Ultrasound is a useful diagnostic tool for breast cancer, especially for younger patients. Most of the time breast ultrasound is used as a way to distinguish solid from cystic masses and often to determine the extent of cancer in known or suspected cases. For young women (younger than 30) ultrasound imaging may be the first step which a clinical exam reveals either a palpable mass or nipple discharge. (Since breast cancer tends to happen with older post-menopausal women, doctors try not to expose younger women to the unneccesary radiation of a mammogram). But sonography can help establish the differentiation between benign and malignant solid tumors as well. A lack of circumscribed margins, heterogeneous echo patterns, and an increased anteroposterior dimension can indicate a higher probability of malignancy in solid breast nodules.
The most important features on a breast ultrasound are the clarity and contour of the mass margins, the orientation and shape of the mass, the echo texture and echogenecity, and the effects on distal echoes. Others aspects of the mass such as compressibility and vascularity may also be noted. Some of the features one might usually find in a sonograph of a malignant breast mass would include a marked hypoechogenecity, acoustic shadowing, a branch pattern or microlobulation, or a duct extension. Other malignant features might be a 'taller than wide' shape, angular margins, the presence of calcifications, and spiculation, which probably has the highest positive predictive value for malignant breast cancer. Benign breast lesions on the other hand tend to appear on ultrasound with intense and uniform hyperechogenecity, as an oval shape with a thin, consistent capsule, and they may have two to three gentle lobulations.
A breast sonograph can help in diagnosis in differentiating between benign and malignant tumors, often without the need for a biopsy. The absence of a well-circumscribed margin, heterogenous echo patterns, as well as an increased aneteroposterior dimension to the imagel does tend to indicate a higher probablity of malignant cancer in solid breast nodules. A BI-RADS classification of 3, which means 'probably benign' and with recommended short term follow up only, can only be given if there is an absence of any of these clearly suspicious features.
|Sonographic characteristics||Benign||Potentially Malignant|
|Absence of malignant findings||x|
|Hyperechoic/ intense, fibrous tissue like||x|
|Two or three macrolobulations||x|
|Ellipsoid shape/ wider than tall, parallel to the skin||x|
|Pseudocapsule/ thin, echogenic, well-circumscribed||x|
|Spiculations/ alternating hyper and hypoechoic straight lines||x|
|Height/ width >1 or non parallel to the skin||x|
|Shadowing/ through transmission attenuated||x|
|Branch pattern extensions / multiple radial projections, peri or intra-ductal, nipple oriented||x|
|Markedly hypoechoic ..||x|
|Duct extension / single radial projection, peri or intra-ductal, nipple oriented||x|
|Intracystic nodule*, parietal thickening*||x|
The most typical sonographic presentation of a malignant breast mass would probably be an irregular, heterogenoush, hypoechoic mass, with spiculations and angular margins. And, these kinds of masses tend to have that 'taller-than-wide' appearance, and also demonstrate acoustic shadowing. The image below shows an ill-defined border, an irregular shape, microlobulations, and spiculations (which appears as a hyperechoic 'band' around the mass). The lesion also appears to be 'taller-than-wide', with an angular margin. This would all be highly predictive of invasive ductal carcinoma, and the lesions would be biopsied.
Spiculations often represent breast tumor 'tentacles' or desmoplastic reactions. On ultrasound, spiculations will often consist of straight lines that 'radiate' in a perpendicular fashion from the surface of the breast mass.
An 'angular margin' is observed as an angular configuration ot the junction between relatively hypoechoic or isoechoic central portion of a solid mass and surrounding tissue. Sometimes these features are referred to as 'jagged' or 'irregular' margins. Angular margins are quite distinct from 'lobulations' which tend to be smooth and rounded. Angular margins observed on breast ultrasound are highly predictive of malignancy.
If a solid breast nodule appears on ultrasound to be 'taller-than-wide', this is quite suspicious of malignancy. When a patient is scanned by ultrasound, they are usually in a supine position, and as a result the normal 'tissue planes' on the breast will have a horizontal orientation. If a mass or part of the mass seems longer in the anteposterior dimension (tallness) compared to either the sagittal or transverse dimensions (depth and width) then one can conceive that this might likely be caused by a malignancy 'aggressive enough' to overcome normal breast tissue barriers and planes, and grow vertically.
Hypoechoic breast lesions are suspcious for malignancy, and on ultrasound imaging they will tend to look inensely black compared to the surrounding isochechoic fat. But malignancies can also be isoechoic and hyperechoic on breast ultrasound, so it is not a 'hard and fast' finding by any means.
'Microlobulations' observed on breast ultrasound indicate the presence of lots of very small (1mm to 2 mm) lobulations on the surface of a solid breast nodule, and will be quite similar to mammogram findings. As the number of these microlobulations increase, the probability that the breast mass is malignant also increases.
A 'duct extension' is appears on ultrasound as a 'radially oriented' projection that seems to arise from the lesions an axis oriented towards the nipple. These projections are often observed both within or around breast duct. Sometimes a duct extensions/projection can be observed which has developed as a 'bridge' between multifocal malignancies. This is different from a 'branch pattern' in which multiple extensions are seen to arise from the mass but extend away-from the nipple. A branching pattern tends to indicate a tumor growth advancing away from the nipple. Any apparent growth that is long enough to visibly fill a duct and branch, no matter what direction is goes, will be suspicious for malignancy and be biopsied.
If a breast lesion shows posterior acoustic shadowing on ultrasound this means that there is something about the mass or around the mass which attenuates (reduces) the sonic beam strength when compared to normal adjacent tissues. Posterior acoustic shadowing is suspicious for malignancy, but tends to be associated with low to intermediate grade breast tumors. What may be happening is that a slow growing breast tumor causes a secondary 'desmoplastic response' in the surrounding tissue. That means that dense fibrous and connective tissues are growing around the tumor as a kind of defense mechanism by the body; to 'contain' the neoplastic growth. High grade malignancies in the breast grow too fast for this desmoplastic reaction to occur. However, posterior acoustic shadowing caused by a desmoplastic reaction can be found in benign breast neoplasms as well. For example, fibrosis inside a tumor can block ultrasound from passing deeper, causing acoustic shadowing. But most benign tumors do not usually shadow unless they are calcified. A biopsy will likely be required.
Mammography is more sensitive than ultrasound when it comes to the detection of microcalcifications. Calcifications on a solid mass which appear 'punctate' are highly suspicious of malignancy, and will usually appear on ultrasound as bright, punctate foci. Since malignant breast lesions are typically either intensely or mildy homogenous hypochoic solid masses, on ultrasound this provides a 'background' which makes it easier to view calcifications sonographically. So, while calcifications are usually not seen on ultrasound, when they do appear vividly, it is highly suspicious for malignancy
In terms of the suggested 'BI-RADS' descriptors for malignant breast nodules, spiculated margins have a positive predictive value for malignant breast cancer in about the 85% range. Masses showing an irregular shape or non-parallel orientation are also quite suggestive of malignancy, with a positive predictive value in the 62% to 69% range. Other studies place a higher predictive value on the presence of an irregular border (about 88% predictive of malignancy) and evidence of increased vascularity in the mass predicts maligancy about 82% of the time. The sonograph image below shows an irregular vascularized retroareolar mass, with calcifications. This is very likely to be infiltrating ductal carcinoma and a biopsy sample would likely be taken right away.
On ultrasound, a benign breast mass will typically be well defined and with smooth margins. The lesion might also be macrolobulated or with just 2 to 4 mild lobulations. Benign breast lesions also tend to be ovoid or round in shape, and are often 'wider-than-tall' (which indicates a parallel orientation to the chest wall). The echo texture of a benign mass will usually be homogeneous with an isoechoic, hyperechoic, to mildly hypoechoic echogenicity. Some benign breast masses will also exhibit mild acoustic enhancement on ultrasound, and might be slightly compressible. Vascularity in an ultrasound of a benign mass is variable and will depend on the specific histology of the suspecious mass.
In terms of sonographic features suggestive of benign breast lesions, a well circumscribed margin has a positive predictive value for being benign about 90% of the time, and an 'oval shape' about 84% of the time. Breast lesions with a 'parallel' orientation are predictive of benignity almost 80% of the time.
The quality of the margins of a breast lesions scanned with ultrasound are is sometimes referred to as its 'capsule'. If the margin of the suspected mass seems well-circumscribed in both it's inner and outer edges, and seems thin and even, this tends to be a sign of a benign mass. The lesion is 'encapsulated' by the compressed adjacent breast tissue, and the mass itself is 'pushing against' this tissue, rather than infiltrating and invading that tissue.
Sometimes you do see a mild undulation in contour on ultraound with a benign fibroadenoma. But there should not be many of these mild 'lobulations', and usually any more than three is considered a potentially malignant sign. Of greater concern are more numerous, smaller, and sharper microlobulations than one tends to find in malignant breast cancer tumors.
Breast lesions which appear as having a marked and uniform hyperechogenicity are highly predictive of a benign lesion. This feature typically represents normal fibrous changes within the breast. But when there are some regions are either hypechogenecity or isoechogenecity that are larger than normal (larger than either normal ducts or terminal ductal-lobular units) , that would indicate a 'medium' level of concern and would probably result in a biopsy, particularly if these areas were not contained within fat lobules.
The 'compressibility' of a breast lesions scanned with ultrasound refers to changes in the shape of a lesion as a result of the pressure applied by the probe. A solid, likely malignant, breast lesion will not 'compress' at all from the pressure of the probe, but a tumor of benign fibrous or glandular tissue, such as a fibroadenoma, will show some compressibility. A benign breast fibroadenoma is usually oriented horizontally, more wide than tall. Often the compression of the scanner will cause a 'flattened' oval shape of a fibroadenoma, which would not occur with solid, malignant breast lesions.
Sometimes a breast ultrasound will pick up an enlarged node in axilla. Many breast cancer oncologists would take an enlarged axillary node on ultrasound as proof positive for lymph node metastasis, even without a lymph node dissection. (Sometimes patients will not agree to a lymph node dissection to check for breast cancer metastasis)
If the findings of ultrasound imaging of suspicious breast nodules where expressed as an odds ratio ( the odds of a person with these features as having breast cancer, as compared to an breast ultrasound where these features are not present) it may be suggested that breast lesions without a well-circumscribed margins are almost 17x more likley to indicate malignant breast cancer. Breast sonographs showing a heterogenous echo texture are about 8x more likely to be breast cancer. The 'incompressibility' of a breast lesion on ultrasound would tend to be almost 9x more likely to be malignant.
Not all suspicious breast lesions will be straightforward in their ultrasound appearance and diagnosis. In some cases the findings are still inconclusive, with a recommendation for short interval follow-up, or biopsy. But, one of the reasons to use ultrasound in the first place is because there is a high suspicion of a benign mass to begin with, and the use of ultrasound is mostly to confirm the cystic nature of the lesion. For example, ultrasound can not always reliably confirm the diagnosis of a breast abscess.
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