To classify the ultrasonographic findings of cystic lesions of the breast and correlated them with the pathology, to evaluate the characteristic features of cystic masses in benign and malignant tumors, and to determine the appropriate level of patient management according to the ultrasonographic findings.

From June 2002 through to June 2004, the ultrasonographic findings of 113 pathological proven cystic breast lesions were reviewed retrospectively. The cystic lesions were classified as simple acysts, clustered cysts, cysts with thin septa, complicated cysts, cystic masses with a thick wall/ septa or nodules, and complex solid and cystic masses. The ultrasonographic findings of each type of cystic lesion of the breast were compared with the pathology and evaluated according to whether they were benign or malignant.

Of the 113 lesions, there were 17 simple cysts, 10 clustered cysts and 19 cysts with thin septa. Twenty four cases of complicated cysts were found to be benign. Five (31.3%) of the 16 cases of cystic masses with a thick wall / septa or nodules and 17 (63%) of the 27 cases of complex solid and cystic masses were found to be malignant. The shape and margin of the 43 cases of cystic masses with a solid component were analyzed. Seventeen out of 36 sonographical round or oval shaped masses and 10 out of 27 sonographical circumscribed margins were found to be malignant.

The simple cysts, clustered cysts, cyst with thin septa and non-symptomatic complicated cysts detected by sonography were all benign. Symptomatic complicated cysts should be aspirated and treated appropriately. Cystic masses with a solid component should be examined by a biopsy with a pathological confirmation.