Mammography is the standard of reference for the detection of breast carcinoma, yet 10%-30% of breast cancers may be missed at mammography. Possible causes for missed breast cancers include dense parenchyma obscuring a lesion, poor positioning or technique, perception error, incorrect interpretation of a suspect finding, subtle features of malignancy, and slow growth of a lesion. Recent studies have emphasized the use of alternative imaging modalities to detect and diagnose breast carcinoma, including ultrasonography (US), magnetic resonance imaging, and nuclear medicine studies. However, the radiologist can take a number of steps that will significantly enhance the accuracy of image interpretation at mammography and decrease the false-negative rate. These steps include performing diagnostic as well as screening mammography, reviewing clinical data and using US to help assess a palpable or mammographically detected mass, strictly adhering to positioning and technical requirements, being alert to subtle features of breast cancers, comparing recent images with earlier mammograms to look for subtle increases in lesion size, looking for additional lesions when one abnormality is seen, and judging a lesion by its most malignant features.

Fibroepithelial lesions of the breast are commonly seen in clinical practice. The masses are composed of a combination of prominent stroma and varying glandular elements. Fibroadenomas, benign lesions that derive from the terminal duct lobular unit, are the most common and are often identified at clinical examination or mammography as circumscribed masses. Benign mesenchymal tumors include focal fibrosis, pseudoangiomatous stromal hyperplasia, and fibromatosis or desmoid tumor. Phyllodes tumor, which is similar to fibroadenoma but has increased cellularity in the stroma, is typically benign but has malignant potential. Diabetic fibrous mastopathy, a stromal proliferation found in patients with juvenile-onset insulin-dependent diabetes, is a reactive fibrous lesion. Most of these lesions manifest as masses at clinical and/or mammographic examination. Some (eg, fibroadenomas) may be associated with calcifications. Except for fibromatosis and phyllodes tumor, fibroepithelial lesions need not be excised if the diagnosis is confirmed by the results of histologic analysis at percutaneous biopsy. To correctly differentiate between fibrous breast lesions that are benign and those that should be resected, the physician must be familiar with the correlated radiologic-pathologic findings in the various lesion types.

The American College of Radiology (ACR) Breast Imaging Reporting and Data System (BI-RADS) defines four different types of asymmetric breast findings: asymmetric breast tissue, densities seen in one projection, architectural distortion, and focal asymmetric densities. These lesions are frequently encountered at screening and diagnostic mammography and are significant because they may indicate a neoplasm, especially if an associated palpable mass is present. Once these lesions are detected at standard mammography, supplementary breast imaging with additional mammographic views and ultrasonography (US) can be a key aspect of work-up. The role of US in this setting has not been clearly defined. However, a positive US finding such as a solid mass or an area of focal shadowing increases the level of suspicion for malignancy. A thorough knowledge of the patient's clinical history, along with a fundamental understanding of the ACR BI-RADS lexicon and the role and limitations of supplementary breast imaging, will allow more accurate interpretation of these potentially perplexing soft-tissue findings.

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Detection and management of breast abnormalities that develop during pregnancy and lactation is difficult for both the clinician and the radiologist. This article reviews the hormonal and physiologic effects on the breast during pregnancy and lactation. Breast masses that occur in pregnant or lactating patients, including pregnancy-associated breast cancer, are discussed and the corresponding ultrasound and mammographic findings are presented. Finally, a rationale for the imaging evaluation and management of the pregnant or lactating patient with a breast mass are presented.