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PubMed This is a summary of 10 peer-reviewed journal articles Updated
Radiology

Diagnosing Breast Cysts: Ultrasound and BI-RADS Scores

At a Glance

Ultrasound can show whether a breast lump is a simple fluid-filled cyst, a complicated cyst with debris, or a complex cystic and solid mass. The BI-RADS category then guides routine screening, short-term follow-up, or biopsy.

While a physical exam can detect a lump, it cannot “see” inside it to determine if it is solid or liquid [1]. For this reason, ultrasound is a primary tool for diagnosing breast cysts [2]. It uses sound waves to create a detailed map of the breast tissue, allowing radiologists to categorize lumps based on their internal structure and shape. Depending on your age and breast density—for example, if you are over 40—your doctor may also order a diagnostic mammogram or digital breast tomosynthesis, as the two tests together provide the most complete picture and targeted ultrasound complements mammography [3][4].

Why Ultrasound is Useful

Ultrasound is uniquely suited for finding cysts because sound waves travel through fluid differently than they do through solid tissue [2]. When sound waves hit a fluid-filled sac, they pass through easily, creating specific visual markers that a radiologist looks for on the screen. This allows them to distinguish a harmless, liquid-filled cyst from a solid mass that might require more investigation [2][5].

The Three Types of Breast Cysts

Radiologists use specific terminology to describe what they see on the ultrasound. You can often find these exact terms in your imaging report:

1. Simple Cysts

A simple cyst is a classic fluid-filled sac. On an ultrasound, it appears as a “perfect” cyst with these three features:

  • Anechoic: The inside of the cyst looks completely black because there are no solid echoes reflecting back from the fluid [2].
  • Circumscribed: The edges are smooth, round, or oval and clearly defined [2].
  • Posterior Enhancement: Because sound waves pass so easily through the fluid, the area directly behind the cyst appears brighter on the image [2].

2. Complicated Cysts

A complicated cyst is very similar to a simple cyst, but it contains some “debris”—perhaps slightly thickened fluid or protein [2]. It still has smooth edges and shows posterior enhancement, but the inside is not perfectly black; it may look cloudy or have faint echoes [5].

3. Complex Cystic and Solid Masses

A complex cyst (often called a “complex cystic and solid mass”) contains both fluid and solid components [6]. This is different from a complicated cyst because it may have:

  • Thick Walls or Septations: Thick internal “walls” dividing the cyst [6].
  • Solid Components: A solid “bump” (mural nodule) attached to the inner wall or a mass growing inside the fluid [6][7].
  • Vascularity: Blood flow detected within the solid parts of the cyst [8].

Decoding Your BI-RADS Category

To make imaging results clear and consistent, doctors use a system called BI-RADS (Breast Imaging-Reporting and Data System). This is a probability-and-management category rather than a strict diagnosis, indicating what the next step should be [9].

BI-RADS Category Meaning Usual Cyst Type Recommended Action
Category 2 Benign (0% risk of cancer) [2]. Simple Cysts; Clustered Microcysts [2]. No further action; return to normal screening [5].
Category 3 Probably Benign (>0% but ≤2% risk) [9]. Complicated Cysts [2]. Short-term follow-up to ensure no change [5].
Category 4 Suspicious (>2% but <95% risk, subdivided into 4A, 4B, 4C) [9]. Complex Cystic and Solid Masses [6]. Biopsy (taking a small sample of the solid part) is generally recommended [10].

Note that Categories 0, 1, 5, and 6 also exist; Category 5 is at least 95% suspicious of cancer and mandates biopsy. By understanding these terms, you can more effectively discuss your results with your care team. If your report says “BI-RADS 2” and describes a “simple anechoic cyst,” you can feel confident that the finding is benign [2][5]. The clinical finding must also be concordant with the imaging report for complete reassurance.

Common questions in this guide

Can an ultrasound tell whether a breast lump is a cyst?
Ultrasound can often show whether a breast lump is fluid-filled or solid by examining its internal structure. It may identify a simple cyst, a cyst with debris, or a mass with both fluid and solid parts. Mammography or breast tomosynthesis may also be recommended depending on your age and breast density.
What does a simple breast cyst look like on ultrasound?
A typical simple cyst appears completely black inside, has smooth and clearly defined edges, and looks brighter behind the cyst because sound waves pass through the fluid. These features are usually benign and are often assigned BI-RADS 2, which generally means routine screening is appropriate.
What is the difference between a complicated and complex breast cyst?
A complicated cyst contains debris or thickened fluid but usually keeps smooth edges and shows increased brightness behind it. A complex cystic and solid mass may have thick walls, internal divisions, a solid nodule, or blood flow in a solid area, so it generally needs more evaluation.
What does BI-RADS 3 mean for a breast cyst?
BI-RADS 3 means the finding is probably benign, with a small chance of cancer, and short-term follow-up imaging is usually recommended. The purpose is to check for changes over time; a biopsy may be considered if the finding changes or develops more concerning features.
Does BI-RADS 4 mean that a breast cyst is cancer?
No. BI-RADS 4 means the imaging finding is suspicious enough that a biopsy is generally recommended, but the category is not a cancer diagnosis. A biopsy, often sampling the solid part of the mass, is used to determine what the finding is.
What if the ultrasound does not explain the lump I can feel?
The imaging finding should match the location and clinical examination of the lump; this is called clinical and imaging concordance. Ask your clinician whether the report fully explains the palpable lump and whether additional evaluation or imaging is needed.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Does my imaging report describe my cyst as anechoic, and does it show posterior enhancement?
  2. 2.What is the specific BI-RADS assessment on my report, and what does it recommend?
  3. 3.If my score is BI-RADS 3, what specific changes in the follow-up imaging would trigger a biopsy?
  4. 4.If my score is BI-RADS 4, what type of biopsy do you recommend, and will it be a core needle biopsy?
  5. 5.Do the imaging findings completely explain the lump I am feeling?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (10)
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    [Exploring a non-inflammatory clinical breast mass: Clinical practice guidelines].

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    Cystic Breast Lesions: Diagnostic Approach and US Assessment.

    Lim HS, Lee HJ, Lee JS, et al.

    Radiographics : a review publication of the Radiological Society of North America, Inc 2025; (45(5)):e240179 doi:10.1148/rg.240179.

    PMID: 40244873
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    Breast Ultrasound: Indications and Findings.

    Gundry KR

    Clinical obstetrics and gynecology 2016; (59(2)):380-93 doi:10.1097/GRF.0000000000000194.

    PMID: 26974219
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    Clinical practice guidelines from the French College of Gynecologists and Obstetricians (CNGOF): benign breast tumors - short text.

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    European journal of obstetrics, gynecology, and reproductive biology 2016; (200()):16-23.

    PMID: 26967341
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    [Management of a breast cystic syndrome: Guidelines].

    Uzan C, Seror JY, Seror J

    Journal de gynecologie, obstetrique et biologie de la reproduction 2015; (44(10)):970-9.

    PMID: 26527028
  6. 6

    Outcomes in Sonographically Categorized Complex Cystic Breast Lesions.

    Kulali F, Guner G

    Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine 2022; (41(8)):2071-2077 doi:10.1002/jum.15891.

    PMID: 34825721
  7. 7

    Value of Hand-held Ultrasound in the Differential Diagnosis and Accurate Breast Imaging Reporting and Data System Subclassification of Complex Cystic and Solid Breast Lesions.

    Xiang H, Tang G, Li Y, et al.

    Ultrasound in medicine & biology 2020; (46(5)):1111-1118 doi:10.1016/j.ultrasmedbio.2020.01.006.

    PMID: 32107090
  8. 8

    Conventional ultrasound combined with BI-RADS classification in differential diagnosis of benign and malignant complex cystic and solid breast lesions.

    Jin Y, Wu J, Hu Z, et al.

    Medicine 2025; (104(40)):e44763 doi:10.1097/MD.0000000000044763.

    PMID: 41054167
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    Understanding BI-RADS Category 3.

    Fazeli S, Stepenosky J, Guirguis MS, et al.

    Radiographics : a review publication of the Radiological Society of North America, Inc 2025; (45(1)):e240169 doi:10.1148/rg.240169.

    PMID: 39636752
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    Adult cystic lymphangioma in the inner quadrant of the breast-Rare location for a rare disease: A case report.

    Rusdianto E, Murray M, Davis J, Caveny A

    International journal of surgery case reports 2016; (20()):123-6.

    PMID: 26852362

This page explains breast cyst ultrasound findings and BI-RADS categories for informational purposes only and does not constitute medical advice. Your radiologist or clinician should interpret your report and recommend care for your situation.

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