Ultrasonographic findings in relation to ease of aspiration and fluid characteristics in thyroid cyst.

Sixty-six thyroid cysts in 65 patients were studied prospectively using the aspiration method and ultrasonography. The major post-aspiration ultrasonographic change was thyroid tissue enlargement in 95% (62/65) in addition to the decreased size of the thyroid cysts in all. More than double increments of thyroid tissue could be noted in 54% (35/65) of the patients. The color of cystic fluid was related to the duration of the cyst and internal echogenicity (p less than 0.01 and p less than 0.02, respectively). Acute hemorrhage usually had a dark-reddish fluid and an increased echogenicity. The viscosity of the cystic fluid could influence the success rate of aspiration (p less than 0.05). The effect of aspiration was not good if the thyroid cyst had thick gelatinous fluid. Because a cystic goiter may be associated with malignancy, aspiration biopsy should be performed after the fluid is drawn especially if the thyroid tissue is expanded. If there is no evidence of malignancy, aspiration can be tried more than once if the cyst reappears.