Clinical data: A 33-year-old man was referred for evaluation of a mass in the right thyroid. The patient suffered a neck trauma when boxing 5 days before the present examination. He noticed an increasing mass in the location of the right thyroid within hours after the trauma.

Palpation: The right lobe was composed of a large elastic nodule.

Functional state: subclinical hyperthyroidism with TSH 2.57 mIU/L.

Ultrasonography: The thyroids were echonormal. A large cystic nodule composed of multiple chambers occupied almost the entire right lobe with the breakage of the fibrotic bundles dividing the chambers of the cyst. The nodule presented halo sign and perinodular blood flow.

We aspirated 23 mL bloody fluid but the size of the nodule remained unchanged because the cyst refilled at once during the process of evacuation.

Surgery was advised.

Histopathology disclosed benign cystadenoma of the right lobe.