Breast Ultrasound: BI-RADS, What It Detects and How to Read the Report
Guide for patients and professionals · Reviewed by a specialist · Colombia 2026
Breast ultrasound: what it is, when it is indicated, how to read the report, and what each result means
The most comprehensive guide to breast ultrasound in Spanish — to understand BI-RADS v2025, the difference between a cyst and a solid nodule, and when ultrasound is not enough
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Reviewed by the GSMED Imaging medical team
Specialists in diagnostic ultrasound and breast imaging. Content based on ACR BI-RADS v2025 (November 2025), the ACR Appropriateness Criteria 2024, the Mexican Breast Cancer Consensus 2025, and Radiographics January 2025.
ℹ️ Important medical notice: This guide is for informational and educational purposes only. It does not replace or substitute the evaluation of a medical specialist. If you have a palpable nodule, a BI-RADS result awaiting interpretation, or any questions about your breast health, consult your gynecologist, mastologist, or radiologist. The information contained herein does not constitute a medical diagnosis.
Finding a breast nodule, receiving a report with "BI-RADS 3," or having a doctor say you have "dense breasts" causes immediate and understandable anxiety. Breast ultrasound is the test that most frequently resolves — or delves deeper into — that anxiety. Understanding exactly what it looks for, what it can see, and what each number in the report means is the difference between a patient who acts with information and one who acts out of fear.
1. What is breast ultrasound, and how does it differ from mammography?
Breast ultrasound — also called breast sonography or breast ultrasound — is an imaging technique that uses high-frequency sound waves to generate real-time images of the internal structures of the mammary gland. It does not use ionizing radiation, it is painless, and it does not require breast compression like mammography.
The fundamental difference from mammography is not one of quality — it is one of nature. Mammography sees two-dimensional shadows of compressed tissue using X-rays, and it is unsurpassed for detecting microcalcifications and architectural distortions. Ultrasound sees the internal structure of tissues using sound waves, and it is unsurpassed for characterizing a mass that has already been detected: determining whether it is solid or liquid, precisely defining its borders, and guiding interventional procedures.
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Breast ultrasound
- No radiation — safe during pregnancy
- Distinguishes a cyst from a solid nodule
- Ideal for dense breasts
- Guides biopsies and procedures
- Real-time — dynamic
- No preparation or compression
- First-line for <35 years
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Mammography
- Detects microcalcifications
- Standard screening >40 years
- Reduces cancer mortality
- Better for fatty breasts
- Limited for dense breasts
- Requires compression
- Low but present radiation
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Breast MRI
- Maximum sensitivity (~90–95%)
- High risk: BRCA1/2, family history
- Evaluates response to chemotherapy
- No radiation
- High cost and low availability
- Requires IV contrast (gadolinium)
- High risk of false positives
The golden rule every doctor applies Breast ultrasound does not replace mammography, nor vice versa. They are complementary. In women under 35 with a palpable mass, ultrasound is first-line. In women over 35–40, mammography is the starting point, and ultrasound is the complementary diagnostic tool. Together, their diagnostic sensitivity far exceeds that of either method alone.
100%
sensitivity of breast ultrasound for a palpable mass in pregnant women (ACR 2024)
+3.3
additional cancers detected for every 1,000 studies when adding ultrasound to mammography in dense breasts
30 min
approximate duration of the complete bilateral study
v2025
latest ACR BI-RADS update — November 2025
2. Indications: when the doctor orders a breast ultrasound
🔍 Evaluation of a palpable mass
- Nodule detected by self-examination or by the doctor
- First-line in women under 35
- Mandatory complement to mammography in those over 35
- Men with gynecomastia or a palpable nodule
📊 Complement to an abnormal mammogram
- BI-RADS 0 mammogram — incomplete study
- Breast density C or D (dense breasts)
- Characterize a suspicious mammographic finding
- Confirm whether a lesion is solid or cystic
🫃 Pregnancy and breastfeeding
- First-line in pregnant women with a palpable mass (no radiation)
- Evaluation of mastitis or abscess during breastfeeding
- Suspected galactocele
- Follow-up of previously characterized lesions
🩸 Specific symptoms
- Bloody nipple discharge
- Localized breast pain with no clear cause
- Changes in the breast skin
- New or progressive breast asymmetry
🎯 Procedure guide
- Ultrasound-guided core needle biopsy (CNB)
- Puncture and aspiration of symptomatic cysts
- Preoperative marking of lesions
- Monitoring treatment response
👙 Breast implants
- Suspected implant rupture
- Evaluation of capsular contracture
- Evaluation of periprosthetic tissue
- Routine post-implant follow-up
3. The three most common scenarios — and what to expect in each
These are the most common clinical situations that lead a woman to get a breast ultrasound in Colombia. Understanding which scenario applies to you helps you better interpret what the specialist is looking for:
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Scenario 1 — "I found a lump or nodule"
"I felt something in my left breast. The doctor ordered an ultrasound. What exactly will they look for?"
The specialist will evaluate whether that nodule is a simple cyst (filled with fluid, benign by definition), a complex cyst (with septations or internal contents), a solid nodule with benign characteristics (fibroadenoma — the most common cause in young women), or a solid nodule with suspicious characteristics. Ultrasound resolves most questions during the same visit, without the need for an immediate biopsy in most cases.
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Scenario 2 — "The mammogram was abnormal or incomplete"
"My mammogram says BI-RADS 0 or that I have dense breasts. What does that mean, and what is the ultrasound for?"
BI-RADS 0 means that the mammogram was not sufficient to classify the finding — it needs more information. Ultrasound complements the mammogram by precisely characterizing what that suspicious area is. In dense breasts (category C or D), fibroglandular tissue hides lesions on the mammogram; ultrasound has better sensitivity in that specific context and can detect cancers that the mammogram missed.
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Scenario 3 — "I am pregnant or breastfeeding and have a lump"
"I am pregnant and a nodule appeared. Can I get an ultrasound? Is it safe for the baby?"
Yes — breast ultrasound is completely safe during pregnancy and breastfeeding because it does not use radiation. In fact, it is the first-line imaging in this context. ACR guidelines (2024) state that no palpable mass in a pregnant woman should go unevaluated by imaging, and ultrasound is the modality of choice with 100% sensitivity for palpable masses in this group. Most cases are benign (galactoceles, lactational adenomas, cysts), but pregnancy-associated breast cancer exists and must be ruled out.
4. How a breast ultrasound is performed: the step-by-step procedure
- Preparation: no special preparation is required. It is recommended not to apply creams or deodorant to the breast and axillary area on the day of the study. If possible, schedule it during the first half of the menstrual cycle (weeks 1 to 14) — the breast tissue is less sensitive, and the study is more comfortable.
- Positioning: the patient lies supine (on her back) with the arm on the side being studied raised above her head. For the outer breast, the specialist may ask her to turn slightly toward the opposite side.
- Application of gel and scanning: cold aqueous conductive gel is applied to the breast. The linear transducer (usually 10–15 MHz for superficial breast structures) is systematically moved to cover all breast quadrants, the nipple, and the axillary region.
- Real-time examination: the specialist observes the real-time image on the screen, adjusting the depth, frequency, and focus to optimize the visualization of each area. If they detect a lesion, they characterize it in detail: shape, orientation, margins, echogenicity, and posterior acoustic effect.
- Vascular Doppler: in suspicious lesions, color Doppler may be added to evaluate the vascularization of the lesion — malignant lesions usually have greater peripheral or internal vascularization.
- Duration: a complete bilateral study takes between 20 and 40 minutes depending on the findings and the complexity of the breast tissue.
What you can do during the study You can ask questions while the specialist examines. Questions such as "is that a cyst or is it solid?" or "how do the borders look?" are completely valid. A good specialist will explain it to you at the time. If the image is not completely clear, you can ask them to show you the monitor — you have the right to understand what is being seen of your own body.
5. The BI-RADS report: the key to understanding your result
The BI-RADS (Breast Imaging Reporting and Data System) is the universal language used by radiologists worldwide to report the results of breast ultrasound, mammography, and MRI. It was developed by the American College of Radiology (ACR), and its most recent version — BI-RADS v2025, published in November 2025 — harmonizes the system for the different imaging modalities and moves toward structured workflows supported by artificial intelligence.
Each report concludes with a category from 0 to 6. This category is not just a number — it is associated with a probability of malignancy and a specific clinical course of action:
0
Incomplete
Incomplete evaluation — more images are needed
The radiologist does not have enough information to classify the finding. It may be necessary to compare it with previous studies, add additional mammographic views, or perform a complementary ultrasound.
→ Action: complete the study before deciding
1
Negative
No significant findings — normal result
No masses, microcalcifications, or architectural distortions are observed. The breasts are symmetrical. Risk of malignancy: 0%.
→ Action: routine follow-up according to age and risk
2
Benign
Benign finding — no oncological concern
A lesion is described whose characteristics are definitively benign: simple cyst, fibroadenoma with strict criteria of benignity, nodule with benign coarse calcifications, hamartoma, implant. Risk of malignancy: 0%.
→ Action: routine follow-up — no biopsy
3
Probably benign
Probably benign — low risk but requires follow-up
Finding with characteristics suggesting benignity but without sufficient certainty to classify it as BI-RADS 2. The probability of malignancy is less than 2%. Examples: oval solid nodule, with circumscribed margins, parallel orientation in a young woman without risk factors. BI-RADS 3 is not assigned without a prior complete evaluation.
→ Action: ultrasound follow-up at 6 months (and at one and two years if it remains stable)
4
Suspicious
Suspicious finding — biopsy recommended
Broadest category: groups lesions with a probability of malignancy from 2% to 95%. That is why the ACR subdivides it into 4A (low suspicion: 2–10%), 4B (intermediate suspicion: 10–50%), and 4C (moderately high suspicion: 50–95%). The subdivision guides the urgency and the type of biopsy.
→ Action: core needle biopsy (CNB) guided by ultrasound or stereotaxis
5
Highly suspicious
Highly suggestive of malignancy
Typically malignant findings with a probability of malignancy greater than 95%. The diagnosis of cancer is virtually certain ultrasonographically, but it is always confirmed by biopsy before starting oncological treatment.
→ Action: urgent biopsy — referral to breast oncology or mastology
6
Confirmed malignancy
Malignancy already confirmed by previous biopsy
Category used for imaging follow-up once the biopsy has already confirmed the cancer diagnosis. It is used to assess response to treatment (neoadjuvant chemotherapy) or surgical planning.
→ Action: continue established oncological treatment
What BI-RADS 3 DOES NOT mean Receiving a BI-RADS 3 does not mean you have cancer or are close to having it. It means there is something that looks probably benign, but the specialist wants to confirm it over time. The probability that a BI-RADS 3 is malignant is less than 2%. The important thing is to respect the follow-up controls — at 6 months, one year, and 2 years — to confirm that there are no changes.
6. How the sonographer describes a nodule: BI-RADS descriptors in ultrasound
When the radiologist finds a solid nodule on ultrasound, they describe it using standardized vocabulary. Understanding these descriptors helps you read your report more clearly:
Shape
Oval / rounded: → Suggestive of benign
Irregular: → Suspicion of malignancy
Orientation
Parallel (long axis horizontal): → Suggestive of benign
Non-parallel (vertical, taller than wide): → High suspicion
Margins
Circumscribed, well-defined: → Suggestive of benign
Non-circumscribed (spiculated, angular, microlobulated, indistinct): → Suspicious
Echogenicity
Anechoic (black, liquid): → Simple cyst — benign
Hyperechoic or isoechoic: → More common in benign lesions
Heterogeneous hypoechoic: → Increases suspicion
Posterior features
Posterior enhancement: → Cyst (pure liquid)
No posterior change: → Usual benign solid tissue
Posterior acoustic shadow: → Suspicious if it is not calcification
Calcifications
Coarse calcifications within the lesion: → Benign
Microcalcifications within the solid nodule: → Suspicious
Simple cyst vs complex cyst vs solid nodule
| Lesion type | Ultrasound appearance | Usual BI-RADS | Clinical action |
|---|---|---|---|
| Simple cyst | Completely anechoic, thin wall, well-defined margins, posterior enhancement, no internal content | BI-RADS 2 | No action — benign by definition |
| Complicated cyst | Homogeneous hypoechoic content (uniform echoes), no internal Doppler flow. May be infection, intracystic hemorrhage | BI-RADS 3 | Follow-up at 6 months — aspiration if symptomatic |
| Complex cyst (category 1) | Cyst with thin septa, thin wall without mural nodule — "bunch of grapes" | BI-RADS 3 | Follow-up at 6 months |
| Complex cyst (category 2–3) | Cyst with mural nodule, irregular wall thickening, thick septa with Doppler flow | BI-RADS 4 | Biopsy |
| Benign solid nodule (fibroadenoma) | Oval, parallel, circumscribed margins, homogeneous hypoechoic, no shadow | BI-RADS 3 | Follow-up at 6 months — biopsy if in doubt |
| Suspicious solid nodule | Irregular, non-parallel, spiculated or angular margins, heterogeneous hypoechoic | BI-RADS 4–5 | Urgent biopsy |
7. Ultrasound in dense breast: why it matters and what changes
Breast density is the proportion of fibroglandular tissue versus fatty tissue in the breast. Dense breasts (BI-RADS categories C and D) have so much white fibroglandular tissue that it can mask lesions on mammography — cancer, which is also white on mammography, "camouflages" itself in the dense background.
This has two implications that every woman with dense breasts should know:
- The sensitivity of mammography decreases significantly in dense breasts. Studies cited by the ACR show that the cancer detection rate in dense breasts is 1.8 per 1,000 women with mammography alone, and rises to 2.4 per 1,000 when complementary ultrasound is added. That difference translates into real cancers detected that otherwise would not have been found until they were more advanced.
- Dense breast is by itself an independent risk factor for breast cancer. It does not mean you have it — but density raises the baseline risk. Women with very dense breasts (category D) and other risk factors are candidates for complementary studies (screening ultrasound, magnetic resonance imaging).
Regulatory update 2024 — FDA (USA) Since 2024, the FDA in the United States requires all mammography centers to inform the patient if they have dense breasts. This regulation, although it applies directly in the US, drives the global trend toward transparency about breast density and the use of complementary studies in dense breasts. In Colombia, the communication of density is at the discretion of the specialist — there is no equivalent regulation yet, but it must appear in the BI-RADS report.
8. Warning signs that should not wait for a scheduled ultrasound
⚠️ Consult urgently if you have any of these signs
Nodule that has visibly grown in days or weeks
Skin change: orange peel skin, redness, induration
Recent onset nipple retraction
Bloody nipple discharge (unilateral, spontaneous)
Hard, fixed, or enlarged axillary lymph nodes
Intense, localized, sudden onset breast pain
Change in breast shape or contour without apparent cause
Very hard, non-mobile, nodule attached to skin or muscle
9. When breast ultrasound is not enough (diagnostic honesty)
Breast ultrasound has real limitations that no serious article can omit:
- It does not detect microcalcifications: microcalcifications — one of the most important ultrasound signs of ductal carcinoma in situ (DCIS) — are invisible or practically impossible to characterize on ultrasound. Mammography is irreplaceable for this finding.
- Operator-dependent sensitivity: unlike mammography or MRI, the quality of breast ultrasound depends critically and directly on the operator's experience. A study performed by an ultrasound technician without specific breast training can give false negatives in small or deeply located lesions.
- It is not a validated screening method in the general population: mammography is the only screening method with demonstrated evidence of reduction in breast cancer mortality in the general population. Ultrasound can be complementary screening in dense breasts or high risk, but it does not replace mammography as a primary screening tool.
- Limited for deep lesions in very large breasts: in large breasts with a lot of deep tissue, lesions located on the posterior face of the breast tissue can be difficult to visualize with the standard superficial transducer.
- It does not characterize clustered microcalcifications with certainty: when mammography detects a group of suspicious microcalcifications, stereotactic biopsy (mammography-guided) is the method of choice — not ultrasound.
The quality of breast ultrasound also depends on the equipment
Diagnostic-quality breast ultrasound requires an ultrasound machine with a high-frequency linear probe (10–15 MHz), color Doppler, and elastography capability. At GSMED we have diagnostic-grade breast ultrasound equipment available in Colombia with local technical support.
10. Frequently asked questions about breast ultrasound
Does breast ultrasound hurt?
No. It is completely painless. A probe with gel is slid over the breast skin without any compression. It is much more comfortable than mammography. The only possible sensation is the cold of the conductive gel.
Can I have a breast ultrasound if I am menstruating?
Yes, it can be done at any time in the cycle. However, the first half of the cycle (days 7–14) is the most comfortable time because the breast tissue is less sensitive and congested. In the second half and during menstruation, breasts are usually more tense and sensitive, which can make the examination slightly more uncomfortable although it does not prevent the study.
What is the difference between a normal ultrasound and a high-resolution one?
The term "high-resolution ultrasound" refers to the use of high-frequency probes (10–15 MHz) that produce images with greater detail of the superficial breast structures. It is the current standard for diagnostic breast ultrasound. An ultrasound with a low-frequency probe (3–5 MHz, designed for the abdomen) has much less resolution in the breast and should not be used to evaluate breast lesions with diagnostic criteria.
I was told I have a "simple cyst" — do I need to do anything?
Not necessarily. A simple cyst on ultrasound is benign by definition — BI-RADS 2, 0% risk of malignancy. It does not need a biopsy or specific follow-up unless it is very large and causes physical discomfort, in which case it can be aspirated. What is advisable is to maintain the usual gynecological controls according to your age and risk factors.
How long do breast ultrasound results take?
In many centers, the radiologist explains the main findings to you at the end of the study — especially if any immediate action is needed. The formal written report is usually available in 24–72 hours depending on the center. If they detected something that requires a biopsy, the specialist will coordinate it in the same visit or as soon as possible.
Do I need to prepare in any special way before the breast ultrasound?
No special preparation is required. Practical recommendations: do not apply cream, gel, or deodorant to the breast and axillary area on the day of the study (the gel interferes with the transducer). Bring previous studies if you have them — comparison with previous ultrasounds is very valuable for the specialist. Dress in two-piece clothing to facilitate access to the examination area.
At what age should I start having breast ultrasounds?
Breast ultrasound is not a routine screening method by age — it is indicated when there is a specific clinical indication (palpable nodule, mammographic finding, symptom) or as a complement to mammography. Routine imaging screening starts with mammography at age 40 (or earlier in high-risk women). Ultrasound can be added as complementary screening in dense breasts or high risk. Consult with your gynecologist about the correct screening strategy for you according to your risk profile.
A quality breast diagnosis starts with the right ultrasound machine
Ultrasound machines with high-frequency linear probe, color Doppler, and breast elastography available in Colombia — with local technical support and financing.
View breast ultrasound machines →Related articles
Primary sources and bibliographic references
- American College of Radiology (ACR). ACR BI-RADS Atlas, 5th Edition. 2013 — with BI-RADS v2025 update, published November 2025. 2025 Update
- ACR Appropriateness Criteria®. Breast Imaging — Imaging of Pregnant and Lactating Women. 2024. ACR Guide
- ACR Appropriateness Criteria®. Supplemental Breast Cancer Screening Based on Breast Density. 2021. ACR Guide
- Lauar MCV, Merigue G, Dias LF et al. Breast US: Guide for Beginners. Radiographics. 2025;45(1):e240161. DOI: 10.1148/rg.240161. Radiographics 2025
- Mexican Consensus on the Diagnosis and Treatment of Breast Cancer. 12th Revision. Colima, Mexico, 2025. Latin America 2025
- American Cancer Society. Breast Ultrasound. Updated 2024. cancer.org. Patient Reference
- Aibar L, Santalla A. Radiological classification and management of breast lesions. Clínica e Investigación en Ginecología y Obstetricia. Elsevier, 2011. Academic Reference
- AQUAS/REDETS. Support tool in ultrasound diagnosis for the classification of breast nodules. Agencia de Qualitat i Avaluació Sanitàries de Catalunya, 2024. 2024 Evidence
- Wikipedia BI-RADS (ES). BI-RADS System — v2025 update. Revised April 2026. Secondary Reference
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