan. The patient was operated on ductal invasive breast carcinoma two years ago. On scintigraphy the nodule did not take up iodine but did MIBI.

Palpation: a very firm nodule in the right lobe.

Functional state: euthyroidism (TSH 1.08 mIU/L).

On ultrasound, a hypoechogenic nodule was found corresponding to the palpable nodule. The lesion presented the so-called taller-than-wide sign and contained coarse calcification. There were other intranodular hyperechogenic granules within the lesion. These were probably comet-tail artifacts. The nodule displayed neither halo sign nor perinodular blood flow.

Aspiration cytology was performed from the nodule in the right lobe. The cytological pattern itself corresponded to a follicular lesion with atypia. We gave a common ultrasound-cytological diagnosis of suspicion of (papillary) thyroid carcinoma. A lobectomy was advised.

Histopathology disclosed follicular adenoma.

Comments.

1. The cytological differential diagnostic includes hyperplastic nodule, follicular adenoma, follicular carcinoma and follicular variant of papillary carcinoma in this order with decreasing likelihood.

2. The ultrasound pattern was suspicious because of the irregular shape and the taller-than-wide sign but made a follicular tumor unlikely because of the lack of halo signs and perinodular blood flow.

3. The results of both the PET-CT and the MIBI were also misleading.