Breast Ultrasound Lesion Assessment BIRADS: Ultrasound - SD

Introduction

Hi, I am Dr. Christopher Merritt, professor of radiology at Thomas Jefferson University in Philadelphia.

For a number of years, the ACR Lexicon for mammography BI-RADS has been an essential part of the interpretation and reporting of mammographic studies.

Recently, a lexicon for the description of sonographic features of masses within the breast has been created by the American College of Radiology.

BI-RADS ultrasound and my presentation will deal with a description of the BI-RADS lexicon and its application to the characterization of breast masses.

Background and Rationale

For a number of years, the ACR BI-RADS Lexicon has been used to assist mammographers in describing the mammographic features of breast lesions.

Recently, a lexicon for the description of breast ultrasound features has been created by the American College of Radiology, BI-RADS ultrasound.

This is an important addition in view of the growing use of ultrasound as a complement to mammography in the evaluation of breast lesions.

The rationale for the development of the lexicon is based on the fact that up to 10% of patients referred for mammography have masses which may be found to benefit from ultrasound evaluation.

Lesion features shown with ultrasound may be used.

Therefore, to formulate a combined assessment category and management recommendation, the BI-RADS lexicon forms a basis from which these descriptors and assessment categories may be derived.

Indications for Breast Ultrasound

Currently, the indications for breast ultrasound include the evaluation of equivocal masses noted on mammography.

In this case, the large masses seen in the subareolar region on evaluation.

This was initially felt to be a cyst and aspiration was performed returning a large amount of cyst fluid after aspiration, however, a small mass was still felt.

For this reason, ultrasound was performed.

The ultrasound shows in addition to the partially drained cyst, a solid mass with features suspicious for cancer biopsy confirmed a high grade breast cancer.

Another indication for a breast ultrasound is in the evaluation of palpable masses in young women less than 30 years of age.

In this case, the palpable lesion shows benign features and upon biopsy was proven to be a benign fibroadenoma.

When biopsy is indicated, ultrasound is perhaps the most convenient and rapid means of providing localization for needle biopsy of breast masses, and this remains an important practical application of breast ultrasound.

Ultrasound is also used in the evaluation of breast implants and may complement magnetic resonance imaging and other methods in the assessment of implant rupture.

Development and Purpose of the BI-RADS Ultrasound Lexicon

The breast imaging reporting and data system now includes a lexicon for the description of not only mammographic features, but ultrasound and breast MRI imaging.

The ultrasound lexicon was developed by a team including Dr. Ellen Mendelson, Janet Baum, Wendy Berg, Christopher Merritt, and Ava Green.

The lexicon is intended to assist users in applying standardized descriptors to characterize and report sonographic findings of breast pathology.

The combined mammographic and ultrasound reports are then intended to lead to the assignment of an assessment category and appropriate management recommendation.

The lexicon incorporates terms to describe important diagnostic features of breast lesions.

These include the size, shape, margin, features, orientation, and attenuation characteristics of a mass.

In addition, the lexicon includes descriptors of the architectural pattern and fibroglandular echogenicity and fat echogenicity.

Diagnostic features also include indirect signs that may be associated with cancers, including changes in the Cooper's ligaments, calcifications, skin thickness, and ductal alterations.

Breast pathology encompasses a broad range of benign as well as malignant lesions.

Benign lesions include simple cysts, skin lesions, dilated ducts, intramammary, lymph nodes, foreign bodies, including silicones and edema.

Criteria for Benign Lesions

Over the years, a number of criteria have been established to aid in the identification of benign lesions.

That is masses with a less than 2% risk of malignancy.

These include an ovoid shape, the presence of two or three, gentle lobulation, circumscribed, linear and well-defined margins, homogeneous echo texture, edge shadowing, and orientation of the long axis of the mass parallel to the skin, distal acoustical enhancement lesions that are uniformly hyperechoic relative to fat and the absence of any suspicious features.

Features Associated with Malignant Lesions

Features associated with malignant lesions include irregular shapes, poorly defined margins, central shadowing, architectural distortion, and orientation of the long axis of the lesion parallel to the skin, as well as heterogeneous echo texture.

The BI-RADS ultrasound lexicon includes specific terms to describe many of these features, including the background, echo texture, numerous features of the mass, as well as changes in surrounding tissues, calcifications and vascularity.

Key Descriptors in the BI-RADS Ultrasound Lexicon

Background Echo Texture

Background echo texture should be described as homogeneous or heterogeneous, and if homogeneous, the predominant pattern of fat or fibro tissue is included.

In this example, the background is homogeneous and it's composed primarily of fat.

In this example, a homogeneous background composed of fibroglandular tissue is present, and in this example, the background is heterogeneous composed of a mixture of fatty and fibroglandular elements.

Mass Characteristics

The most important characteristics in terms relate to the mass identified with ultrasound within the breast.

A mass is defined as a space occupying lesion, which is visible in two different projections.

Masses must be distinguished from normal structures such as ribs or fat lobules using two or more projections as well as real time scanning.

Shape

The first characteristic of the mass that should be described as the shape and the lexicon includes three descriptors, oval, round, and irregular.

An oval mass is elliptical or egg shaped.

This includes masses that have two or three gentle undulations or lobulation.

In this example, a typical benign oval mass is shown a benign fibroadenoma.

Here transverse incidental views of an additional mass with oval shape.

Also a fibroadenoma.

A round mass is spherical, ball shaped circular or globular with an anterior, posterior, and transverse diameters, which are equal round lesions include cysts shown on the top as well as the homogeneous small cancer shown in the bottom pair of images.

If a mass is neither round nor oval, it should be described as irregular.

This feature is highly suspicious for many cancers.

In this case, a small mass is seen in two views.

It can neither be described as oval or round, and therefore should be described as irregular.

This proved to be a small invasive cancer.

Orientation

Next to be described as the orientation of the mass with respect to the skin.

The options here are a mass which is parallel to the skin and one which is not parallel.

Lesions that are not parallel to the skin may also be described as taller than wide, and this includes lesions which are round or spherical.

Here are examples of parallel, not parallel.

Lesions are shown an intramammary lymph node on the left, which is parallel to the scan and a small cancer, which is not parallel in the right.

Here.

Another example of an invasive cancer in which the long axis is perpendicular rather than parallel to the skin.

Margin

The next feature to be described is the margin of the mass.

This is the edge or border of the lesion.

A number of descriptions may be used to describe mass margins, and these are generally ranked in the order of increasing correlation with malignancy.

Often lesions will have several margin characteristics, in which case the descriptor with the highest suspicion for malignancy should be selected.

Margins may be circumscribed or not circumscribed, in which case they may be described by a variety of terms including indistinct, angular, microlobulated or spiculated.

Circumscribed margins are well-defined sharp with an abrupt transition between the lesion and the surrounding tissues.

As is shown in this example of a simple cyst.

Most of these lesions with circumscribed margins also have round or oval shapes.

Here's a fibroadenoma, which shows a circumscribed margin sharply defining the mass from the surrounding breast tissue on the left and a smaller lesion.

Also fibroadenoma showing similar features on the right.

If the mass is not circumscribed, it may consist of one or more of the descriptors, including indistinct, angular, microlobulated, or spiculated.

In this example, an irregular hypoechoic mass, which is not parallel is seen.

However, the delineation of the mass from the surrounding normal breast tissue is extremely difficult to define and is indistinct.

Here are additional examples of lesions with indistinct margins.

Each of these represents an invasive cancer.

In this example, the margin is indistinct, but also shows clear cut areas of angulation and spiculation, which would be additional terms applied to the indistinct descriptor, and here another cancer also showing extensive irregularity with spiculation around the margins.

This finding often indicating the presence of invasion of the cancer into the surrounding soft tissue.

Boundary

In addition to the margin, often a lesion boundary is visible.

This is the transition zone between the mass and the surrounding tissue.

This boundary may result in an abrupt interface between the lesion and the surrounding tissue, or may consist of an echogenic halo in which there's no sharp demarcation between the mass and the surrounding tissue, but with an echogenic zone of transition.

This is often associated with carcinoma and also may be seen with abscesses.

Here we see the comparison of a lesion with a sharp lesion boundary well-defined on the left and an echogenic halo surrounding the cancer on the right.

Again, a cyst with an abrupt boundary and two cancers showing echogenic halo surrounding irregular hypoechoic masses, each of which contains spiculations and micro.

Echo Pattern

Another characteristic described is the echo pattern of the lesion.

This may be anechoic without any internal echoes, as is typical with a simple cyst hyperechoic relative to the fat and equal to the fibroglandular tissue complex containing both anechoic and echogenic components, hypoechoic relative to fat with low level internal echoes or isoechoic showing the same echogenicity as fat.

Several of these patterns are shown in this panel.

The image on the left being anechoic and representing a small cyst, the one in the center being hyperechoic consisting of the echogenic hilum of an intramammary lymph node and the mass on the right being hypoechoic and representing a small ductal carcinoma.

With proper gain settings.

The cyst should be completely anechoic and when these features are present, ultrasound is extremely accurate in the definitive diagnosis of cysts.

Each lesion with increased echogenicity compared to fat is shown resulting in a classification as hyperechoic, and in this example, both cystic and solid elements are present resulting in a complex description of the echo quality.

Occasionally lesions are very similar in their echogenicity to the surrounding fat.

In this case, the lesion is isoechoic, and here an example of a hypoechoic lesion with low level internal echoes.

Again, it is extremely important to be sure that proper gain settings and focal zone placement are used to be certain that low level echoes are displayed in solid lesions and that low level echoes representing artifact are not displayed in cystic lesions.

Posterior Acoustic Features

Posterior acoustic features represent the attenuation characteristics of the mass with respect to acoustic transmission.

Lesions may show no posterior acoustic features, or they may show enhancement with increased posterior echoes or shadowing with decreased posterior echoes, or they may show a combination of both shadowing and enhancement.

On the left, a small lesion is seen without any acoustic features in the middle, typical enhancement with cyst and on the right shadowing associated with a cancer.

Here are additional examples of lesions with no posterior acoustic features.

The one on the left being a small fibroadenoma, the one on the right being a small cyst in the case of the cyst shown on the right compound imaging was used to produce this image.

Spatial compounding may result in diminution of the conspicuity of both enhancement and shadowing and accounts for the relative lack of enhancement in this image.

Here are a more typical example of enhancement associated with cyst as shown, and in this case rather pronounced shadowing, perhaps even more conspicuous than the lesion itself is seen in association with a small cancer.

In this example, careful inspection shows both scattered areas of enhancement as well as shadowing, representing a combined pattern also related to an invasive cancer.

Associated Features

Lesions may be associated with changes in the surrounding soft tissues.

These include compression of tissue around the mass obliteration of tissue planes, changes in Cooper's ligaments, the echogenic halo, which has been described in the boundary descriptors and edema.

Ducts may be shown to have abnormal caliber or branching.

Cooper's ligaments may show straightening or thickening and increased echogenicity in surrounding tissue or reticulation of the tissue may be seen in association with edema.

Architectural disruption of normal anatomic planes is often seen with cancers and occasionally skin thickening, either focal or diffuse indicated by thickness of skin greater than two millimeters except in the periareolar area, as well as occasional skin retraction and irregularity.

Here, an intraductal mass, an intraductal papilloma is seen within a dilated duct.

In this example, there is distortion of the Cooper ligaments caused by desmoplastic reaction due to the underlying invasive cancer,

The Cooper ligaments are contracted and drawn into the area of the tumor.

In this example, a subtle mass erupts the Cooper ligament, which suddenly disappears in the middle of each image, at the location of the mass.

In this case, architectural distortion is evident by the disruption of the Cooper ligaments as well as the change in the orientation of the Cooper ligaments as they approach the invasive cancer.

And another example showing similar findings with distortion and displacement of the Cooper ligaments.

In this case, skin thickening greater than two millimeters is associated with an invasive cancer.

Calcifications

Ultrasound is not ordinarily viewed as an effective means to evaluate the breast for calcifications.

However, when areas of calcification are seen mammographically, they can often be localized and identified with ultrasound.

Calcifications may be described in terms of their size with macrocalcifications applied as a term to be used.

When calcifications are more than a half a millimeter in diameter, these are often coarse and will attenuate sound causing shadowing and are commonly seen in fibroadenomas,

microcalcifications, or calcifications.

Less than a half a millimeter in size may be seen within masses or may be seen outside of masses, in which case they may be less conspicuous.

This panel shows three patterns of microcalcifications on the left, of course, calcification with shadowing associated with a fibroadenoma and the center microcalcifications in this case also associated with a fibroadenoma and on the right subtle calcifications, not associated with a mass.

Here, a typical intraductal carcinoma with microcalcifications is seen, and here subtle findings of calcifications without a mass is seen corresponding to an area of abnormality noted on a mammogram.

This example shows several small microcalcifications within a mass corresponding to those shown in the specimen radiograph on the right.

Unique Findings

In addition to these findings which are commonly seen with breast lesions, a number of unique findings are occasionally noted.

These include clustered microcysts without a discreet solid component.

Complicated cysts, which may contain mobile internal echoes and or fluid debris levels masses within the skin, including sebaceous or epidermal inclusion cysts, foreign bodies including silicone clips, wires, catheters, and so forth, intramammary lymph nodes, and axillary lymph nodes.

Vascularity

Finally, the BI-RADS ultrasound lexicon comments on descriptors to describe vascularity within a mass vascularity is normally compared with the contralateral breast in a similar location or within the same breast in an area of normal tissue.

Comparing the vascularity of the mass with the reference Tissue Descriptors for vascularity include none, no flow seen with color imaging flow within the lesion flow immediately adjacent to a lesion or generally increased flow in the surrounding tissue.

Reporting and Assessment

The BI-RADS lexicon includes not only description of the features of masses and appropriate terms to be used to describe these features, but also comments on how these terms should be used to generate a final assessment and management recommendation.

The report of the ultrasound finding should reference the clinical history, prior studies if available or pertinent.

The studies imaged and evaluated the types of other imaging studies that are included in the overall assessment.

Most often this will be mammography, but may include correlation with other imaging studies such as MRI, concluding with an overall assessment category and appropriate management recommendation.

The description of the lesion should be in accord with the lexicon indicating the type of breast tissue in the area of concern.

The lesion size measured in at least two dimensions, the location of the lesion using a consistent and reproducible system and a concise characterization of the lesion using the BI-RADS descriptors.

The Ultrasound findings should then be used in conjunction with the mammographic and or MRI findings to determine a final assessment.

The overall assessment and recommendation management should reflect the most suspicious features of the studies performed.

Final assessment coding is in accord with the BI-RADS approach.

A code zero indicates an incomplete study which requires additional imaging evaluation.

BI-RADS one is a negative study with no findings, warranting routine follow-up for the patient's age.

BI-RADS category two is a benign finding, also resulting in routine follow-up.

For the patient's age, a BI-RADS three code is assigned to a lesion which is probably benign, however, short term, usually six month follow-up should occur.

In these cases, more suspicious lesions include BI-RADS four lesions and BI-RADS five lesions, which have varying degrees of increasing suspicion for malignancy.

In each of these cases, tissue sampling with biopsy is required.

Summary

In summary, the BI-RADS ultrasound lexicon has become an important adjunct to the BI-RADS lexicon for mammography in the evaluation of patients with breast lesions and in the increasing use of ultrasound to complement mammography and this evaluation.