Breast sebaceous cyst

Breast sebaceous cyst, also sometimes known as an epidermal inclusion cyst or simply epidermoid cyst, is a benign breast lesion (BIRADS II). 

For a general discussion of this entity outside the breast, please refer to epidermal inclusion cysts. 

Terminology

The two terms, breast sebaceous cyst and epidermal inclusion cyst, are not entirely synonymous as a sebaceous cyst has an epithelial lining as opposed to a epidermal inclusion cyst, which has an epidermal lining. As far as imaging is concerned, the two entities are indistinguishable from each other ⁶.

The sebaceous cyst implies that the lesion originates in the sebaceous glands, which is not the case and thus the term should be avoided. The epidermal inclusion cyst refers to an epidermoid cyst due to implantation of epidermal elements in the dermis. The preferred term is usually an epidermoid cyst. However, in reality, the terms are used interchangeably.

Pathology

A sebaceous cyst originates in the sebaceous gland while an epidermoid cyst, which is used interchangeably with the previous term, has its origin in the follicular infundibulum.

Location

These lesions are typically located in the skin or subcutaneous tissue. There may be a predilection towards the inframammary fold.

Radiographic features

Mammography 

They are usually seen as well-circumscribed rounded soft tissue density lesions close to the skin surface. 

Breast ultrasound

They may be often seen as small and hypoechoic and again located close to the skin surface with through transmission and with no detectable vascular flow. Hypo- and hyperechoic alternating rings may sometimes be seen on sonography. In some occasions, a characteristic track may be seen extending into the skin surface.

Doppler imaging on ultrasound may on occasion show quite remarkable "flow". Possible low grade infection is not excluded.

Treatment and prognosis

When inflammation is present - both clinical and as well as imaging follow up is advised ⁷.

Complications

• infection: inflammation
• cyst rupture causing a foreign-body or granulomatous reaction, or abscess formation
• malignant transformation into a low-grade squamous cell carcinoma is extremely rare but has been reported

Differential diagnosis

Considerations on mammography include:

• accessory nipple ⁵: particularly if along the milk line on breast tissue 

On ultrasound also consider:

• Montgomery tubercle: particulary if it is at the nipple-areolar region