Clinical presentation: A 32-yr-old woman requested a second opinion. She was at the 31st gestational week. She has been treated with levothyroxine since the early weeks of pregnancy because of a TSH level (3.41 mIU/L) which was held not ideal.

Palpation: no abnormality.

Laboratory tests: TSH 0.04 mIU/L, FT4 17.6 pM/L, aTPO undetectable on daily 75 microgram levothyroxine.

Ultrasonography. The thyroid was echonormal. There was a cystic lesion in the lower pole of the left lobe. The nodule was almost completely cystic, however, tiny echonormal portions were found in several locations at the cyst wall.

Three mL yellow fluid was aspirated. There were numerous macrophages and scattered number of follicular cells on the smear. Cytology resulted in benign cystic lesion, more likely of thyroidal and not of parathyroid origin.

Wash out thyroglobulin> 486 ug/L, while wash-out parathormone was 0.5 ng/mL - both stood for a thyroid lesion.

Suggestion. Discontinuation of replacement therapy. Repeat TSH in six months, repeat ultrasound in a year.

Comments.

1. The ideal TSH differs from the normal values in the event of an underlying Hashimoto's thyroiditis. In such cases a TSH exceeding 3 mIU/L might be an indication of replacement therapy in childbearing age. However, in woman who does not present any signs of autoimmune thyroiditis, i.e. neither the aTPO nor the ultrasound suggests thyroiditis, there is no indication of replacement therapy if the TSH is within the normal range.

2. The nodule did not meet the criteria of a purely cystic nodule before the aspiration because there were solid-looking tiny areas within. However, the lesion completely disappeared during the aspiration. It means that this was a pure cystic nodule. (Solid fragments cannot be removed with a 23G needle.) This case illustrates why can frequently define the type of a cyst exactly only after the aspiration of the cystic content.

3. Although the location of the cyst favored a parathyroid origin, wash-out hormone determinations proved that the cyst was of thyroidal origin.

4. The nodule is an Eu-TIRADS 2 lesion.