Clinical data: A 42-year-old woman was referred for evaluation of a suspicious mass which was found on ultrasound examination. Six months ago, breast cancer was diagnosed. The neck ultrasound was part of the follow-up. Otherwise, the patient has been treated for hypothyroidism for more than 10 years.

Palpation: a firm lesion in the middle of the neck above the usual location of the thyroid.

Functional state: subclinical hyperthyroidism with TSH 5.09 mIU/L, FT4 13.6 pM/L, aTPO > 1300 U/mL, ahTG > 500 U/L.

Ultrasonography. The thyroid was deeply hypoechoic and presented fibrosis. There were no pathological nodules within. Approximately 3 cm above the upper level of the thyroid, a hypoechoic mass was found. Th echogenicity of this mass was similar to that of the thyroid. .

Cytology was performed from the lesion above the thyroid and resulted in Hashimoto's thyroiditis.

Suggestion: to increase the replacement dose to daily 125 microgram. Ultrasound in two years.

Comment. The location of the mass corresponded to the lobus pyramidale, however, there was no connection between the mass and the thyroid. Therefore, this lesion should be considered as an aberrant thyroid.