A 36-year-old woman presented with a palpable right breast mass that had slowly enlarged over the course of 12 years. Diagnostic mammogram demonstrated an oval, circumscribed mass in the right upper central breast at mid-depth, corresponding to the palpable area of concern (Figure 1). No additional significant findings were detected in either breast.
Diagnostic mammogram images of a 36-year-old woman with epidermoid cyst. Craniocaudal (A) and mediolateral oblique (B) 2D views of the right breast demonstrate an oval bilobed circumscribed equal density mass in the upper central right breast corresponding to the palpable mass. The triangle marker denotes the palpable mass.
US evaluation of the palpable mass in the right breast demonstrated a 3.8-cm predominantly hypoechoic, mildly heterogeneous, oval circumscribed mass without internal vascularity in the superficial tissue (Figure 2).
US images of a 36-year-old woman with an epidermoid cyst. Right breast grayscale (A) and power Doppler (B) images demonstrate an oval heterogeneous and circumscribed parallel mass with posterior acoustic enhancement and no detectable internal blood flow. There was no tract visible to the skin surface.
Given its slow growth over the course of 12 years, this was categorized as a Breast Imaging Reporting and Data System (BI-RADS) 4A lesion with low suspicion for malignancy. Subsequent US-guided biopsy results demonstrated keratinous debris consistent with the contents of an epidermoid cyst (EC) (Figure 3).
(A) US-guided core needle biopsy of the mass using a 14-gauge spring-loaded core device. (B) Postbiopsy mammogram confirms the presence of a ribbon-shaped biopsy marker within the mass.
An EC is a common benign skin-related mass that occurs in the skin or subcutaneous tissue and is contained within epithelium. In hair-bearing areas of the body, an EC may develop in the upper portion of a hair follicle because of occlusion of the pilosebaceous unit. In other areas of the body, ECs may be due to proliferation and implantation of epidermal elements within a circumscribed space. An EC is typically filled with lamellated keratin. Epidermoid cysts are commonly misdescribed as sebaceous cysts, which are far less common and arise from the sebaceous glands.
Epidermoid cysts occur anywhere within the body but most commonly involve the scalp, head and neck region, trunk, and extremities. Multiple theories regarding the pathogenesis behind ECs of the breast have been posited. These include a prior history of trauma or surgery that leads to damage of the epidermis, congenital origin from specific cells from the embryonic mammary ridge, and ectasia and obstruction of the infundibulum of hair follicles as well as metaplasia of normal columnar cells.
On mammography, ECs are typically seen as circumscribed equal density masses close to the skin surface. On US, these masses are typically seen as hypoechoic without detectable vascular flow. On some occasions, a track extending to the skin surface may be observed and is pathognomonic for the diagnosis of EC.
The differential diagnosis for this finding includes other superficial lesions of the breast. If close to the nipple areolar complex, a lesion could be a Montgomery’s tubercle cyst. Infrequently, it may be a sebaceous cyst. Solid masses such as fibroadenoma, phyllodes tumor, or, rarely, a well-circumscribed breast cancer are also included in the differential. In cases in which the mass is partially contained within the skin surface, the growth size is minimal, or a tract through the skin is visible, further workup may not be required. If the mass remains a diagnostic dilemma, a biopsy may be necessary, as in the case presented.
There are potential complications associated with these masses, including infection, cyst rupture resulting in foreign body/granulomatous reaction, or, very rarely, malignant transformation into a low-grade squamous cell carcinoma.
Epidermoid cysts can be managed in a variety of ways, depending on their presentation. Treatment is not required for asymptomatic lesions. However, palpable or enlarging masses may require follow-up or a biopsy. If removal is desired, treatment typically involves surgical excision of the EC and its capsule.
Conflict of interest statement
None declared.
