Ultrasound imaging or 'sonography' tends to be used in breast cancer screening as a 'second look' or follow up application. The usual indications for breast ultrasound would be a suspicious finding on mammography or for further diagnostic evalution of a palpable lesion felt on a clinical breast exam. However, just because a woman is sent for a follow up sonogram is no reason to have elevated anxieties about breast cancer. Ultrasound is particularly helpful in distinguishing between a solid mass and a fluid-filled cyst, which is what a majority of breast lesions turn out to be. Ultrasound is also useful in finding very small lesions that are too small to be felt at a clinical exam.
Ultrasound imaging uses high frequency sound waves to form an image, called a 'sonogram'. The sound waves it uses are harmless and pass through the breast and bounce back or 'echo' from various tissues to form a picture of the internal structures. Un unexpected 'echo' means that there is a solid nodule of some kind within the tissue. There is no radiation involved in ultrasound imaging, which makes it a preferred method of diagnostic imaging for pregnant women.
Women with high breast density are often screened with ultrasound, because mammograms of women with dense breast tissue tend to be harder to interpret. For this reason, ultrasound if frequently a 'first' diagnotic imaging method for women under 35. Whether or not an ultrasound can 'stand alone' as a screening method versus combining it with mammography or MRI is still a subject of debate. At present, there is no study which definitively proves that ultrasound screening alone lowers mortality rates for breast cancer, unlike mammography, which does. But a screening mammogram with normal findings, regardless of whether or not a woman has dense breast tissue, is not a reason enough for a diagnostic breast ultrasound.
The combination of ultrasound with Magnetic resonance imaging has been found to be a particularly good combination in followup evaluation of lesions found on mammography. The detail of MRI greatly assists diagnostic and treatment decisions. Ultrasound is also very useful in 'guiding the needle' during a followup biopsy.
The rate at which lesions discovered by screening are shown to be malignant breast cancer is actually very low. The rate of detecting malignancies using mammography (x-ray) is about 5 cancer per 1000 women screened. When ultrasound is used alone to determine malignancy, the rate is slightly lower. This does tend to suggest that mammography is slightly more reliable. But it must be emphasized that even the combination of ultrasound and even MRI with mammography cannot completely exclude the possibility of breast cancer. Up to 3% of women with negative mammograms and sonograms of suspicous lesions may still have breast cancer.
Ultrasound imaging is not really any more expensive than mammography, and in many ways it is more convenient. The problem is, almost all suspicious ultrasound findings are inconclusive and end up being referred for biopsies anyways. This must be weighed against the cost and effectiveness of mammographic screening as a whole, which tends to provide better assurance of the nature of a lesion with respect to the need for a biopsy.
Abnormal results of an ultrasound will tend to fall into four categories. A radiologist can usually tell if the echoes are caused by benign fibrous nodules (breast fibrocystic disease, papillomas, fibroadenomas). Of slightly greater concern are sonographic indications of a 'complex cyst' . The third and fourth informal categories of increased liklihood of malignancy are 'suspicious lesion', and 'lesion highly suggestive of cancer'.
A sonogram gives a good indication of the liquid or solid nature of a lesion, or perhaps a combination. Liquid masses (cysts) tend to be darker in color, and homogenous. An experienced radiologist gains a 'feel' for what the different 'textures' of a sonogram tend to represent. The shape of a lesion and also its 'margin' ( the characteristics of its 'edges' ) are also quite evident on sonograms. This helps determine whether a lesion is cancerous or benign. (Cancerous lesions tend to have jagged edges) Breast cancer lesions also tend to be somewhat random in shape, but not always. Benign fibroadenomas are usually round or oval. But ultrasound is not a definitive test, and tissue analysis via biopsy is usually required. Even when ultrasound suggests the presence of a fibrous nodule or complex cyst, a biopsy is still justified. Up to 15% of these types of growths end up being malignant.
Any ''echoes" on the sonogram ( a change from the sound on its way back compared to on it's way in) indicates that a solid nodule of some kind has blocked the path of the sound wave. Analysis of the solid nodules on a breast sonogram requires considerable expertise, and can give further clarity as to the benign or malignant nature of the lesion.
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