- Author: Muhammad Neaman Siddique, MBBS; Chief Editor: Eugene C Lin, MD more...
Screening versus diagnostic
Diagnostic mammography is performed in women who present with breast symptoms such as nipple discharge or focal pain, who have abnormal clinical findings such as palpable lump, or who have mammographic abnormalities detected on a screening study. It is performed under the direct supervision of a radiologist who chooses different additional views to further demonstrate the morphology of the lesion and decides whether ultrasound also needs to be used. Additional views include cleavage view, tangential view, and rolled view.
Breast implants were approved by US Food and Drug Administration in 1962. Over two million breast implants are estimated to be in US women for the purposes of either cosmetic augmentation or reconstruction.
Women with breast reconstructions with no underlying breast tissue do not require mammographic screening, whereas women with breast augmentations performed with implants do require routine screening to evaluate the native breast tissue. As implant contents are radio-opaque, small lesions may be obscured. Moreover, in patients with breast implants, evaluating all parts of the breast becomes harder because breast compression becomes difficult with implants, particularly in prepectoral or retroglandular implants. Therefore, after obtaining the standard craniocaudal (CC) and mediolateral oblique (MLO) views in women with breast implants, both views are repeated with the implant displaced back against the chest wall and breast tissue pulled forward. Prepectoral or retroglandular implants are sometimes difficult to displace. Tangential views are obtained in such cases, to attempt to adequately image the whole breast tissue.
Postmastectomy myocutaneous breast reconstruction
Mammography of a reconstructed breast is a technically feasible study, and mammographic appearance of recurrences is similar to those in native breasts. Mammography has been found useful in differentiating a true recurrence from post operative fat necrosis that may also present as a lump. However, evidence in favor of routine imaging for asymptomatic women with myocutaneous breast reconstruction is contradictory. Currently, clinical breast examination is the method of choice for screening in these women.
Women with prior breast biopsy
Mammography in women with a history of a prior breast biopsy that diagnosed a benign disease has been shown to have a lower specificity and a lower positive predictive value for a referral for a subsequent breast biopsy compared with women with no history of prior biopsy.
Increased breast density
The presence of dense breast tissue not only poses difficulty in reading the mammogram, but it has been recognized as an independent risk factor for breast cancer. A significant association exists between longitudinal increases or decreases in breast density detected on serial screening mammography and an increased or decreased risk of breast cancer, respectively. Digital mammography has been found out to be more sensitive in women with dense breasts and should be preferred over film mammography to screen these women (see the image below).
Pregnancy and lactation
Breast cancer in pregnant women accounts for 3% of all breast cancers. Mammography is performed in pregnant women for diagnostic purposes only, usually in settings where a sonographic examination is unable to sufficiently clarify physical findings. A mammogram comprising 4 views that is done with abdominal shielding exposes the fetus to 0.4 rads. As fetal exposure to radiation is concerning, especially during the first few weeks of gestation, routine screening mammograms are not performed during pregnancy.
Men undergo mammography to evaluate for a breast mass, thickening, or pain. The initial study comprises of bilateral CC and MLO views, and additional views may subsequently be performed to further elaborate any abnormalities found on standard views. Breast compression is required in men also, and narrower paddles prove more helpful.
Routine mammogram comprises of CC and MLO views. Adequate degree of breast compression is applied before shooting the X-rays. This helps in increasing the image contrast by reducing motion artifact and by enhancing the X-ray penetration. Acquiring 2 views is imperative in order to adequately image the whole breast tissue. Besides this, two views help in distinguishing a true abnormality from an overlapping structure. Studies have clearly established higher sensitivity and lower recall rates with 2 views. This benefit is generally believed to outweigh the risk associated with extra radiation from the second view.
The radiation dose absorbed by the breast depends on breast tissue thickness, increasing with the thickness of the breast. American College of Radiology recommends that the mean radiation dose exposure in a breast tissue measuring 4.2 cm should not exceed 0.3 rads per image. If accounted for the relative sensitivity of breast tissue to radiation exposure, the effective radiation dose received by the breast during a routine screening examination comes out to be approximately equivalent to the natural background radiation exposure cumulatively acquired over a 3-month period (ie, 0.7millisievert units). Women who have BRCA1 or BRCA2 mutation and thus have impaired DNA repair mechanisms are at increased risk for radiation-induced carcinogenesis as compared to women who do not have these mutations. However, keeping the radiation dose as low as possible in all women is important.
A digital mammography system tends to require a lower radiation dose than film screen mammography for the same image quality. Digital detector converts the X-ray photons to an electronic signal, which is further processed and displayed as a gray scale image. This image can either be electronically sent to a viewing station and displayed on a high-resolution monitor or printed and read on luminant-view boxes similar to how the film screen mammograms are read.
The digital system provides greater contrast resolution and thus better visualization of skin, peripheral breast tissue, and dense breasts. Besides this, it allows for changes in zoom, contrast, and brightness, which increase the ability to detect subtle abnormalities.
A film screen system does not offer such facilities and also tends to suffer from artifacts during processing and storage. These deficiencies are, however, partly compensated for by the advantage of a higher spatial resolution in film screens as compared to digital systems. However, despite of all these technological differences, studies have shown that the overall diagnostic accuracy was similar with these 2 modalities except for premenopausal and perimenopausal women in whom digital mammography was found to be more accurate. This is at least partly because digital mammography is relatively more sensitive than film mammography in detecting cancer in dense breasts.
Mammogram identifies abnormal breast tissue as asymmetry, architectural distortion, and calcifications. Calcifications may represent benign or malignant lesions. Linear and branching calcifications have a higher predictive value for malignancy as compared to granular. The most specific mammographic feature of malignancy, however, is a spiculated soft tissue mass; nearly 90% of these lesions represent invasive cancer.
Clustered microcalcifications (calcium particles 0.1-1mm in diameter and numbering more than 4-5 per cubic centimeter) are found in about 60% of mammographically detected cancers. Skin thickening, increased breast density, and coarsening of stroma may be detected in patients with inflammatory breast cancer. Smooth round or oval calcifications, rim-like calcifications, large coarse calcifications, vascular calcifications, cigar or rod-shaped calcifications, multiple coarse "popcorn" calcifications are all considered benign.
Double reading means that the mammogram is read by 2 radiologists either independently or interpreted together. As opposed to the United States, it is a standard practice in Europe. The aim is to increase the sensitivity and specificity of the examination. If the readers happen to differ in their interpretation of a mammogram, the issue can be approached in 3 different ways. Patient may be called back for follow-up studies if either of the radiologists identifies an abnormality, a strategy termed ”highest reader recall.” Alternatively, ”arbitration” is provided by a third reader who reviews the films and determines if the patient needs further diagnostic work-up or a ”consensus” is developed by a panel of radiologists that may or may not include the original readers.
Many observational studies have shown benefit for double reading, but no randomized trials have looked at the practice. Data review from the Norwegian Breast Cancer Screening Program for over a million examinations that were performed by radiologists, 50% of whom were dedicated mammography readers, found that 23.6% of the cancers detected were diagnosed in patients who were recalled for discordant interpretation.
CAD or computer aided detection is a computer-based technology that helps the radiologist in identifying suspicious areas while reading a digitalized mammogram. It was approved by the FDA in 1998. No randomized trials have been performed to assess its effect on breast cancer mortality. A recent meta-analysis showed a small statistically insignificant increase in cancer detection rate, but this was associated with a higher recall rate and more false-positive readings.
Prior to describing the abnormalities, the report gives out the indication for the study, the breast density in percentage, and whether the examination was a screening or a diagnostic procedure.
Abnormalities are reported using the standard Breast Imaging-Reporting and Data System (BI-RADS) descriptors. The location(s) of the lesion(s) are described with reference to a quadrant or clock position, and the depth within the breast. Each breast is arbitrarily divided into 4 quadrants: upper-inner, upper-outer, lower-inner, and lower-outer. In terms of depth, the breast is divided into anterior, middle, or posterior.
After an evaluation is done by the reader, the mammography report is prepared, and all mammograms are labeled as one of the standard BI-RADS categories based upon the presence or absence of various mammographic abnormalities.
The BI-RADS categories are defined as follows:
BI-RADS 0: This means that the assessment is incomplete either because of technical factors, or a lesion is not fully evaluated by the standard screening views, or because prior mammograms are unavailable for confirming stability, or a change in a lesion diagnosed on a prior mammogram. The patient is asked to return for additional mammographic views and/or an ultrasound, or prior mammograms are requested.
BI-RADS 1: This is a completely negative examination. The woman should continue with screening mammography and clinical breast examination based on screening guidelines.
BI-RADS 2: This represents benign findings such as cysts, fibroadenomas, or benign vascular or parenchymal calcifications. Malignancy is not a concern, and routine follow-up is recommended.
BI-RADS 3: This represents findings that do not have characteristic benign features, but the likelihood of malignancy is less than 2%. Examples of such findings are parenchymal asymmetry, calcifications, or a nodule that doesn’t have classic benign imaging features. These patients are advised to have follow-up studies at shorter intervals, during which the category may get upgraded if lesions change sufficiently to raise concern for a malignancy or may get downgraded if repeated imaging confirms benignity of the lesion.
BI-RADS 4: This represents findings that are suspicious for malignancy.
BI-RADS 5: This represents lesions that are highly suggestive for malignancy, such as spiculations, pleomorphic calcifications, and skin retraction.
BI-RADS 6: This represents biopsy-proven malignancy in which the mammogram is being performed to either evaluate the contralateral breast or assess response to neoadjuvant chemotherapy.
Newer Advances: Tomosynthesis
Digital tomosynthesis is a further advancement of digital mammography. A 3-dimensional digital data is acquired with the help of a moving X-ray source and a digital detector and is further processed using computer algorithms to generate thin sections of images. This 3-dimensional reconstruction improves the demarcation of a lesion by reducing the overlap from surrounding structures. Available data suggests that this technique may improve both the sensitivity and specificity of mammographic detection of cancer. However, it requires longer radiation exposure and there remains a concern for increased risk of motion artifact with this technique.
In a British study, in assessing mammographic abnormalities, two-view mammography with one-view digital breast tomosynthesis (DBT) showed significantly higher accuracy compared to two-view mammography and coned compression magnification mammography (CCMM). According to the authors, these results showed that DBT can help evaluate mammographic screening abnormalities.
For further information on digital tomosynthesis see the Medscape Reference topic 3D Mammography.
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