Cysts

Gross cysts (palpable fluid-filled macrocysts) are the most common lumps found in the breast. Cysts vary tremendously in size and number and may be microscopic or macroscopic. Their rate of development also varies significantly; cysts may develop almost overnight or more gradually and may resolve as rapidly.

Cysts may occur in patients as young as 25 years but are most common in women between the ages of 35 and 50 years. The development of breast cysts usually ceases with menopause; occasionally, however, these tumors occur in a postmenopausal patient-particularly if she has been receiving estrogen replacement therapy.

Breast cysts appear to originate from the terminal duct-lobular unit, primarily through hormonally regulated dilatation and failure to shrink after menstruation, or they may arise from an obstructed duct. The epithelium of these cells is usually two-layered, as seen in normal breast ducts and lobules. The stroma surrounding these cysts is variably fibrotic and often shows clusters of chronic inflammatory cells.

Clinically, gross cysts may be silent or painful. Some may cause palpable lumps, while others may be visible only on ultrasound. The presenting symptom of a rapidly developing cyst is often localized pain, thought to result from the distention of the surrounding tissue or possibly from a sterile inflammatory reaction caused by the escape of cystic fluid into the surrounding breast tissue.

The consistency of these cysts depends on the pressure of fluid within them and the amount of normal breast tissue surrounding them. If the fluid pressure is low, they will appear soft and fluctuant; however, tense or deep cysts may feel like solid tumors. These cysts are often solitary but may be multiple, feeling somewhat like a cluster of grapes on palpation.

Mammography may reveal smooth-walled masses that ultrasound shows to be benign cysts. Such cysts do not require aspiration unless the patient feels tenderness or unless atypical sonographic features are present.

Ultrasound-guided fine-needle aspiration is appropriate for both diagnosis and treatment of more complex cysts, such as those with internal echoes, thick internal septa, thick walls, or mural nodules. It is also useful to clarify indeterminate mammographic findings.

The relationship of gross cysts to cancer has been controversial. There appears to be an increased incidence of breast cancer in those women with gross cysts who have a family history of premenopausal breast cancer among first-degree relatives (mother, sister, or daughter) but no significantly increased risk among those without any such family history.