Clinical presentation: A 41-year-old woman came to follow-up investigation. She underwent a left subtotal thyroidectomy at the age of 18 while a near total right lobectomy at the age of 33. Histopathology revealed hyperplastic nodules at both occasions. First, we met the patient before the second operation. At this time the dimensions of the previously resected left lobe were 12x12x30 mm (width, depth, length, respectively) and had a moderately hypoechogenic lesion with a maximal diameter of 8 mm which has gradually increased over the last ten years. 6 weeks before the present examination the patient noticed a sudden increase in the size of the left lobe.

Palpation: There was an elastic nodule in the left lobe.

Result of blood test: TSH 0.89 mIU/L.

Ultrasonography. The right lobe was decreased in size and had two hypoechogenic small areas. There was an almost pure cyst in the right lobe with the dimensions of 26x20x33 mm, width, depth, length, respectively. The lesion had numerous comet-tail artifacts.

7.5 mL brown cystic fluid was aspirated. Cytology resulted in benign lesion.

Suggestion: ultrasound in a year, in the event of complaints at once. Sclerotherapy if the nodule will refill.

Comment. The type of the cyst is difficult to determine. Considering the presentation during and after the aspiration, it is a bit more likely that the cyst belongs to the peripheral-type subgroup.