BACKGROUND: Epidermal inclusion cysts rarely develop in the breast. The cysts that do develop within the breast typically present as cutaneous or subcutaneous cysts. They more rarely present in a subareolar location or in a ruptured state. Thus far, 5 cases of ruptured epidermal inclusion cysts in subareolar locations have been reported in the English literature. Furthermore, clinical presentation of nipple discharge is rare in epidermal inclusion cysts of the breast; only 4 such cases has been reported.

CASE REPORT: A 58-year-old female presented with a 1-month history of bloody discharge from her left nipple. Mammography showed focal asymmetry in the left subareolar region; sonography showed a left subareolar mass with irregular shape, indistinct margin, heterogeneous echogenicity, and posterior enhancement. The mass was surgically excised; a pathological diagnosis of ruptured epidermal inclusion cyst with foreign body reaction and abscess formation was established. In this case, the clinical presentation of bloody nipple discharge was peculiar; furthermore, mammographic and sonographic features were indistinguishable from breast malignancy or typical breast abscess.

CONCLUSIONS: A ruptured epidermal inclusion cyst can present in an unusual subareolar location, combined with bloody nipple discharge; importantly, this can radiologically resemble breast malignancy.

Keywords: Breast, Epidermal Inclusion Cyst, Mammography, Ultrasonography, Mammary, Biopsy, Needle, Breast Diseases, Breast Neoplasms, Diagnosis, Differential, Epidermal Cyst, Foreign-Body Reaction, Immunohistochemistry, Nipples, Rare Diseases, Risk Assessment, Rupture, Spontaneous, Ultrasonography, Doppler, Color