Dirofilariasis of breast: report of two cases diagnosed by fine-needle aspiration biopsy.

We report on 2 cases of dirofilariasis of the breast occurring in adult Chinese females residing in Hong Kong. The diagnosis was made by fine-needle aspiration biopsies. The direct smears contained numerous acute inflammatory cells, including eosinophils. A partially necrotic adult nematode of about 400-450 microm in diameter was identified in the cell-block sections of each case. The worm was characterized by a thick cuticle with longitudinal cuticular ridges and fine transverse surface striations, abundant somatic muscle, an intestine, and a reproductive tube or uterus. The morphologic features of this round worm were most compatible with those of Dirofilaria repens. While the clinical and radiologic findings of dirofilariasis of the breast are nonspecific and mimic those of breast neoplasms or inflammatory conditions, a definitive diagnosis is possible with fine-needle aspiration biopsy. A correct diagnosis of dirofilariasis may help to spare patients from unnecessary medical and surgical interventions.