Breast cysts: Clinical manifestations, diagnosis, and management

INTRODUCTION — A breast cyst is a fluid-filled round or ovoid mass derived from the terminal duct lobular unit (TDLU) (image 1). Cysts begin as fluid accumulation in the TDLU because of distension and obstruction of the efferent ductule [1]. (See "Breast development and morphology", section on 'Lobule formation'.)

Breast cysts, which can present as a solitary mass or as multiple masses, usually prompt women to seek medical attention because of the palpable mass or associated pain or discomfort. A breast cyst may be first identified on a clinical or self-breast examination or as a mammographic mass or density. Breast cysts may fluctuate in size, number, and magnitude of symptoms.

The clinical features, diagnosis, and management of breast cysts are the focuses of this topic. Information on evaluation and treatment of solid breast masses, both benign and cancerous, can be found in other UpToDate topics:

●(See "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass".)

●(See "Diagnostic evaluation of suspected breast cancer".)

●(See "Clinical features, diagnosis, and staging of newly diagnosed breast cancer".)

●(See "Overview of the treatment of newly diagnosed, invasive, non-metastatic breast cancer".)

EPIDEMIOLOGY — Breast cysts are common masses found in premenopausal, perimenopausal, and postmenopausal women. In a prospective study of 2809 women at increased risk of breast cancer development, the American College of Radiology Imaging Network (ACRIN) 6666 protocol found that cysts were identified in 37.5 percent of all women screened, with the peak incidence between 35 and 50 years of age [2]. During this three-year screening study, cysts were identified more often in premenopausal women compared with postmenopausal women (65.1 versus 39.4 percent). Hormone replacement therapy (HRT) was used by 5.4 percent (n = 73) of postmenopausal women, and 66 percent of HRT users were diagnosed with cysts.

Symptomatic and asymptomatic small cysts (microcysts) are common in young premenopausal women [3]. Breast cysts are influenced by hormonal function and fluctuation. Therefore, they occur during lobular development, menstrual cyclic changes, and lobular involution in premenopausal and perimenopausal women [4]. (See "Overview of benign breast diseases", section on 'Nonproliferative lesions' and "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass", section on 'Benign'.)

The natural history of breast cysts consists of cyclic development and regression; 69 percent resolve within five years [5].

CLINICAL FEATURES

Patient presentation — A breast cyst can present as a painful or painless, often solitary, mass. The mass may be large (gross), small (microcysts), or a cluster of small microcysts. (See "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass", section on 'Presenting symptoms'.)

Acute enlargement of cysts may cause severe, localized pain of sudden onset. Microcystic changes of the breast frequently cause pain and/or tenderness prior to the onset of menses, and sometimes pain persists throughout the menstrual cycle. (See "Breast pain", section on 'Cyclical breast pain'.)

Physical examination findings — Physical examination alone cannot definitively distinguish between a benign cyst, benign solid mass, and malignancy. A large or small breast cyst can be palpated as a smooth, firm, discrete, and frequently tender mass. Cysts may present as a cluster of small masses or as an ill-defined mass. The texture is variable, often described as similar to a grape, water balloon, or even hard mass. Some, but not all, cysts have a sharp distinct border and are ballotable. (See "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass", section on 'Physical examination' and "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass", section on 'Benign'.)

Imaging — Breast cysts can be evaluated by several imaging studies. The choice of the initial breast imaging modality depends on the woman's age, which is discussed elsewhere. (See "Diagnostic evaluation of suspected breast cancer", section on 'Palpable breast mass'.)

Ultrasonography — Ultrasonography is used to differentiate between a mass that is fluid filled, solid, or contains mixed elements.

Classification — Cysts are classified as simple, complicated, or complex based upon the sonographic features (see "Diagnostic evaluation of suspected breast cancer", section on 'Breast ultrasound'):

Simple — A simple cyst is well circumscribed with ultrasonic features that include posterior acoustic enhancement without internal echoes (anechoic), solid components, or Doppler signal (image 2 and image 3). Simple cysts are, by definition, benign lesions.

Clustered microcysts and cysts with thin septa are subsets of simple cysts [6]. Clustered microcysts are a cluster of simple anechoic cysts, each smaller than 2 to 3 mm, without discrete solid components. Cysts with thin septa that are less than 0.5 mm in thickness are defined as simple cysts.

Complicated — Complicated cysts are defined by ultrasound criteria as masses with homogenous low-level internal echoes due to echogenic debris, without solid components, thick walls, or thick septa, and without vascular flow (image 4).

Complex — Complex cysts are defined by ultrasound criteria as masses with thick walls and/or septa greater than 0.5 mm, presence of cystic and solid components, and absence of posterior wall enhancement (image 4) [7]. The ultrasound appearance of complex cysts can demonstrate anechoic and echogenic components.

BI-RADS categories — The Breast Imaging-Reporting and Data System (BI-RADS) final assessment categories used for reporting mammographic findings and recommendations are also applicable to ultrasound examinations [8-11]. Assessments are either incomplete (category 0) or final assessments (categories 1 through 6) (table 1). The BI-RADS assessments are used to guide clinical decision making and the need for biopsy:

●Simple cysts, clusters of simple microcysts, and most complicated cysts are BI-RADS 2 (benign), for which tissue sampling is not warranted. (See 'Simple cyst' below.)

●Occasionally, complicated cysts can be BI-RADS 3 (probably benign), for which short-interval (six-month) follow-up clinical and imaging examinations are indicated. (See 'Complicated cyst' below.)

●Complex cysts should be BI-RADS 4 or 5 (suspicious or highly suggestive of malignancy), for which biopsy is required. (See 'Complex cyst' below.)

Risk of malignancy — There is no increased risk of breast cancer detection in a mass that fulfills the ultrasound diagnostic criteria of a simple cyst [3,12], and breast cancer presenting as a complicated cyst is rare (<1 percent) [2,3,12]. However, the risk of malignancy in a complex cyst generally ranges from <1 to 23 percent [3,13-18]. The wide range of malignant findings may be due, in part, to technical accuracy of ultrasound to differentiate solid from cystic components of breast masses and the interpretation of the ultrasound findings. (See 'Subsequent breast cancer risk' below.)

Ultrasonographic features that increase the likelihood of malignancy in the complex cystic breast mass include thickened cyst walls, thick septations, mixed cystic/solid components, lobulations, indeterminant classifications, and hyperechogenicity [3,14,17,18]. The presence of two or more abnormal ultrasonographic criteria was associated with a 10- to 14-fold increase in breast cancer detected in the lesion [14,17].

Incomplete resolution and/or bloody fluid following ultrasound-guided fine needle aspiration were also associated with malignant findings in a complex cyst [15]. (See 'Complex cyst' below.)

Mammography — Mammography depicts a large cyst (image 5) or a cluster of small cysts (image 6) as a mass or a density that has well-defined or partially obscured borders. Small microcysts typically are not visualized on a mammogram. (See "Breast imaging for cancer screening: Mammography and ultrasonography", section on 'The mammographic examination' and "Diagnostic evaluation of suspected breast cancer", section on 'Mammography and digital breast tomosynthesis'.)

MRI — Magnetic resonance imaging (MRI) depicts a cyst as a round or oval sharply defined mass (image 7). A cluster of cysts is similarly depicted (image 8). The typical cyst will appear with bright, high-signal-intensity on T2-weighted fat-suppressed images. After injection of gadolinium, a cyst appears as a filling defect, sometimes with rim enhancement. If septations are present, they are nonenhancing [19]. In a study evaluating complex cystic breast lesions with MRI, rim enhancement was the dominant pattern in benign lesions [20]. By contrast, malignant lesions were associated with heterogeneous contrast enhancement, type III kinetic curves, diffusion restriction, and tall choline peaks.

Suspicious cystic lesions found incidentally on breast MRI should prompt further evaluation with breast ultrasound. The indications and findings on MRI of the breast are reviewed elsewhere. (See "Diagnostic evaluation of suspected breast cancer", section on 'Breast MRI' and "MRI of the breast and emerging technologies".)

DIAGNOSIS — A breast cyst is suspected by either physical finding of a palpable breast mass or an abnormal imaging finding (most commonly a mammogram). A breast cyst is diagnosed by breast ultrasound. Breast ultrasound also provides information about whether the breast cyst is simple, complicated, or complex; such information dictates further management. (See 'Management' below.)

DIFFERENTIAL DIAGNOSIS — The differential diagnosis of a breast cyst, whether identified on a self- or clinical breast examination or by an imaging study, includes benign and malignant lesions [21-23]. (See "Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass" and "Diagnostic evaluation of suspected breast cancer".)

●A mass that fulfills the ultrasonographic criteria for a simple cyst is a simple cyst. A fine needle aspiration (FNA) that identifies nonbloody fluid and results in complete collapse of the mass is also diagnostic of a simple cyst. No further diagnostic evaluation is required. (See 'Simple cyst' below.)

●The differential diagnosis of a complicated or complex cyst includes:

•Abscess – A breast abscess presents with localized, painful inflammation of the breast associated with fever and malaise, along with a fluctuant, tender, palpable mass. Although this is primarily a clinical diagnosis, ultrasound imaging is helpful for confirmation of the diagnosis and for directed aspiration of the purulent fluid. (See "Primary breast abscess", section on 'Clinical features and diagnosis'.)

•Hematoma – Hematoma is a collection of partially solidified blood that results from trauma or a prior surgical procedure of the breast. An ultrasound may reveal a complicated cystic lesion that may require an aspiration for confirmation.

•Fat necrosis – Fat necrosis of the breast is a benign condition that most commonly occurs as the result of breast trauma or surgery and can be confused with a malignancy on physical examination. It may contain partially liquified fat on the ultrasound assessment. Mammography may show a calcified rim classic for fat necrosis. The diagnosis can be confirmed by a diagnostic needle biopsy. (See "Overview of benign breast diseases", section on 'Fat necrosis'.)

•Galactocele – Galactoceles (milk retention cysts) are cystic collections of fluid, usually caused by an obstructed milk duct. These present as soft cystic masses on physical exam but are not tender and are not associated with systemic findings. Ultrasound may show a complex mass. The diagnosis can be made on the basis of the clinical history and aspiration, which yields a milky substance. (See "Common problems of breastfeeding and weaning".)

•Noninfectious disorder – Noninfectious disorders, including duct ectasia characterized by distension of subareolar ducts with fibrosis, benign inflammatory periductal mastitis, and a ruptured cyst or duct, may present as a complex or complicated cyst on ultrasound imaging. (See "Nonlactational mastitis in adults", section on 'Periductal mastitis'.)

•Oil cyst (image 9) – An oil cyst contains a collection of liquified fat. If there is any question on the ultrasound, an aspiration can be performed to confirm the diagnosis. (See "Overview of benign breast diseases", section on 'Fat necrosis'.)

•Malignancy – A colloidal breast cancer or a cyst wall cancer may have a similar appearance to a complicated or complex cyst on ultrasound, mammography, and/or magnetic resonance imaging (MRI). Apocrine papillary carcinoma can present as a complex cyst with a mural nodule on ultrasound [24,25]. The diagnosis can be established by a diagnostic needle biopsy (preferred) or excisional biopsy. (See "Diagnostic evaluation of suspected breast cancer".)

MANAGEMENT — Once a breast mass is identified as a cyst by breast ultrasound, further management depends upon the clinical presentation of the patient and the imaging characteristics and Breast Imaging-Reporting and Data System (BI-RADS) classification of the lesion (algorithm 1).

Generally speaking, simple cysts, clusters of simple microcysts, and most complicated cysts are BI-RADS 2 (benign), which does not warrant tissue diagnosis. Occasionally, complicated cysts can be BI-RADS 3 and thus should undergo short-interval repeat physical examination and imaging in six months. Complex cysts are BI-RADS 4 or 5 and should undergo ultrasound-guided core needle biopsy (CNB).

Simple cyst — A simple cyst is benign, and no further intervention is necessary [26-28]. Clustered simple microcysts are also benign, and no further intervention is required.

We do not excise simple cysts for any reason. Fine needle aspiration (FNA) of a simple cyst is only performed for signs of infection or inflammation (red skin). In such cases, FNA must be performed under real-time ultrasonographic guidance to assure complete collapse of the cyst [29]. If the aspirated fluid is turbid, it should be sent for culture, but not cytology, as cyst fluid will almost always contain atypical cells. Only frankly bloody fluid should be sent for both culture and cytology. (See "Breast biopsy", section on 'Cyst aspiration'.)

Following FNA of a cyst that completely disappears, no further management is required if there is concordance between the clinical examination and the ultrasound results [30]. The patient can then resume routine annual screening [16]. (See "Screening for breast cancer: Strategies and recommendations".)

If the aspirated cyst does not completely collapse, the procedure can be converted to an ultrasound-guided CNB to obtain a tissue diagnosis. Alternatively, if the FNA is done by palpation alone or by ultrasound not performed by a radiologist, the best practice would be to stop and get a diagnostic mammogram and diagnostic ultrasound first, before pursuing a CNB.

Complicated cyst — Most complicated cysts are BI-RADS 2, which does not require any further intervention. Occasionally, complicated cysts can be BI-RADS 3. Complicated cysts classified as BI-RADS 3 should undergo repeat ultrasound imaging and mammography (if the lesion was visualized on mammography) and clinical examination in six months [12]:

●Worrisome changes (eg, increase in size, development of a solid component) should be pursued by an image-guided CNB. (See "Screening for breast cancer: Strategies and recommendations" and "Breast biopsy".)

●If the complicated cyst is downgraded to BI-RADS 2 on repeat imaging, the woman should undergo clinical examination and imaging (ultrasound and mammography) in another six months. As long as the latest imaging does not classify the lesion as BI-RADS 3 or above, the patient does not require any further intervention and can return to routine annual screening.

●If the complicated cyst remains BI-RADS 3 on repeat imaging, repeat clinical examination and imaging should be continued every six months.

This option does require patient compliance. One study showed that 36 percent of patients who were recommended to have short-term follow-up of cystic lesions did not achieve two years of compliance [31]. For noncompliant patients or women uncomfortable with follow-up, biopsy should be performed.

A complicated cyst can also be confirmed as a benign breast lesion by ultrasound-guided FNA that completely collapses the cyst. If the patient wishes to undergo a biopsy or is high risk for developing future breast cancer (as defined by one of the validated risk assessment models such as the Gail or the Tyrer-Cuzick model), ultrasound-guided FNA can be performed as an alternative to repeat imaging and clinical examination. (See "Genetic testing and management of individuals at risk of hereditary breast and ovarian cancer syndromes", section on 'Risk assessment models'.)

If the aspirated cyst does not completely collapse, further imaging (eg, mammography) and CNB are required.

Complex cyst — A complex cyst identified by ultrasound must be confirmed to be a benign or malignant lesion by image-guided CNB [18,32,33]. FNA is not sufficient, because a sample of the solid component or thickened septa needs to be obtained, not just cyst fluid.

A sonographically guided CNB is a safe and accurate technique for diagnosis of indeterminate or complex cystic breast lesions with a solid component [34-36]. When performing a CNB of a complex cystic breast lesion, it is essential to target the solid component with the first needle pass. Typically, a CNB consists of three to four biopsy samples. However, if the cystic portion is punctured with the first needle pass, the cystic component may collapse, making the solid component of the lesion difficult to identify sonographically.

At the completion of all CNBs, a metallic marker clip is deployed into the biopsy site to mark the area for future follow-up or surgical excision. If a CNB cannot be performed due to the position of the breast lesion or technical difficulty, a surgical biopsy with needle localization is indicated. (See "Breast biopsy", section on 'Biopsy methods'.)

Correlation of imaging and pathologic findings is essential [37]. If the findings on imaging and CNB pathology are discordant, surgical excision with needle localization is indicated.

If the findings on imaging and CNB pathology are concordant and benign, follow-up includes a clinical breast examination and imaging studies (breast ultrasound and mammography) every 6 to 12 months for one to two years to document stability [30]. Any changes in the biopsied lesion or growth of the lesion should lead to rebiopsy or excision [36,38,39]. A study of 156 patients who had a benign breast biopsy showed that 13 percent required a subsequent biopsy within two years [39].

Benign histologic findings associated with complex cysts include a wide range of diagnoses and should be treated appropriately [37,40]. (See "Overview of benign breast diseases".)

In a retrospective study, 150 patients with benign histology after ultrasound-guided vacuum-assisted biopsy for complex cystic breast lesions (BI-RADS 4) were evaluated to determine the appropriate follow-up. This subset of patients was followed at 6, 12, and 24 months with ipsilateral ultrasound and mammography. Breast MRI was used rarely (n = 4) for lesions initially seen on MRI. Of the 104 lesions with available follow-up imaging (mean 34.9 months), no lesions recurred or underwent malignant transformation [41].

Opportunistic ultrasonic breast screening in Japan was utilized to evaluate 10,519 women at five institutions to further evaluate recall criteria [42]. A cystic pattern was noted in 6512 cases. One of those cases was found to be malignant one year later, when an intracystic tumor was biopsied and found to be a microinvasive cancer (0.5 mm). Ninety cases found an intracystic tumor, with evaluation criteria including mass size and the depth/width ratio. No cancer was diagnosed in this subset of patients. Most of the study subjects were <40 years of age.

SUBSEQUENT BREAST CANCER RISK — The overall risk of a subsequent breast cancer is not increased for women with a history of simple breast cysts [40,43,44]. In a retrospective review of 480 subsequent breast cancer diagnoses among 14,602 women with benign breast biopsies, simple cysts were not associated with subsequent breast cancer development [43].

For patients with complicated or complex cysts, the risk of a subsequent breast cancer is related to the findings from the biopsy. As an example, mucocele-like lesions are cystic breast lesions that are often associated with atypical hyperplasia. In one study of 102 patients with mucocele-like lesions, 13 patients developed breast cancer at a median follow-up of 14.8 years [45].

Persistent, rapidly recurring cysts may require close follow-up. Although rare, one case report documented invasive ductal carcinoma in a simple cystic mass [46]. An enlarging breast cyst with irregular and hypoechogenic vegetation growing on the inner wall revealed a primary squamous cell carcinoma on biopsy [47].

The risk of a subsequent breast cancer developing in women with nonproliferative, proliferative, or atypical breast lesions is discussed separately. (See "Overview of benign breast diseases" and "Atypia and lobular carcinoma in situ: High-risk lesions of the breast".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Evaluation of breast problems".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Common breast problems (The Basics)")

●Beyond the Basics topics (see "Patient education: Common breast problems (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Breast cysts are fluid-filled round or ovoid masses. Breast cysts can present as symptomatic gross palpable masses or as microcysts, usually found as an abnormality on an imaging exam. Cysts usually prompt women to seek medical attention because of a palpable mass or associated discomfort. (See 'Introduction' above.)

●A breast cyst is suspected by either physical finding of a palpable breast mass or an abnormal imaging finding (most commonly a mammogram). A breast cyst is diagnosed by breast ultrasound, which also classifies it as simple, complicated, or complex. The sonographic appearance helps guide clinical management. (See 'Diagnosis' above and 'Classification' above.)

●Simple cysts, clustered simple microcysts, and most complicated cysts are benign (Breast Imaging-Reporting and Data System [BI-RADS] 2), and no intervention is needed. Fine needle aspiration (FNA) is only performed if the simple cyst is inflamed or infected (ie, skin erythema). (See 'Simple cyst' above.)

●Complicated cysts are rarely malignant, but those that are BI-RADS 3 should be followed with imaging and clinical examinations every six months for one year to document stability. Cysts that downgrade to BI-RADS 2 at one year do not need further follow-up. Cysts that remain BI-RADS 3 require further follow-up every six months. Core needle biopsy (CNB) is indicated if the lesion increases in size or changes in characteristics on repeat imaging. (See 'Complicated cyst' above.)

●Alternatively, complicated cysts that completely collapse after FNA are also benign. Patients who wish for biopsy, are high risk, are noncompliant, or are uncomfortable with follow-up should undergo FNA under ultrasound guidance. Complicated cysts that fail to completely collapse after FNA require further imaging (with mammography) and CNB. (See 'Complicated cyst' above.)

●Complex cysts (BI-RADS 4 or 5) should be biopsied with CNB. If the findings on imaging and CNB pathology are concordant and benign, follow-up includes a clinical breast examination and imaging studies (breast ultrasound and mammography) every 6 to 12 months for one to two years to document stability. (See 'Complex cyst' above.)

●Surgical excision is indicated for complex cysts that are not amenable to CNB and when pathology results from a CNB are discordant, atypical, indeterminate or reveal a malignancy. (See 'Complex cyst' above.)