Differentiating a cyst from a solid lesion of the breast by ultrasonography may be difficult, especially if the cyst contains mildly echogenic proteinaceous debris. Routine cytologic examination of fluid from breast cysts is recommended by some authorities, while others believe it is not useful. Most authors, however, advocate cytologic analysis if the fluid is bloody. Previous studies of the utility of cytologic analysis of fluid from breast cysts have been performed in women with palpable breast masses. Smith and associates studied the utility of cytologic examination of fluid from nonpalpable breast masses with the sonographic appearance of simple cysts.

The results of cytologic examination in 583 women (660 nonpalpable breast cysts) evaluated over 42 months were retrospectively reviewed. The fluid was obtained by sonographically or mammographically guided needle aspiration.

No malignant cells were seen on cytologic examination of fluid from 541 cysts (82 percent of the cysts). Insufficient material was obtained from 86 cysts (13 percent of the cysts). In 33 cysts (5 percent), atypical cells were identified on cytologic examination. Surgical biopsy was performed in nine of these patients; histology revealed fibrocystic changes in eight patients and intraductal papilloma in one patient. The remaining 24 patients received periodic follow-up examinations, and all of the lesions appeared smaller or were not seen during the follow-up examination.

Grossly bloody fluid was obtained from 42 cysts. Three exhibited a dark color, suggesting old blood, but no atypical cells were noted on cytologic examination. Of the remaining 39 cysts with bloody fluid, five showed atypical cells on cytologic examination. Four of these five patients underwent biopsy, and all results were benign.

The authors conclude that if the fluid obtained from radiologically guided aspiration of nonpalpable breast cysts is not bloody, routine cytologic examination is not necessary unless other radiologic findings suggest malignancy. The authors recommend that grossly bloody fluid be sent for cytologic analysis, although the yield appears to be low.