Clinical data: A 73-year-old man was referred for evaluation of a thyroid cyst which was discovered on chest X-ray by chance. The patient had no complaints.

Palpation: no abnormality.

Laboratory tests: TSH 3.21 mIU/L, aTPO < 28 U/mL.

Ultrasonography. The thyroid was echonormal. There was a large cyst under the lower pole of the left lobe. This was an almost complete cyst.

18 mL watery fluid was aspirated. There were no cells on the smear.

Additional tests: serum-parathormone 31.6 pg/mL (normal value 12-88), parathormone content of the aspirated fluid 175 pg/mL.

Suggestion: ultrasound in a year or two.