Evaluation of Abnormal Screening Mammograms

Transcription

1 342 Evaluation of Abnormal Screening Mammograms Ellen Shaw de Paredes, M.D. The purpose of routine screening mammography is to detect unsuspected cancer that has the potential to be cured. Abnormalities detected on the screening examination often necessitate additional radiologic workup before a definitive result or diagnosis can be given. This workup (diagnostic mammography) may include specialized views, such as spot compression to evaluate the margins of a nodule, or magnification views to determine the features of microcalcifications. Additional evaluation with mammographic views, breast ultrasound, and, at times, interventional procedures such as fine needle aspiration or core biopsy are performed to complete the radiologic evaluation of a patient with an abnormal mammogram. Signs of malignancy include nodules (most often poorly defined), microcalcifications, and, less commonly, areas of architectural distortion, asymmetry, or focal ductal dilatation. A comprehensive approach to breast imaging will help to potentiate the early detection of subtle malignancies and avoid the performance of some biopsies for benign lesions. Cancer 1994; 74: Key words: mammogram, screening, breast, cancer, diagnostic, evaluation, intervention. Numerous randomized trials'-3 have shown the benefits of screening mammography in the early detection of breast cancer. Results of the trial conducted by the Health Insurance Plan of New York,' in which women were randomized into screening and control groups, demonstrated an overall reduction in mortality from breast cancer of 40% at 9 years in those women older than 50 years who were screened. The Breast Cancer Detection Demonstration Project,' in which all women who participated were screened with mammography Presented at the National Conference on Breast Cancer, Boston, Massachusetts, August 26-28, From the Department of Radiology, University of Virginia, Charlottesville, Virginia. 1 thank Barbara Lechner for her kind assistance in the preparation of the manuscript. Address for reprints: Ellen Shaw de Paredes, M.D., University of Virginia, Health Sciences Center, Diagnostic Center for Women, Box 493, Charlottesville, VA Accepted for publication January 31, and breast physical examination, demonstrated the important role of screening mammography in the early detection of breast cancer. Of all cancers found in the Breast Cancer Detection Demonstration Project, 42% were detected by mammography alone. In Sweden, the two-county or W-E trial, a randomized controlled trial evaluating the efficacy of mammography alone in the detection of breast cancer, also demonstrated an overall mortality reduction of 31Y0.~ Based on these and other studies, mammography guidelines for the routine screening of asymptomatic women have been establi~hed.~,~ Debate continues on the age at which to begin and the appropriate frequency of screening, yet there is general consensus among many organizations that periodic screening with mammography and physical examination should be a part of a woman's regular health care. Screening Mammography The purpose of screening mammography is to detect unsuspected cancer in asymptomatic women. Screening mammography is normally a two-view examination of each breast, including mediolateral oblique and craniocaudal views6 Careful attention by the mammography technologist to quality assurance, and proper positioning and compression of the breast are necessary for the obtaining of optimum images and for a maximum benefit from screening to occur. Screening may be performed with or without onsite direct supervision of the radiologist. In interpreting the screening mammogram, the radiologist must determine if any abnormalities are present. Sometimes a definitive diagnosis and/or recommendation for management can be made on the basis of the screening study; however, further imaging procedures often are performed to evaluate and determine the significance of abnormalities that are identified. It is also extremely helpful and important for the radiologist to compare the current screening study with prior mammograms to assess the level of significance of the abnormality detected as well as any interval change.

2 Evaluation of Abnormal Screening MammogramslShaw de Paredes 343 Figure 1. A well defined mass (arrow) is present on the craniocaudal view (left) but is not seen on the mediolateral oblique view (center). An additional lateromedial view (right) demonstrates that the lesion is located in the upper, inner quadrant (arrow). Diagnostic Mammography Diagnostic or problem-solving mammography is a more comprehensive radiologic evaluation of a breast abnormality. A diagnostic mammogram often includes both routine mediolateral oblique and craniocaudal views as well as additional mammographic views to evaluate specifically the abnormality noted on the screening study or during the physical examination (Fig. 1). Additional imaging procedures, such as breast ultrasound or interventional procedures, may be performed as adjuncts to the diagnostic mammogram to complete the evaluation of the abnormality noted. A diagnostic mammogram may be performed for several reasons, including the following: to evaluate an abnormality detected on a screening mammogram, to evaluate a patient with an abnormal clinical examination that includes such findings as a palpable lump or spontaneous nipple discharge, and to evaluate a patient with a complex surgical history, such as on who has had breast implants or treatment of breast cancer with breast conservation therapy, in which case additional views might be performed routinely. Clinical findings are correlated with mammographic findings to be certain that they represent the same lesion. The technologist should indicate the palpable findings with a radiopaque marker so that its location will be demonstrated on the mammographic images, and a more accurate method of correlation of mammographic and clinical findings can be performed. Particularly in the cases of palpable masses that are not evident on mammography or for palpable or nonpalpable masses that are well circumscribed on mammography, breast ultrasound can provide valuable adjunctive information about the internal characteristics of the lesion (Fig. 2). Additional mammographic views are performed for two basic reasons, namely, to determine the location of an abnormality if seen on only one of the routine screening views and to determine the morphologic characteristics and significance of the lesion.* Determination of the location of the lesion is especially important for a nonpalpable lesion in which radiologic guidance would be necessary for biopsy. Among the types of views that are performed to determine the location of

3 344 CANCER Supplement July 2, 2994, Volume 74, No. 1 Figure 2. A well defined medium density nodule (arrow) noted on mammography (left) is found to be a simple cyst on ultrasound (right) a lesion are the 90 mediolateral view or exaggerated medial or lateral craniocaudal views. Numerous other views are available for the radiologist and technologist to employ to see the lesion, particularly when it is located posteriorly or when it is superimposed over dense glandular tissue. A knowledge of the advantages and utility of each view is important so that the proper additional views can be selected and performed to provide the needed information without unnecessary radiation exposures. Specialized views to evaluate morphologic features of lesions often are used to determine the level of suspicion of the lesion detected and the need for biopsy. Spot compression often is used to evaluate a seemingly well defined nodule so that its margination can be defined more ~learly.~ The determination of the margination is very important to the decision as to whether a biopsy should be performed on a nodule. Spot compression of a nodule is very helpful to determine a nodule's density, shape, and margination, features used to differentiate those lesions that are likely benign from those that are likely malignant." In addition, spot compression can be helpful in demonstrating the fatty hilum of a nodule thought to be an intramammary lymph node (Fig. 3). During spot compression, the technologist determines the area of the breast in which the lesion is located by viewing the mammogram in conjunction with visual inspection of the breast. During spot compression, only a small area of the breast is compressed maximally, allowing for displacement of overlying fibroglandular tissue and better imaging of a focal lesion. This will allow for confirmation of the presence of a nodule and an evaluation of its features. Magnification mammography is used to evaluate fine detail areas such as microcalcifications. With a magnification view, one is better able to see microcalcifications and, in particular, determine their morphology, a key factor in assessment to determine the need for a biopsy. To perform the magnification view, a microfocal spot is used and the breast is placed on a platform above the film and cassette to create the magnification factor."

4 Evaluation of Abnormal Screening Mammograms/Shaw de Paredes 345 Figure 3. A small nodule (arrow) located posteriorly in the mediolateral oblique view (left) is seen to be very well defined and to contain a fatty hilum (arrow) on the spot view (right), consistent with the finding of an intramammary lymph node. Approach to Breast Abnormalities Masses The types of abnormalities that can be found on mammography include the following: masses, calcifications, areas of asymmetry and architectural distortion, dilated lactiferous ducts, and skin or nipple thickening or retraction. The additional views described above, as well as other positioning, and ultrasound are used to evaluate such findings and to determine a recommendation for management of the patient. The correlation of the patient's history and clinical findings is important to mammographic interpretation. It is helpful for the technologist to mark any palpable lumps, skin lesions and scars with radiopaque markers, so that these areas can be correlated directly with any mammographic findings. The evaluation of a mass lesion is based on an assessment of its shape, borders, density, size, orientation, presence of a fatty halo, and any associated findings. Masses that are round or oval and have very well defined margins are more likely to be of a benign nature in contrast to those that are spiculated or poorly defined, which are more likely to be malignant. The density of a

5 346 CANCER Supplement July 7, 2994, Volume 74, No. 1 well defined mass is important to its management. Well defined masses that are radiolucent or of heterogeneous density (i.e., fat containing masses) are virtually all benign and need no further imaging or surgical evaluation. Fat-containing masses include lipomas, galactoceles, oil cysts, hamartomas, intramammary lymph nodes, and focal fibroglandular tissue. Medium- or high-density well defined masses can be manifestations of lesions such as cysts, fibroadenomas, hematomas, abscesses, cystosarcoma phylloides, lymph nodes, metastases, and carcinomas. When a well defined mass of medium or high density is identified on an initial mammogram or has grown or developed since earlier studies, ultrasound is performed to determine if the mass is cystic or solid. Solid masses, particularly those that are more than 1 cm in greatest dimension or those that have grown or developed since prior mammograms, usually are evaluated by a biopsy procedure. Masses that are found to be cystic on ultrasound can be followed routinely unless they are symptomatic or contain atypical findings on ultrasound (e.g., internal echoes or wall irregularity), in which cases they may be aspirated. 7,12 The fatty halo that may surround a well circumscribed mass is a strong indicator of benignancy if it completely surrounds the mass; however, it is not diagnostic of a benign lesion. Swann et al.13 found that 25 of 1000 breast cancers had a positive halo sign. The types of breast cancer that have a tendency to present as relatively well defined masses include medullary, mucinous, and intracystic carcinomas. Because nonspecified infiltrating ductal carcinoma accounts for the majority of all breast cancers, however, the most likely histology of a well circumscribed carcinoma is infiltrating ductal carcinoma. In addition, small nonpalpable cancers may have relatively benign features,14 such as relatively well defined or partially ill-defined margins. Spot compression is helpful to demonstrate indistinctness of the margins of a small nodule that would warrant biopsy. An ill-defined or spiculated mass on mammography has a higher probability of being positively predictive of a malignancy. The classic appearance of breast cancer is as a high density mass with fine tendrils or spicules surrounding its margin^'^,'^; this is particularly the case of infiltrating ductal carcinoma (Fig. 4). Because of the different pattern of growth in infiltrating lobular carcinomas-a linear arrangement of tumor cells through the normal tissue-these tumors may present mammographically as areas of asymmetric density or architectural distortion without a central high-density tumor rnass.i7 Such cancers may distort the normal parenchymal architecture surrounding them, creating the appearance of a pulling or tethering of the tissue. Benign lesions that may mimic carcinoma because of their tendency to present as spiculated masses include posttraumatic changes and radial scars. The history of surgery or significant blunt trauma to the site of the mammographic abnormality should suggest the possibility that it represents postoperative or posttraumatic hematoma or scar. Scars have a tendency to have a different shape and density on orthogonal views, whereas cancers tend to maintain the same appearance. Radial scars are usually nonpalpable areas of focal architectural distortion without a high-density center. Pathologically, these are nontraumatic proliferative lesions composed of a fibroelastic core that is surrounded by lobules radiating outward in a spoke-wheel orientation. Calcifications The analysis of breast calcifications is based on the following features: morphology, size, distribution, orientation, variability, and stability. Morphology and distribution are extremely important in the determination of the probable etiology of calcifications and their management. Many benign conditions in the breast, including such processes as fibroadenomas, fat necrosis, cystic hyperplasia, atherosclerosis, dermal lesions, and plasma cell mastitis, can present with calcifications but are pathognomonically benign and do not require either early follow-up or an interventional procedure. The calcifications of fibroadenornas2 are usually coarse macrocalcifications with smooth margins and are located within a soft tissue nodule. Fat necrosis and dermal calcifications have smooth, round, ring-like shapes. The calcifications of secretory disease, which is associated with plasma cell mastitis, are smooth, linear, needle-like macrocalcifications that lie in the main lactiferous duct and are oriented toward the nipple. Arterial calcifications are seen readily on mammography as circuitous tram-line deposits within the walls of vessels. The analysis of microcalcifications is more complex because these deposits may be associated with breast carcinomas. Generally, microcalcifications can be divided into two groups based on their morphology. Lobular microcalcifications are located in the most terminal part of the glandular system, the ductule, and because they are located in these small, blind-ending pouches, they have smooth margins and round shapes. Lobular calcifications tend to be of similar size and shape and to be either loosely grouped or diffuse. The etiology of lobular microcalcifications include various forms of fibrocystic change, including adenosis, sclerosing adenosis, and lobular hyperplasia; these calcifications also can be associated with lobular carcinoma in sit^.^^ Ductal microcalcifications are the second morphologic group of breast microcalcifications. Ductal calcifi-

6 Evaluation of Abnormal Screening Mammograms/Shaw dr Paredes 347 Figure 4. Left craniocaudal view (left) demonstrates a rounded medium density, 1-cm nodule laterally (arrow). On spot compression, this is shown to have irregular, spiculated margins, consistent with the finding of carcinoma. cations are located primarily in the extralobular terminal duct, the small terminal branches of the lactiferous duct system. These calcifications may be formed by the active secretion of calcium salts by epithelial cells into the duct lumen24 or by the calcification of necrotic debris in cases of comedocarcinoma. When ductal microcalcifications are present, one usually must perform a biopsy to exclude the possibility of carcinoma, because of the relatively high likelihood of their indicating malignancy. Etiology of ductal calcifications include benign conditions, such as epithelial hyperplasia and atypical ductal hyperplasia, as well as various forms of ductal carcinoma. The morphology of these deposits is often irregular, jagged, linear, or branching,25 and there is variability in their size and shape (Fig. 5). Malignant microcalcifications tend to be distributed in tight clusters or in a segmental orientation but may involve an entire breast in cases of extensive ductal carcinoma. Magnification mammography is quite helpful in the assessment of morphology and distribution of microcalcifications to determine their probable etiology. associated with a mass lesion. Areas of asymmetry are an infrequent manifestation of breast cancer but may be regarded with concern if they are new and focal, palpable, or associated with other findings such as microcalcifications or architectural distortion. Dilated lactiferous Other Signs of Malignancy Other signs of malignancy include areas of focal asymmetry with or without distortion of architecture and dilated lactiferous ducts. Focal or diffuse skin thickening or retraction may be a manifestation of malignant breast disease, but this finding often is evident clinically and is Figure 5. Localization wire marks a cluster of pleiomorphic microcalcifications with irregular margins (pathology: intraductal carcinoma). Adjacent are round macrocalcifications typical of fat necrosis.

7 348 CANCER Supplement July I, 1994, Volume 74, No. 1 findings be correlated. For lesions that mammographically are highly suspicious, and in which the needle biopsy is benign, excisional biopsy is indicated for confirmation. As we gain more knowledge about the specific types of lesions that benefit most from needle biopsy and about the effectiveness and limitations of these procedures, we may be able to make a significant impact on decreasing the number of benign excisional breast biopsies. References Figure 6. Stereotactic guidance allows for highly accurate needle placement into small nonpalpable lesions for a fine needle aspiration biopsy. ducts most often represent benign conditions, such as duct ectasia or intraductal papillomas. The presence of a solitary dilated duct or multiple markedly asymmetric dilated ducts suggests a focal intraductal process, and a biopsy often is performed in these cases." lnterventional Procedures When both clinical and mammographic findings concur, either a fine needle aspiration or surgical biopsy can be performed on a mass based on palpation (Fig. 6). For nonpalpable, mammographically identified suspicious lesions, imaging guidance is needed for biopsy. Until recently in the United States, the vast majority of nonpalpable mammographic lesions were localized by the placement of a needle, dye, or a hook wire in the region of the abnormality under mammographic guidance. Once the area was localized and removed surgically, the tissue was radiographed to confirm that the lesion seen on mammography was included. The advent of stereotaxis in mammography has allowed for very accurate needle placement into small, nonpalpable lesions. Techniques of fine needle aspiration biopsy and core biopsy under stereotactic guidance now are used to diagnose many types of nonpalpable breast lesions. For fine needle aspiration biopsy, a thin needle (often 22 gauge) is used to sample cells for cytologic analysis. Core biopsy involves removing a core of tissue with a biopsy gun that contains needles ranging from 14 to 18 gauge. These sampling techniques require very accurate needle placement, skillful performance of the sampling procedure by the radiologist, and expert pathologic examination to interpret the specimens, particularly for cytologic It is extremely important that mammographic and cytologic or pathologic 1. Strax P, Veret L, Shapiro S. Value of mammography in reduction of mortality from breast cancer in mass screening. AIR Am / Roentgenol 1973; 67: Baker LH. Breast cancer detection demonstration project: fiveyear summary report. CA Cancer] Clin 1982; 32: Tabar L, Fagerberg CJG, Gad A, Baldetorp L, Holmberg LH, Grontoft 0, et al. Reduction in mortality from breast cancer after mass screening with mammography: randomized trial from the Breast Cancer Screening Working Group of the Swedish National Board of Health and Welfare. Lancet 1985; 1: Smith R. Breast cancer screening guidelines. Womens Health Issues 1992; 2: American Cancer Society. Mammography: two statements of the American Cancer Society. New York: American Cancer Society Professional Education Publication, American College of Radiology. Standards for the performance of screening mammography: mammography accreditatio? program. American College of Radiology, Jackson VP. The role of US in breast imaging. Radiology 1990; 177: Sickles EA. Practical solutions to common mammographic problems: tailoring the examination. AIR Am I Roentgenol 1988; 151: Berkowitz JE, Gatewood OMB, Gayler BW. Equivocal mammographic findings: evaluation with spot compression. Radiology 1989; 171: Shaw de Paredes E. Atlas of film-screen mammography. Baltimore: Williams & Wilkins, Sickles EA. Microfocal spot magnification mammography using xeroradiographic and screen-film recording systems. Radiology 1979; 131: Sickles EA, Filly RA, Callen PW. Benign breast lesions: ultra- 'sound detection and diagnosis. Radiology 1984; 151: Swann CA, Kopans DB, Koerner FC, McCarthy KA, White G, Hall DA, et al. The halo sign of malignant breast lesions. AIR Am ] Roentgenol 1987; 149: Sickles E. Mammographic features of 300 consecutive nonpalpable breast cancers. AIR Am ] Roentgenol 1986; 146: Leborgne R. Diagnosis of tumors of the breast by simple roentgenography: calcifications in carcinoma. AIR Am I Roentgenol 1951; 65: Lundgren B. Malignant features of breast tumours at radiography. Acta Radiol 1978; 19: Mendelson EB, Harris KM, Doshi N, Tobon H. Infiltrating lobular carcinoma: mammographic patterns with pathologic correlation. AIR Am I Roentgenol 1989; 153: Bassett LW, Gold RH, Cove HC. Mammographic spectrum of traumatic fat necrosis: the fallibility of "pathognomonic" signs of carcinoma. AJRAm IRoentgenol 1978; 130:

8 Evaluation of Abnormal Screening MammogramslShaw de Paredes Andersen JA, Gram JB. Radial scar in the female breast: a longterm follow up study of 32 cases. Cancer 1984; 53: Gershon-Cohen J, lngleby H. Roentgenography of fibroadenomas of the breast. Radiology 1952; 59: Leborgne R. Esteatonecrosis quistica calcificata de la mamma. Torace 1967; 16: Kopans DB, Meyer JE, Homer MJ, Grabbe J. Dermal deposits mistaken for breast calcifications. Radiology 1983; 149: Pope TL Jr, Fechner RE, Wilhelm MC, Wanebo HI, deparedes ES, et al. Lobular carcinoma in situ of the breast: mammographic features. Radiology 1988; 168:63-6. Ahmed A. Calcification in human breast carcinoma: ultrastructural observations. Pathol 1975; Tabar L, Dean PB. Teaching atlas of mammography. Stuttgart: Thieme Verlag, Shaw de Paredes E. Radiographic breast anatomy: radiological signs of breast cancer. In: Technical aspects of breast imaging: clinical aspects of breast cancer and mammography. Radiological Society of North America course syllabus, 1992.