Introduction to the Breast Imaging Reporting and Data System

Harmien Zonderland

Radiology department of the Leiden University Medical Centre, Leiden, the Netherlands


This article is based on the publication of the ACR BI-RADS Atlas 2013 and supplemented with some recommendations from the Netherlands Guideline Breast Cancer 2012 and the Dutch College of Breast Imaging.


The illustrated BI-RADS atlas

In 2000 the Dutch Institute for Health Care Improvement (CBO) has chosen to use the Breast Imaging Reporting and Data System (BI-RADS) for breast imaging.
All other systems that were previously used were abandoned, because unlike the BI-RADS system, they lacked quantification and used very subjective and undefined terms and were not evidence-based.
Breast Imaging Reporting and Data System - BI-RADS Atlas

  • Bi Rads

BI-RADS is a quality assurance tool designed to standardize mammography reporting, reduce confusion in breast imaging interpretations, and facilitate outcome monitoring.
It contains a lexicon for standardized terminology (descriptors) for mammography, breast US and MRI, aswell as Standard Reporting with Final Assessment Categories and guidelines for Follow-up and Outcome Monitoring.
It even enables you to evaluate the quality of your reporting.

Report Organization

  • Report Organization

The reporting system is designed to provide an organized approach to image interpretation and reporting.

1. Describe the indication for the study.
2. Describe the breast composition.
3. Describe any significant finding.
4. Compare to previous studies.
5. Conclude to a final assessment category.
6. Give management recommendations.

When you describe a lesion use standard BI-RADS descriptors for Mammography, Ultrasound and MRI (see below).
If an additional imaging modality is added, mention type and rationale for each modality.
If more than one imaging modality is performed, for instance US with Mammography or with MRI, an integrated report with assessment based on the highest level of suspicion must be used.
When you use more modalities, always make sure, that you are dealing with the same lesion.
For instance a lesion found with US does not have to be the same as the mammographic or physical findings. Sometimes repeated mammographic imaging with markers on the lesion found with US can be helpful.

Breast Imaging Lexicon

Mammographic Breast Composition

Mammographic breast composition is described as follows:
1. the breast is almost entirely fat ( 2. scattered fibroglandular densities (25-50%)
3. heterogeneously dense breast tissue (51-75%)
4. extremely dense (> 75% glandular)


A 'Mass' is a space occupying lesion seen in two different projections. If a potential mass is seen in only a single projection it should be called a 'Density' until its three-dimensionality is confirmed.

Circumscribed (well-defined or sharply-defined) margins: The margins are sharply demarcated with an abrupt transition between the lesion and the surrounding tissue. Without additional modifiers there is nothing to suggest infiltration.
Indistinct (ill defined) margins: The poor definition of the margins raises concern that there may be infiltration by the lesion and this is not likely due to superimposed normal breast tissue.
Spiculated Margins: The lesion is characterized by lines radiating from the margins of a mass.

Architectural distortion

The normal architecture is distorted with no definite mass visible. This includes spiculations radiating from a point, and focal retraction or distortion of the edge of the parenchyma. Architectural distortion can also be an associated finding.

Focal asymmetry

This is a density that cannot be accurately described using the other shapes.
It is visible as asymmetry of tissue density with similar shape on two views, but completely lacking borders and the conspicuity of a true mass.
It could represent an island of normal breast, but its lack of specific benign characteristics may warrant further evaluation.
Additional imaging may reveal a true mass or significant architectural distortion.
Due to confusion of the term mass with the term 'density' which describes attenuation characteristics of masses, the term 'density' has been replaced with 'asymmetry'.

  • Amorphous, indistinct microcalcifications
Amorphous, indistinct microcalcifications


Amorphous or Indistinct Calcifications:
These are often round or 'flake' shaped calcifications that are sufficiently small or hazy in appearance that a more specific morphologic classification cannot be determined.

  • Heterogeneous microcalcifications
Heterogeneous microcalcifications

Coarse, Heterogeneous Calcifications:
Irregular calcifications with varying sizes and shapes that are usually larger than 0.5 mm in diameter.

  • Fine, pleomorphic and branching microcalcifications
Fine, pleomorphic and branching microcalcifications

Fine, Pleomorphic or Branching Calcifications:
Fine pleomorphic calcifications are more conspicuous than the amorphic forms.
They vary in sizes and shapes and are usually smaller than 0,5 mm.
Fine branching calcifications are thin, linear or curvilinear, may be discontinuous and smaller than o,5 mm.
Their appearance suggests filling in of the lumen of a duct involved irregularly by breast cancer.

  • Benign calcifications
Benign calcifications

Benign Calcifications:
Benign calcifications are usually larger than calcifications associated with malignancy.
They are usually coarser, often round with smooth margins and are much more easily seen.

When you describe an abnormality (mass, architectural distortion, focal asymmetry or calcifications) always use the standard BI-RADS descriptors and mention the lesion size and location.

Final Assessment Categories

  • Final Assessment Categories

A negative diagnostic examination is one that is negative, with a benign or probably benign finding (BI-RADS 1, 2 or 3).
In BI-RADS 3 the radiologist prefers to establish the stability of a lesion by short term follow-up.
In the evaluation of your BI-RADS 3 lesions the malignancy rate should be A positive diagnostic examination is one that requires a tissue diagnosis (BI-RADS 4 and 5).
In BI-RADS 4 the radiologist has sufficient concern to urge a biopsy (2-95% chance of malignancy).
In BI-RADS 5 the chance of malignancy should be > 95%.

  • Category 0
BI-RADS 0 at screening.Additional ultrasound after referral was performed allowing final assessment.

Need Additional Imaging Evaluation and/or Prior Mammograms For Comparison:

BI-RADS 0 is utilized when further imaging evaluation (e.g. additional views or ultrasound) or retrieval of prior films is required.
When additional imaging studies are completed, a final assessment is made.
Always try to avoid this category by immediately doing additional imaging or retrieving old films before reporting.
Even better to have the old films before starting the examination.

  • Category 1
BI-RADS Category 1


There is nothing to comment on.
The breasts are symmetric and no masses, architectural distortion or suspicious calcifications are present.

  • BI-RADS Category 2
BI-RADS Category 2. A mass seen on mammogram proved to be a cyst.

Benign Finding:

Like BI-RADS 1, this is a normal assessment, but here, the interpreter chooses to describe a benign finding in the mammography report. Involuting, calcified fibroadenomas, multiple secretory calcifications, fat-containing lesions such as oil cysts, lipomas, galactoceles and mixed-density hamartomas all have characteristically benign appearances, and may be labeled with confidence.
The interpreter may also choose to describe intramammary lymph nodes, vascular calcifications, implants or architectural distortion clearly related to prior surgery, while still concluding that there is no mammographic evidence of malignancy.

  • 3a
BI-RADS 3. Non-palpable sharply defined lesion with a cluster of punctate calcifications.

Probably Benign Finding - Initial Short-Interval Follow-Up Suggested:

A finding placed in this category should have less than a 2% risk of malignancy.
It is not expected to change over the follow-up interval, but the radiologist would prefer to establish its stability.
Lesions appropriately placed in this category include:

  • Nonpalpable, circumscribed mass on a baseline mammogram (unless it can be shown to be a cyst, an intramammary lymph node, or another benign finding),
  • Focal asymmetry which becomes less dense on spot compression view
  • Cluster of punctate calcifications
  • 3b
Follow up at 6, 12 and 24 months showed no change. Final assessment was changed to a Category 2.

The initial short-term follow-up is a unilateral mammogram at 6 months, then a bilateral follow-up examination at 12 months and 24 months after the initial examination.
If the findings shows no change in the follow up the final assessment is changed to BI-RADS 2 (benign) and no futher follow up is needed.

  • 3-4 lesion
Upper: Category 3 lesion. There are two indeterminate or amorphous calcifications.Lower: 12 month follow up.Final diagnosis: Invasive carcinoma within an area of DCIS.

If a BI-RADS 3 lesion shows any change during follow up, it will change into a BI-RADS 4 or 5 and appropriate action should be taken.

The case on the left shows a few amorphous calcifications initially classified as BI-RADS 3.
At 12 month follow up more calcifications were noted in a cluster.
The findings were now classified as BI-RADS 4.
This proved to be DCIS with invasive carcinoma.

  • .
LEFT: Solid, circumscribed, oval mass with horizontal orientation, most likely fibroadenoma, BI-RADS 3RIGHT: Solid, circumscribed mass with horizontal orientation and irregular shape. It can be an older sclerotic fibroadenoma, but because of its atypical appearance it should be assigned a BI-RADS 4(a)

A solid mass with circumscribed margins, oval shape and horizontal orientation is most likely a fibroadenoma and can be assigned a BI-RADS 3, irrespective if the lesion is palpable or not.
As a consequence, solid lesions that do not possess all the typical characteristics of a fibroadenoma should be assigned a BI-RADS 4 and always be biopsied.

  • after Conservative treatment for breast cancer
First and second control after conservative treatment for breast cancer (BI-RADS 3 and BI-RADS 2)

First control after conservative treatment for breast cancer: new scars and postirradiation thickening of skin and interstitium is assigned BI-RADS 3.
2nd control after Conservative treatment for breast cancer: decrease of sequalae of treatment, BI-RADS category can be changed into BI-RADS 2 (figure)

  • Category 4
Category 4: There is an abnormality suspicious for malignancy, but a benign lesion, although unlikely, is a possibility ( for instance ectopic glandular tissue within a heterogeneous breast).

Suspicious Abnormality - Biopsy Should Be Considered:

BI-RADS 4 is reserved for findings that do not have the classic appearance of malignancy but have a wide range of probability of malignancy (2 - 95%).
By subdividing Category 4 into 4A, 4B and 4C , it is encouraged that relevant probabilities for malignancy be indicated within this category so the patient and her physician can make an informed decision on the ultimate course of action.

  • Category 4

The case on the left shows another BI-RADS 4 abnormality.
The pathologist could report to you that it is sclerosing adenosis or ductal carcinoma in situ.
In both cases you as a radiologist would agree.

  • Category 5

Highly Suggestive of Malignancy. Appropriate Action Should Be Taken:

BI-RADS 5 must be reserved for findings that are classic breast cancers, with a >95% likelihood of malignancy.
A spiculated, irregular high-density mass, a segmental or linear arrangement of fine linear calcifications or an irregular spiculated mass with associated pleomorphic calcifications are examples of lesions that should be placed in BI-RADS 5.

  • Category 5-2

BI-RADS 5 contains lesions for which one-stage surgical treatment could be considered without preliminary biopsy.
However, current oncologic management may require percutaneous tissue sampling as, for example, when sentinel node imaging is included in surgical treatment or when neoadjuvant chemotherapy is administered.

  • Category 6
LEFT: initial mammogram with marker on palpable mass. Biopsy proven carcinoma.RIGHT: Follow up after chemotherapy. Tumor is hardly visible.

Known Biopsy Proven Malignancy. Appropriate Action Should Be Taken

BI-RADS 6 is reserved for lesions identified on the imaging study with biopsy proof of malignancy prior to definitive therapy.
This category was added to the classification because sometimes patients are treated with neo-adjuvant chemotherapy.
During the course of the treatment the tumor may be less visible, while still you know you are dealing with cancer (figure).

  • Category 6
Category 6: Initial tumor measures 3.6 cm. After treatment 1.8 cm.

Same case as above. Initial ultrasound shows large tumor. After chemotherapy shrinkage of the tumor.