Epidermal inclusion cysts are common cutaneous benign inflammatory lesions, and have been found in various parts of the body that are usually located in the face, scalp, neck, and trunk. Only a few cases of epidermal cysts of the breast have been reported in the literature and most of these cases are small in size except 1 case where the reported size was 9 × 8 cm [2
]. Furthermore, a larger than 7 cm large size epidermal inclusion cyst in the breast has not been reported in Korean literature.
Epidermal inclusion cysts have been referred to by various terms including: follicular infundibular cysts, epidermal cysts, and epidermoid cysts. The term epidermal inclusion cyst refers specifically to an epidermoid cyst that is the result of the implantation of epidermal elements in the dermis.
There is no definitive understanding of how epidermal inclusion cysts actually develop, however a few theories of their etiology have been postulated.
Firstly, epidermal inclusion cysts can be congenital, arising from cell nests remaining from cells such as the embryonal mammary ridge. Secondly, they can develop from obstructed hair follicles [1
]. Thirdly, epidermal inclusion cysts may result from trauma, such as reduction mammoplasty or needle biopsy of the breast. These procedures may cause epidermal fragments to be implanted more deeply within the breast tissue and a concurrent stimulation of epithelial proliferation [3
]. Fourthly, pilosebaceous structures may become inflamed, leading to a cystic reaction in the dermis. This theory is typically used to explain the presence of cysts on the face, neck, and trunk [4
]. Finally, epidermal inclusion cysts may be created by squamous metaplasia of normal columnar cells within a dilated duct in the case of fibrocystic disease or in a fibroadenoma or phyllodes tumours [5
Most breast epidermal inclusion cysts occur in the skin layer and physical examination revealed a firm, well described, and small mass.
The mammography appearance of epidermal inclusion cyst in the breast typically appears to be well circumscribed with homogeneous increased density. The sonographic appearance of epidermal inclusion cyst in breast may have a solid, well-circumscribed and complex or heterogeneous appearance. Some reports described the specific sonographic features of these lesions such as an onion ring appearance with alternating concentric hyperechoic and hypoechoic rings containing lamellated keratin, while other reports described cysts with extension into the dermis [6
]. Magnetic resonance imaging analysis of epidermal inclusion cysts showed a fluid-like signal with variable low-signal components on T2-weighted images and peripheral rim enhancement on gadolinium-enhanced images [7
An epidermal inclusion cyst of the breast can result in several problems even if the size is unusual. First, spontaneous rupture of the large epidermal inclusion cyst may occur releasing nonabsorbable keratin that acts as an irritant leading to secondary foreign body reactions, granulomatous reactions or abscess formation [2
]. More over, an association between epidermal inclusion cyst and squamous cell carcinoma has been reported. But incidence of malignant potential is extremely variable (0.045 to 19%) and true incidence is uncertain. Finally, a large sized cyst in the breast parenchyma should be evaluated using the differential diagnosis of a large fibroadenoma or phyllodes tumor, or even as a malignant breast lesion with benign features such as mucinous carcinoma [8
Asymptomatic small sized lesions do not require treatment. Furthermore, biopsy is unnecessary if typical sonographic, mammographic, and clinical findings are found. However, epidermal inclusion cysts, especially palpable breast masses in women and large sized lesions that may cause patient discomfort physically and psychologically, require surgical excision. Entire cyst wall removal is recommended for both pathologic confirmation, such as a malignant lesion with benign imaging findings, and for the prevention of potential risks of recurrence (about 3%), inflammation, and malignant change [10