ULTRASOUND OF THE BREAST

Bruno D. Fornage, MD

The University of Texas MO Anderson Cancer Center, Houston, Texas

The evaluation of breast diseases is based on physical examination and mammography. Sonography is the best adjunct to mammography at the present time.

Technical considerations The superiority of hand-held transducers over water-path systems lies in their higher frequency and real-time capability. Because of their near field is wider and provides a better resolution, linear-array transducers are more effective than sector probes. 7.5-MHz probes are routinely used while a 5-MHz probe may be required to evaluate large breasts. The use of a stand-off pad allows examination of the skin and superficial tissues. Both breasts and axillae are examined.

Normal ultrasound anatomy The skin appears as a thin layer of moderately echogenic tissue about 1 to 3 mm in thickness. The areola and the nipple are slightly hypoechoic. Cooper's ligament appears as echogenic'spicules indenting the hypoechoic subcutaneous fatty layer. The echogenicity of breast tissue varies according to the relative proportions of connective, epithelial, and fatty components. With high frequency transducers, lactiferous ducts can be identified. A deep fatty layer is seen anterior to the thoracic wall

Benign pathologic conditions

Fibrocvstic disease Fibrocystic disease comprises cysts, stromal (fibrous) hyperplasia. and proliferative fibrocystic disease which includes ductal epithelial hyperplasia, papillomatosis, lobular hyperplasia, and sclerosing adenosis. There is no specific sonographic pattern for proliferative fibrocystic disease. Cysts Typical cysts are sonolucent, well-circumscribed, and associated with distal sound beam enhancement. However, 20 to 30% of cysts do not fulfill all of the classic sonographic criteria, and some of them mimic a solid hypoechoic mass. A thickened wall is often seen in chronic or infected cysts. Inspissated cysts may either show some intemal echoes or present as anechoic structures. Sonography can display calcified deposits in the wall of chronic cysts.

Fibroadenomas Typically, fibroadenomas present as hypoechoic, homogeneous masses with smooth (tabulated) margins. Rarely, fibroadenomas without calcifications cast a marked shadow. Internal calcifications are found in about 10% of fibroadenomas. Fibroadenomas are elongated with their greatest diameter parallel to the skin. Occasionally, small fibroadenomas surrounded by fat cannot be identified.

Cystosarcoma Dhyllodes Cystosarcoma phyllodes, which may be either benign or malignant, is a rare variant of f ibroadenoma with a highly cellular, sarcoma-like stroma. It often presents as a fibroadenoma. Fluid-filled clefts and areas of necrosis can be seen.

Abscesses Breast abscesses are rare except during lactation. They are frequently located in the retroareolar area. They usually appear as hypoechoic masses with occasional echogenic debris and gas bubbles. Margins are blurred and irregular. pat necrosis Fat necrosis usually develops after trauma. Architectural distortion -3 Y

and calcifications render the lesion suspicious for malignancy on mammography. Sonography shows an id-defined hypoechoic area and biopsy is usually required to rule out malignancy. Oily cysts may appear as sonolucent areas.

Quctal pathology Ductal ectasia is readily demonstrated with the use of high-resolution transducers. Intraductal papillomas are small tumors which are best demonstrated on galactography. Large papiltomas may appear on sonograms as nonspecific hypoechoic rounded masses. Because of their marked cellularity, papillomas may be at the origin of falsely suspicious results on fine-needle aspiration.

Gynecomastia Sonographic patterns of gynecomastia have not been extensively evaluated. Sonography can differentiate focal from diffuse changes.

Carcinomas With the use of state-of-the-art, hand-held equipment, masses as small as 1 cm in diameter are reliably identified on sonography. Whatever its histologic type, breast carcinoma usually appears as a focal hypoechoic mass, disrupting the smooth architecture of breast tissue planes. The margins are irregular and echotexture is nonhomogeneous. Acoustic shadowing is found in less than 50% of cases. Invasive carcinomas are associated with a d'jsmoplastic reaction made of fibrosis and edema, which appears as an ill-defined echogenic rim surrounding the hypoechoic malignant core. Clustered microcateifications can be depicted within hypoechoic tumors with the use of 7.5-MHz transducers. Unlike fibroadenomas, carcinomas are spheric or tend to grow antoroposteriorly with a length/ anteroposterior diameter ratio less than 1. About 10-15% of carcinomas present at, well-circumscribed nodules on both mammograms and sonograms. Of this group, medullary carcinomas are markedly hypoechoic with occasional distal acoustic enhancement. On occasions, sonography can demonstrate carcinomas not seen on mammograms particularly in dense breasts, breasts with postsurgical or postirradiation changes, or breasts with prosthetat. Sonography can also deted the rare intracystic carcinomas. i/

Doppíer analysis • Abnormal Doppler signals are detected mainly at the periphery of malignant tumors.

Tumor size measurement Sonography has proved accurate in the measurement of the size of breast carcinomas. Follow-up measurements are essential in the evaluation of response to therapy.

lymph nodes Sonography can visualize enlarged metastatic lymph nodes in the axilla, the infra- and supraclavicular areas, and along the internal mammary chains. They appear as hypoechoic rounded masses.

Post-treatment patterns Postirradiation changes include skin thickening and an overall disorganization of breast architecture. In those patients, sonography still has the capability of detecting early recurrence. After surgery, deep scars may appear as stellate ochogenic patterns. A hematoma is commonly found in the weeks following surgical biopsy. Lymphoceles are not rare after an axillary lymph node dissection.

Recurrences Mammography may be of limited value because of post-surgical or post-irradiation changes. A hypoechoic mass developing in a conservatively treated breast is suspicious for local recurrence and requires an US-guided fine-needle aspiration.

Complementary roles of sonography and mammography Sonography and mammography are two different and complementary imaging techniques for the breast. Mammography is the gold standard for the detection of isolated microcalcifications and millimetric carcinomas. However, sonography with state-of-the-art equipment can visualize masses as small at 1 cm in diameter in almost every type of breast. The unique cross-sectional and real-time imaging capabilities of sonography make it the technique of choice for guidance of fine-needle aspiration biopsy of nonpalpable breast masses while its role in pre- or intraoperative localization of such tumors is expanding. Major limitations of sonography include its operator dependence, the absence of global imaging of the breast, problems in reprodudbiKty, and its inability to delineate carcinomas less than 0.7-0.8 cm. It has to be determined whether breast sonography should be restricted to the evaluation of indeterminate densities on mammography or used more widely in symptomatic patients. For example, both mammography and sonography are performed systematical/ in symptomatic patients in Europe. Ultrasound guided fine-needle aspiration of nonpalpable lesions now provides an effective alternative to follow-up mammograms in the case of indeterminate densities. It is important to reemphasize that state-of-the-art equipment and rigorous technique must be used while the limitations of the method should be kept in mind.

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