Breast filariasis: real-time sonographic imaging of the filarial dance.

A 50-year-old woman presented with a palpable tender nodule in the upper quadrant of the breast that was clinically thought to be a fibroadenoma, with mammographic findings of a well-defined lobulated density. Sonographic examination revealed a "filarial dance sign" within the cystic lesion, which is diagnostic of lymphatic breast filariasis. In endemic areas, sonographic examination is recommended to search for this pathognomonic real-time diagnostic feature and, if present, to initiate treatment without delay.