Clinical data: A 59-year-old man was referred for regular follow-up examination. He was operated because of a diffuse goiter causing compression signs 16 years ago. Histopathology revealed Hashimoto's thyroiditis. For several months he has noticed a slowly growing submental mass. One year before present investigation no abnormalities were found in the region of the neck.

Palpation: a firm, painless mass in the submental region.

Laboratory test: euthyroidism on daily 75 microgram levothyroxine (TSH 4.56 mIU/L).

Ultrasonography. There were small hypoechogenic areas surrounded with an echonormal rim in the thyroid beds. A cystic lesion was detected in the submental region. The mass had irregular borders and presented signs of intralesional vascular pattern.

Aspiration cytology was performed and a minimal amount of brown fluid was aspirated. Cytological diagnosis: suspicion of thyroid papillary carcinoma.

Wash-out thyroglobulin level was above 476 ng/mL, serum-thyroglobulin was 3.01 ng/mL, serum anti-hTg was 70.6 U/mL.

Histopathology disclosed thyroglossal duct cyst.

Comment. It is impossible to make distinction between a thyroglossal duct cyst and a cystically degenerated ectopic thyroid tissue on ultrasound.