Breast cysts commonly occur in the fifth and sixth decades, with a peak incidence occurring around the age of 50. It can therefore be assumed that their etiology is related to an alteration in the overall hormonal profile of the patient. Cysts can be single or multiple and may be symptomatic or detected on mammographic screening.

Cysts can appear suddenly, grow to any size and may be associated with pain and tenderness. They may be single or multiple, unilateral or bilateral.

Cysts often appear as well-circumscribed, discrete, mobile lesions that may be fluctuant if they lie superficially in the breast. Alternatively, they may be much firmer if they are tense.

Cysts appear as well-defined soft-tissue densities. They may exhibit the “halo sign”; however, it rarely encircles the lesion completely. This is due to the fact that cysts are often obscured by surrounding breast tissue.

Simple cysts are frequently multiple and bilateral and are seen against a background of dense breast tissue. Calcification in the wall of a cyst (rim calcification) is uncommon and usually follows needle aspiration.

Ultrasound is the mainstay of diagnosis and is extremely reliable in distinguishing solid from cystic masses. Cysts appear as well-defined, anechoic, thin-walled lesions. As sound travels through liquid with little attenuation, the tissue deep to a cyst appears bright (posterior enhancement). Mural lesions such as intracystic papillomas, which are only very occasionally seen, can be easily visualized using ultrasound. Some simple cysts contain inspissated material, which can make a cyst appear solid. If there is any diagnostic doubt as to whether a lesion is cystic or solid, ultrasound-guided aspiration/needle biopsy should be performed.

Macroscopic Appearance
Cysts range in size from a few millimeters to several centimeters in diameter. They are often multiple and may be bilateral. The cyst wall may be smooth, thin and glistening or thickened and fibrotic due to the presence of granulation tissue and inflammation invoked by previous rupture. The cyst contents may be thin, straw-colored fluid or thick green-to-brown material, indicating the presence of inflammatory cells or altered blood within the cyst fluid.

Microscopic Appearance
The cyst lining is usually composed of flattened ductal epithelial cells or apocrine metaplastic epithelium that may show papillary projections. Foamy macrophages are frequently present in the cyst lumen and may also be seen infiltrating the lining epithelium if it is ductal in type.

If the cyst wall is thickened macroscopically, the lining is usually composed of granulation or laminated fibrous tissue with varying amounts of inflammatory cells. Trapped epithelial structures are often seen in thickened cyst walls.

Aspiration of the cyst to dryness is the treatment of choice. Normally, the cyst fluid is discarded. If the fluid is uniformly blood stained, it should be sent for cytology. Following aspiration of a cyst, the patient should be reexamined, and the clinician should confirm that the previously palpable lump has disappeared. Any residual areas of nodularity should be investigated similarly to any other discrete lump (i.e., FNAB or core biopsy). Recurrent cysts are aspirated as and when they cause symptoms. There is no place for surgical excision.

Cysts and Risk of Breast Cancer
The relationship between cysts and breast cancer risk is controversial.

Based on the potassium:sodium ratio, cysts have been classified into type 1 (apocrine/secretory), type 2 (attenuated/flattened) and mixed cysts (type 1 cysts ratio >1.5; type 2 cysts ratio <1.5).

In a large study involving 802 patients with a median follow-up of six years,  the incidence of breast cancer in type 1 cysts has been shown to be greater than in type 2 or mixed cysts (RR 4.62). It is not routine practice to analyze aspirated cyst fluid for its electrolyte content. Other studies have demonstrated that, irrespective of cyst type, there is an increased risk of developing breast carcinoma in all women (RR 1.7).

A.D. Purushotham, P. Britton and L. Bobrow
A prospective study of benign breast disease and the risk of breast cancer. JAMA 2002


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