Introduction to BI-RADS for Mammography
The Breast Imaging Reporting and Data System (BI – RADS), introduced by the American College of Radiology in 1992, is now in its fourth edition. This system has been instrumental in standardizing the reporting of mammograms, reducing confusion in image depiction, and monitoring screening.
I. Common Signs
(a) Mass: An occupying lesion seen in two different projection locations with a bulging rim, the rim sign is most important in determining the nature of the mass. A suspicious mass seen in only one projection is called a “dense shadow”; one without obvious bulging edges is called “asymmetric”.
The description of the mass includes three aspects: morphology, margin, and density.
The first three morphologies should be considered in conjunction with other signs.
Margins are most important for diagnosing the nature of the lesion and include the following five descriptions: clear, blurred, lobulated, infiltrated, and asterixis.
Clear margins mean that more than 75% of the mass is clearly and sharply demarcated from the surrounding normal tissue, while the remaining margins may be obscured by the surrounding glands without evidence of malignancy;
Blurred means that the mass is obscured by the normal tissue above or adjacent to the mass and cannot be judged further, usually in cases where the reporter believes that the mass is well defined and only obscured by the surrounding glands;
Small lobules show small wavy changes in the margins;
Infiltration is an irregularity of the border caused by the infiltration of the lesion itself into the surrounding area, rather than by the obscuration of the surrounding glands;
The stellate pattern is seen as a radiolucent shadow emanating from the edge of the mass.
Small lobes, infiltrates and asteroidal margins are signs of malignancy. It is sometimes difficult to distinguish between blurred margins and infiltrates, but it is very important, as the former are mostly benign changes and the latter are malignant signs, which can be helped by localized compression photography and tamponade.
Density is described as high, equal, low (excluding fat density) and fat density compared to the same volume of surrounding breast tissue. Most breast cancers are high or isodense; a very small number of breast cancers may be hypodense; and breast cancers without fat density are benign.
(b) Calcifications: Benign calcifications are usually larger than malignant calcifications, and appear as coarse calcifications or round calcifications with clear edges. Malignant calcifications are often smaller and require magnification to help visualize them. The calcifications are described in terms of both morphology and distribution. Benign calcifications may be left undescribed, but are described when they may be misinterpreted by another physician.
The morphology is divided into typical benign calcifications, intermediate calcifications (suspicious calcifications), and calcifications of high malignancy potential.
Typical benign calcifications have the following 10 typical presentations.
The skin calcification is coarse and typical with translucent changes in the center; atypical calcifications can be identified with the help of cut line projection;
Vascular calcification is tubular or track-like;
Rough or popcorn-like calcifications are often larger than 2 – 3 mm in diameter and are characteristic of fibroadenoma calcifications;
Coarse rod-like calcifications are continuous, rod-like, occasionally branching, usually larger than 1 mm in diameter, and may have a central translucent change with a well-defined margin, distributed along the ducts and clustered towards the nipples, often bilaterally, and most often seen in secretory lesions;
Round and punctate calcifications, less than 1 mm or even 0.5 mm, are often located in lobular follicles, and clusters are a cause for alarm;
”Ring” or “eggshell calcifications” with thin walls, often less than 1 mm, are calcifications deposited on the surface of spherical objects and are seen as fatty necrosis or cysts;
Hollow calcifications can range in size from 1 mm to 1 cm or even larger, with smooth rounded or ovoid edges and a central hypodense wall that is thicker than the “ring” or “eggshell” calcifications. adenoma;
Milk-like calcifications are intracystic calcifications that are not obvious in the cephalopod axis (CC), are villi-like or indeterminate in shape, are well defined in the 90° lateral view, and are semilunar, crescentic, curvilinear or linear depending on the morphology of the cyst, and are characterized by changes in morphology with body position;
Suture calcification is due to calcium deposition on the suture material, especially after radiotherapy, and is typically linear or tubular in shape, with knot-like changes often seen;
Dystrophic calcification is often seen in the breast after radiotherapy or trauma, with irregular calcification patterns, mostly larger than 0.5 mm, with hollow changes.
Intermediate calcification (suspicious calcification) includes two types of calcification: indefinite fuzzy calcification and rough inhomogeneous calcification.
Indeterminate fuzzy calcifications: they are often small and fuzzy without typical features, and their diffuse distribution is often benign.
Coarse, inhomogeneous calcifications: most are greater than 0.5 mm and may be malignant, but can also occur in benign fibrosis, fibroadenoma, and post-traumatic breast and need to be considered in conjunction with distribution.
Calcifications with a high malignant potential can also take two forms, small polymorphic calcifications (granular punctate calcifications) and linear or linear branching calcifications (cast calcifications).
Granular punctate calcification is more suspicious than indeterminate calcification and varies in size and shape, often less than 0.5 mm in diameter.
Linear branching calcifications appear as thin, irregular lines, often discontinuous and less than 0.5 mm in diameter, which suggest that the calcification is formed from the lumen of the duct invaded by breast cancer.
Highly malignant calcifications may be characterized by heterogeneity, including morphology, size, and density.
The distribution of calcifications is often helpful in indicating the type of pathology of the breast lesion and includes the following five distribution patterns.
Diffuse or scattered distribution refers to calcifications that are randomly scattered throughout the breast, with punctate and pleomorphic calcifications being benign and often bilateral;
The nature of this distribution needs to be considered in conjunction with the morphology;
A clustered distribution is defined as at least 5 calcifications occupying a small space (< 2cm × 2cm × 2cm) and can be present in both benign and malignant lesions;
A linear distribution of calcifications in a linear pattern, with branching points visible, suggests a ductal origin and is often malignant;
Although benign secretory lesions may also have segmental calcifications, if the morphology of the calcifications is not characteristically benign, malignant calcifications should be considered first.
(iii) Structural distortion: This refers to distortion of normal structures without clear mass visibility, including radiolucency and focal constriction from a single point, or distortion at the edge of the parenchyma. Structural distortion can also be a concomitant sign of a mass, asymmetric densities, or calcifications. In the absence of a history of local surgery or trauma, structural distortion may be a sign of malignant or radiolucent scarring and should be referred for clinical excisional biopsy.
II. Special signs
(i) Asymmetrical tubular structures/single dilated duct: tubular or branching structures may represent dilated or thickened ducts. It is of little significance if not accompanied by other suspicious clinical or imaging signs.
(ii) Intramammary lymph nodes: typically kidney-shaped, with translucent cut marks due to fat in the lymph node portal, often less than 1 cm; when the lymph nodes are large, but the majority of them are fatty, they are still benign. There may be multiple lymph nodes, or a single lymph node may look like multiple round nodules due to significant fat replacement. The diagnosis can be made correctly for characteristic changes in the upper outer breast. Occasionally, they may be found in other areas.
(iii) Glomerular asymmetry: This can be determined by comparison with the contralateral breast tissue, which is larger and at least one quadrant in extent. It consists of a larger breast tissue that is denser than normal breast tissue or has more visible ducts, no focal mass formation, no structural distortion, and no accompanying calcifications. It often represents a normal variant, or the result of hormone replacement therapy. However, it may be clinically significant when it coincides with clinical palpable asymmetry.
(iv) Focal asymmetry: A dense change that cannot be accurately described by other shapes. It is shown in both projection locations, but lacks the marginal changes characteristic of a true mass and is less extensive than a mass asymmetry. It may represent a normal breast island, especially if it contains fat. However, because it lacks characteristic benign signs, it often requires further examination, which may reveal a true mass or significant structural distortion.
Combined signs
These are often combined with masses or calcifications, or as separate changes without other abnormalities. These include skin indentation, nipple depression, skin thickening, trabecular thickening, skin lesions projected in the breast tissue, axillary lymph node enlargement, structural distortion, and calcification.
Overall assessment
I. The assessment is incomplete
Grade 0: Additional imaging is required for further evaluation or comparison with the anterior film. Often used in the setting of screening, but rarely after complete imaging and comparison with the anterior radiograph. Other imaging methods recommended include local compression photography, magnification photography, special projection posture photography, and ultrasound.
Second, the assessment is complete
(i) Grade 1: Negative. No abnormal findings.
(ii) Grade 2: benign findings. These include calcified fibroadenomas , multiple secretory calcifications, fat-containing lesions (lipid cysts, lipomas, ductal cysts and mixed density mismatched tumors), intramammary lymph nodes, vascular calcifications, implants, structural distortions with a history of surgery, etc. In general, there are no signs of malignancy on x-ray.
(iii) Grade 3: Possible benign findings, short-term follow-up recommended. There is a high probability of benign findings, and it is expected that the lesion will stabilize or shrink during short-term (less than 1 year, usually 6 months) follow-up to confirm the determination. The malignancy rate at this level is generally less than 2%. The three signs of a well-defined mass without calcification, focal asymmetry, and clustered round or/and punctate calcifications are considered to have a high probability of benign changes. For this level of management, a short-term follow-up of radiographs (6 months), followed by 6 months and 12 months of follow-up to 2 years or more of stability, is used to confirm his determination. 2 or 3 years of stability may change the original grade 3 reading (probably benign) to a grade 2 reading (benign). This grade is used after a complete imaging evaluation and is generally not recommended for initial screening; it is also inappropriate for the evaluation of clinically detected masses; biopsy should be recommended rather than continued follow-up for lesions that appear to be benign and increase in size during follow-up.
(iv) Grade 4: suspicious abnormality, biopsy should be considered. This level includes a large group of lesions requiring clinical intervention, which do not have characteristic morphological changes of breast cancer, but have the possibility of malignancy, with an overall malignancy rate of about 30%. This group is further divided into 4A, 4B, and 4C, where clinicians and patients can make a final decision on the management of the lesions according to their different malignant potential.
1. 4A: This includes a group of lesions that require biopsy but have a low malignant potential. Results that are benign on biopsy or cytology can be relied upon and can be followed up routinely or after 6 months. Substantial palpable masses with well-defined margins on X-ray that are suggestive of fibroadenoma on ultrasound, complex palpable cysts, and palpable abscesses are included in this subclass.
2. 4B: Moderate malignancy is possible. It is important for radiologists and pathologists to agree on the credibility of puncture biopsy results in this group of lesions. Partially well-defined, partially infiltrated masses with fibroadenoma or fat necrosis on puncture are acceptable and are followed up. In the case of papillary tumors, further excisional biopsy is required to confirm the findings.
3. 4C: A group of lesions that are further suspected to be malignant, but not yet typical of grade 5. Irregularly shaped parenchymal masses with infiltrating margins and clusters of small pleomorphic calcifications may be included in this subgrade. Those with grade 4 images, regardless of subgrade, should be followed up regularly after benign pathologic findings. In the case of grade 4C images with benign pathological findings on puncture, further evaluation of the pathological findings should be performed to clarify the diagnosis.
(v) Grade 5: Highly suspicious of malignancy, and appropriate clinical measures should be taken (almost certain malignancy). This type of lesion has a high probability of malignancy. The probability of detecting malignancy is greater than or equal to 95%. High-density masses with irregular awning margins, segmental and linear distribution of small linear and branching calcifications, and irregular awning margins with polymorphic calcifications should be included in this class.
(vi) Grade 6: Biopsy confirmed malignancy and appropriate measures should be taken. This grade is used for imaging evaluation of biopsy-confirmed malignancy that has not yet been treated. The main purpose is to evaluate imaging changes after prior biopsy or to monitor imaging changes from neoadjuvant chemotherapy prior to surgery.