Sonographic features of mammary oil cysts

Mammographic lesions that are pathognomonic for oil cysts require no further evaluation. Oil cysts, however, may first be discovered by ultrasonography. Between 1988 and 1995, we performed sonography of 26 oil cysts in 15 patients. Sonography was used to evaluate a palpable finding when an oil cyst was not initially perceived on the mammogram (47%) or as an initial evaluation of a palpable lump (33%); in addition, oil cysts were identified incidentally in 20% of cases. Retrospective review showed that the sonographic appearance of oil cysts is highly variable; only 8% mimic simple apocrine cysts. Twelve percent mimic an intracystic mass. Most have smooth walls (88%), are hypoechoic (65%), and have neither enhancement or shadowing (50%). The sonographic appearance of oil cysts can be suggestive of a pathologic lesion such as an intracystic carcinoma. Unnecessary biopsy can be avoided using directed mammography.