Effects of fine-needle aspiration on the US appearance of the breast.

Fine-needle aspiration (FNA) of normal breast tissue or benign lesions can cause changes that suggest malignancy at ultrasound (US) examination. Serial US studies showed that three of 17 patients developed signs mimicking malignancy following FNA of palpable breast lumps. A second group of 14 patients had US signs of malignancy in palpable lumps following recent FNA. Nine patients with benign lesions were unnecessarily worried, since the appearance was probably due to FNA. Diagnosis of malignancy was delayed in one of five patients because the US appearance was attributed to the FNA in the presence of false-negative cytologic findings. FNA of normal breast tissue or benign masses produced tissue changes in 18% of cases that altered the US appearance from normal or benign to possibly malignant. The changes took up to 4 months to subside. If US is clinically indicated, it should be performed before FNA.