BI-RADS

BI-RADS stands for 'breast imaging reporting and data system', and was established by the American College of Radiology. BIRADS is a scheme for putting the findings of mammograms, (for breast cancer diagnosis), into a small number of well-defined categories. Although BIRADS started out only for mammograms, it was later adapted for use with MRI and ultrasound as well.

BIRADS is something that benefits the radiologists who report mammograms (and MRI and US). It doesn't do anything directly useful for patients or for the doctors who referred a patient for breast imaging. What benefit do radiologists get?

The benefit to radiologists, is that it forces them to think about which category their findings will fit into, and when they assign each case into a category, then it becomes possible to calculate accuracy statistics. The accuracy statistics are generally calculated once a year, and they inform the radiologist about whether they are doing a good job, or not. This will re-assure the good radiologists to keep doing whatever they are doing, but for radiologists whose accuracy statistics aren't good, it lets them know that they ought to get more training.

BIRADS classification is not a formal requirement for most radiologists to use, but most do. Another benefit of BIRADS to radiologists, that has indirectly benefitted everyone else, is that the categorization scheme has helped to standardize the words used in mammographic reporting, and this has reduced the confusion and improved communication betweem radiologists, patients, and physicians.

BI-RADS classifcations have also helped in monitoring breast cancer treatment and supporting breast cancer research, again by making statistics easier to calculate.

A woman is usually normally not told of the BI-RADS assessment directly. However, if you do encounter these terms, it may be useful to know what they mean.

BI-RADS mammographic assessment categories

The BI-RADS assessment categories are:

0- incomplete,

1- negative,

2-benign findings,

3-probably benign,

4-suspicious abnormality,

5-highly suspicious of malignancy,

6-known biopsy with proven malignancy.

 

After the initial breast cancer screening, a follow-up or 'diagnostic' mammogram is often recommended when the BI-RADS category was 3 or higher. By a vast majority, most breast cancer screening mammograms are classified as either BI-RADS 1 or BI-RADS 2, and those categories don't imply any further worries.

 

The postive predictive value (for confirmed breast cancer) increases at BI-RADS category 4

Up to 9% of breast cancer screening mammograms will be given a BI-RADS category of 3, 4 or 5, which implies that something needs further concern. It turns out that BIRADS 3 is rarely used nowadays, because BIRADS 4 and 5 are categories that lead to biopsies, and biopsies give "definitive" answers, whereas BIRADS 3 often causes a 6-month follow-up mammogram, which leads to some "uncertainty" for everyone during those 6 months. Both radiologists and patients prefer fast answers rather than waiting 6 months.

If a mammogram is classified into the BI-RADS category 3, it tends to have a very low positive predictive value (less than 2%), meaning a low chance of cancer.

A BI-RADS category 4 mammogram has a positive predictive value of about 30%, and a category 5 mammogram are almost certainly predictive of breast cancer, with a positive predictive value of about 95%.

 

BI-RADS assessment categories:

Category 0 Assemssment is incomplete

Category 0 means the Assessment is not completed yet, and additional workup is often recommended, such as spot compression , magnification, or ultrasound. Category 0 means that there was not enough information yet to finish the process. In real-life terms, if a screening mammogram shows something like a round nodule, and the radiologist thinks it might be a cyst (not cancer), the radiologist will ask for an Ultrasound, and assign a BIRADS 0 category to the mammogram. When the ultrasound result is available, and suppose it showed a benign cyst, then the ultrasound result "completes the BIRADS" and assigns a category 2 to the case, because a cyst is benign.

Category 1. Negative.

With category 1 the breast cancer screening mammogram shows no grouped or suspicious microcalcifications, no well-formed mass, a symmetrical glandular structure, and no change from any previous exam.

Category 2, benign

Category 2 is a definitely benign finding, and a routine screening. That is, something is found, but it is not breast cancer or malignant in any way.

BI-RADS category 2 findings often include:

  1. Round opacities with macrocalcifications (typical calcified fibroadenoma or cyst)
  2. Round opacities corresponding to a typical cyst at ultrasonography
  3. Oval opacities with a radiolucent center
  4. Fatty densities or partially fatty images (lipoma, galactocele, oil cyst, hamartoma )
  5. Surgical scar
  6. Scattered macrocalcifications (fibroadenoma, cyst, cytosteatonecrosis, secretory ductal ectasia);
  7. Vascular calcifications
  8. Breast implants,silicone granuloma.
The specs are benign microcalcifications benign microcalcifications
Here the calcium buildup is in layers, like sediment or leaves in a teacup. layered microcalcifications
Round, benign microcalcification. rounded and benign microcalcification

 

Category 3. Probably Benign

With BI-RADS category 3, a follow-up of 6 months is usually recommended. On the breast cancer screening mammogram there may be a finding of some kind, but the lesion is non-palpable. Findings typical of this category include:

  1. Clusters of tiny calcifications if round or oval
  2. Non-calcified solid nodules (no size limitation but non palpable), round, ovoid, well-defined,
  3. Selected focal asymmetric areas of fibroglandular density (not palpable): This might include concave-outward defined margins, interspersed with fat and without central increased fibular density on two projections.
  4. Miscellaneous focal findings, such as a dilated duct, or post biopsy architectural distortion without central density
  5. Generalized distribution in both breasts. For example, multiple similar lesions with tiny calcifications or nodules distributed randomly

In some scenerios a percutaneous biopsy might be considered,even with category 3. For example, extreme patient anxiety, or plans for pregnancy, plans for breast augmentation or reduction surgery, or if synchronous carcinoma is present.

 

These tiny specs are diffuse punctate microcalcifications. small specs of microcalcifications, probably benign BIRADS 3
This microcalcification is round but the edges are not sharply defined. It would be called 'indeterminate BI-RADS 3 and not BI-RADS 2, because of the poorly defined, fuzzy edge. fuzzy edge round microcalcification

 

The postive predictive value (the chance of having a real breast cancer) is very low for BI-RADS category 3 lesions, and it has actually decreased in recent years. With advances in research and experience, the PPV of a category 3 breast lesions in now considered less than 1%.

Category 4 Suspicious or Indeterminate abnormality

A BI-RADS category 4 mammogram is where the concern for breast cancer begins to increase. A biopsy should be recommended with BI-RADS category 4. Typically, a lesion has been found, but does not initially appear to have the morphological characteristics of breast cancer. BI-RADS category 4 is therefore often subdivided into there smaller sub-categories: "A" for low suspicion of malignancy, "B" for moderate suspicion, and "C" for high suspicion.

Findings typical of BI-RADS category 4 include:

  1. Asymmetric, localized or evolving hyperdensities with convex contours.
  2. Indeterminate microcalcifications appearing amorphous, indistinct particularly if in a cluster or heterogeneous and pleomorphic
  3. Round or oval non cystic opacities with microlobulated or obscured contours

The positive predictive value (the chance of a real cancer) of BI-RADS 4 mammograms, is thought to be in the order of 20-40%.

'powderish microcalcifications are suggestive of BI-RADS classification of 4. powderish clustered microcalcifications, suspicious of malignancy for breast cancer
These 'powderish' microcalcifications appear in large clusters. powerderish microcalcifications, BI-RADS 4

 

BI-RADS category 4C has quite a high positive predictive value for breast cancer

BI-RADS category 4 is now broken in to sub-categories A, B, and C. In terms of the positive predictive value for breast cancer, a category 4A mammogram is quite low at 13%, and category 4B also moderately low at about 36%. But when we see a mammogram classefied as 4C, the positive predictive value of breast cancer jumps up to around 79%.

 

The most common finding in BI-RADS category 4 is breast fibrocystic changes

The exact clinical significance of the subcategorizations of BI-RADS category 4 remains a bit vague. Generally speaking as we move further into categories A,B, and finally C, the chances of the breast lesion being diagnosed as DCIS increases. About 70% of BI-RADS category 4C breast lesions turn out to be ductal carcinoma in situ, while DCIS is found in category 4B lesions only about 21% of the time, and only 10% of the time with category 4A breast lesions. In terms of the frequency of the subcategories of BI-RADS 4, is may be suggested that category 4A is seen about 50% of the time, 4B about 38% of the time, and category 4C only about 13% of the time. The most common confirmed diagnostic finding in BI-RADS category 4, generally, is actually fibrocystic change, at about 28%. DCIS is confirmed about 23% of the time, with columnar cell change and fibroadenoma found in about 19% of cases.

 

Category 5. Highly suggestive of malignancy

A 5 BI-RADS category is assigned when there is a very high probability for breast cancer, and a biopsy should be taken immediately. Finding typical of category five include :

  1. Typically malignant microcalcifications; for example, linear with branching pattern; particularly if numerous, clustered and with a segmental distribution;
  2. Clusters of microcalcifications with a segmental or galactophorous distribution
  3. Evolving microcalcifications or associated with an architectural distortion or opacity
  4. Clusters of microcalcifications with a segmental or galactophorous distribution
  5. Poorly circumscribed opacities with ill-defined and irregular contours;
  6. Spiculated opacities with radio-opaque center.

BI-RADS category 5 is usually reserved for lesions having a 95% probability of malignancy. After biopsy, the average rate of carcinoma in category 5 biopsies is about 75-97%.

  crushed stone casting microcalcifications, very high probability of malignant breast cancer development
  crushed stone probably malignant microcalcifications
Casting microcalcifications appear linear, fragmented, and branching. casting linear fragmented BIRADS 5 microcalcifications highly malignant
In this image the casting microcalcifications are branched, and granular. branched granular microcalcifications

 

Category 6. Known Cancer

Category 6 indicates a known cancer, proven by biopsy. This category is used when patients undergoing breast cancer treatment have follow-up mammograms. For a few years after cancer treatment, category 6 might still be used. Since everyone already knows there is, or was, a cancer, we can't use categories 0 thru 5 anymore, so category 6 is assigned. Category 6 isn't useful for accuracy statistics.

 

Certain microcalcifications might even be 'directly' associated with breast cancer.

BI-RADS mammogram classifications are generalizations only, and tend to revolve around the presence and type of microcalcifications. Within the range of observations about the various types and patterns of breast tissue microcalcifications present, it may be suggested that course heterogenous microcalcifications are positively associated with breast cancer about 7% of the time, and amorphous microcalcifications about 13% of the time. Fine pleomorphic breast microcalcifications have a positive predictive value for breast cancer of about 30%, while fine linear microcalcifications are associated with confirmed breast cancer in over 50% of cases.

 

BI-RADS mammogram classifications are not intended as diagnostic tools, but only a means of standardizing communications and helping to indentify situations where follow-up is required, and the most appropriate type of follow-up. The fastest and most economical way to arrive at a positive or confirmed diagnosis of breast cancer is by core-biopsy.

References

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Copyright Steven B. Halls, MD Last edited 12-September-2011

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