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Breast Imaging: the Role of Alternative Diagnostic Modalities

Posted on: Saturday, 9 April 2005, 03:00 CDT

Breast cancer continues to be the highest incident cancer and the second leading cause of cancer-related death in US women. This year approximately 275,000 women will be diagnosed with the disease and 40,110 will succumb.1 American women have a one in seven risk of developing the disease and factors such as personal history of breast or ovarian cancer, atypia, lobular carcinoma insitu or genetic aberrations such as BRCAl or BRCA2 increase the risk for developing breast cancer. While patients with BRCA mutations comprise only about 5 to 10% of women with breast cancer, their risk for developing breast cancer is 50 to 85% .2 The gold standard for breast cancer detection is mammography. Screening mammography, in randomized controlled studies, has been shown to decrease breast cancer mortality by 24%.3 For each 1000 women who are screened, breast cancer is detected in 5 to 7 at first screen and two to three on subsequent regular annual screenings.

However, mammography does not identify all breast cancers. It had serious limitations in discovering tumors in women with dense mammary parenchyma and further lacks the ability to characterize lesions at screening. While many lesions can be characterized with a diagnostic mammogram, some abnormalities rely on the use of other imaging modalities and imaging-guided interventions. It is the goal of this paper to discuss the role of these alternatives.

A common misconception is that digital mammography is a different examination from film screen mammography. The digital mammogram merely employs a different image receptor; the image is acquired electronically rather than with film-screen. Although the image obtained can be viewed as film, in most practices it rarely is, but is viewed on a high-resolution computer monitor. These images can be stored electronically, eliminating the need for film, and images can be sent electronically for remote viewing. For the patient, the procedure is faster because the images are evaluated in real time and there is no wait for film processing. Most patients perceive the examination to be more comfortable. The quality of the images obtained is equal to filmscreen mammography. Digital mammography is superior in assessing the dense breast because the image can be windowed and leveled for improved tissue contrast. The radiation dose is about the same, although slightly less for the patient with dense breasts.

Breast ultrasound has advanced beyond the differentiation of solid versus cystic masses with the advent of the higher frequency transducers in the early 1990s. To perform breast ultrasound, a transducer with a frequency in excess of 7.5 mHz is necessary. At this time, breast ultrasound is neither a routine screening tool nor does it replace mammography as the first line of evaluation for palpable masses except in the peripubertal patient, the patient with dense breasts with a palpable mass or in patients with metastatic disease and a negative mammogram. There are ongoing studies both in Israel and by ACRIN (American College of Radiology Imaging Network) evaluating ultrasound as a screening tool. To date, the variability of both equipment and operators, and the labor intensity required are substantial deterrents for using ultrasound as screening.

Ultrasound now plays a routine role in assessing palpable breast masses, characterizing mammographically detected masses, evaluating focal breast pain, evaluating tumor size, assessing response to neoadjuvant chemotherapy, staging the axilla of cancer patients, and for guiding interventions such as cyst aspirations or biopsies. The ability of ultrasound to characterize masses was first noted in the early 1990s when Fornage began evaluating fibroadenomas and found that the length to anteroposterior dimension of the fibroadenoma was greater than 1.4 in 86 percent and less than 1.4 in 100% of malignant tumors. 4 This was followed by a seminal article by Stavrok in 1995 that evaluated 750 solid masses and extrapolated from these cases criteria to distinguish malignant from benign masses.5 While there are limitations, theses studies were the beginning of the widespread use of ultrasound to characterize solid breast masses.

Imaging-guided biopsies have transformed the diagnosis and management of benign and malignant breast masses. With the advent of the computerized stereotactic equipment, stereotactic breast biopsies were first introduced in Sweden in 1976 and in the United States in the late 1980s.6 Stereotactic needle-guided biopsies have been performed in Rhode Island since 1991. The stereotactic breast biopsy is a mammographically (x-ray) guided procedure that pinpoints breast lesions to within 1-2 mm. The procedure may be performed with a special table where the patient lies prone or with conventional mammographic equipment with the patient upright. Each has advantages. With the prone table there is less patient motion and less syncope, and the patient does not view the biopsy being performed. However, the add-on device for the standard mammographic unit is far less expensive and suits the low volume situation more ideally. Mammographic guidance (stereotactic biopsies) are reserved for those lesions that cannot be seen with ultrasound.

Ultrasound guided biopsies require the use of ultrasound equipment with high frequency transducers. Any lesion mat can be seen with ultrasound should use ultrasound guidance to guide the biopsy to ensure that the actual lesion itself is first characterized. If the mass is a cyst, no further intervention is required unless the cyst is painful or its sonographic appearance is complex. Ultrasound guidance ensures complete aspiration of cysts. If a cyst does not aspirate completely, biopsy should be performed. Ultrasound ensures accurate sampling of both palpable and nonpalpable solid masses. Even palpable lesions are more accurately sampled with ultrasound guidance.

A variety of needle systems are available to perform both stereotactic and ultrasound-guided biopsies. These range from needles of tiny caliber (FNA) to larger needles (9-14g) spring- loaded or vacuum assistance for so-called large core needle biopsies. The use of FNA is limited both because of the paucity of qualified cytopathologists and the inability to determine whether an identified tumor is invasive. The accuracy of image-guided biopsies is reported in several series to be greater than 98%.

The latest tool in the breast imaging armamentarium is magnetic resonance imaging (MRI). First used in 1986, its value was impaired due to insufficient standardization of the technique, lack of reproducibility and the need for intravenous contrast injection. Further requirements include an MRI unit with field strength of 1.5 Tesla or greater and a dedicated breast coils. To perform the procedure for the detection of breast cancer the equipment must also be equipped to employ high spatial and temporal resolution and create thin slices. Since the examination is restricted to the "closed" magnet, patients with claustrophobia are excluded. The exam takes about 25 minutes. Furthermore, breast MRI is highly sensitive but not highly specific, with reports of sensitivity for invasive breast cancer approaching 100%. For DCIS, reports of sensitivity range from 50 to 90%. For DCIS, MRI and mammography are complementary with mammography detecting five to 10% of the cases that are not detected with MRI because of the presence of microcalcifications.7

Both sensitivity and specificity depend on patient selection, MR technique, level of experience, interpretation guidelines an intimate understanding of mammographic images for correlative purposes. A variety of issues can affect MRI interpretation. MRI characteristics of benign and malignant lesions can overlap. Hormonal status of the patient can affect the image and ideally, for the menstruating patient, the exam should be performed on days six through 18 of the menstrual cycle. Hormone replacement therapy can affect the images as well. Limitations of the study include a significant false positive rate, with one false positive per 5 to 10 studies. Other limitations include the need to be able to biopsy with MRI guidance since a certain number of lesions are not detected by other imaging modalities or by physical examinarion. Clearly, the interpretation is dependent upon the expertise of the radiologist in reading breast MR, breast ultrasound and mammography.

There are now numerous indications for breast MRI. It is indicated preoperatively for staging newly diagnosed breast cancer because the findings may alter the extent or type of surgery planned. It is also valuable in assessing response to neo-adjuvant chemotherapy. In patients with a history of breast cancer, it is useful in assessing post-operative residual tumor as well as for disease recurrence. Other indications include evaluating for occult tumor in patients with metastatic disease in the axilla whose mammogram, ultrasound and physical examination are negative. Breast MRI should also be used to screening high risk women, particularly those with genetic mutations such as BRCAl and BRCA2, in women who have a first degree relative with premenopausal breast cancer, and in those women who have a personal history of breast or ovarian cancer particularly if their mammogram demonstrates dense breast tissue. In an article by Kriege et al, MRI was shown to be more sensitive than ma\mmography in detecting tumor in women with an inherited susceptibility to breast cancer.8 At the current time breast MRI is not indicated for routine screening, not only because of expense, but also because there is a high incidence of false positivity necessitating an increased number of biopsies. Other contraindications include the presence of pacemakers, aneurysm clips, or claustrophobia. MRI does not replace mammography as a screening tool for the general population.

In summary, mammography remains the gold standard for breast cancer screening. While ultrasound and image-guided interventions have become standard ancillary procedures in breast cancer diagnosis, MRI now begins to play an increasingly important, but limited, role in assessing for breast cancer in selected groups.

ACKNOWLEDGEMENT

The author wishes to thank Martha Maineiero, MD, for her editorial assistance.

THE LATEST TOOL IN THE BREAST IMAGING ARMAMENTARIUM IS MRI.

REFERENCES

1. Jemal A, Tiwari RC, Murray T, et al. Cancer statistics, 2004. CA Cancer J Clin 2004;54:8-29.

2. Burke W, Daly M, Garber J, et al. Recommendations for follow- up care of individuals with an inherited predisposition to cancer. II. BRAC1 and BRCA2. JAMA 1997; 277:997-1003.

3. Smith RA, Saslow D, Sawyer KA, et al. American Cancer Society guidelines for breast cancer screening update 2003. CA Cancer J Clin 2003;53:141-9.

4. Fornage BD, Sneige N, Faroux MH, Andry E. Sonographic appearance and ultrasound-guided ine-needl aspiration biopsy of breast carcinomas smaller than 1 cm3. J Ultra Med 1990; 9:559-68.

5. Stavros AT, Thickman D, Rapp CL, et al. Solid breast nodules: use of sonography to distinguish between benign and malignant lesions. Radiol 1995; 196:123-34.

6. Bulmgren J, Jacobson B, Nordenstrom B. Stereotaxix instrument for needle biopsy of the mamma. Am J Roentgenol 1977; 129:121-5.

7. Lee SG, Orel SG, Woo IJ, et al. MR imaging of the contracterai breast in patients with newly diagnosed breast cancer, preliminary results. Radiol 2003; 226:773-8.

8. Kriege M, Brekelmans C, Boetes C, et al Efficicacy of MRI and mammography for breast-cancer screening in women with a familial or genetic predisposition. NEJM 2004; 351:427-37.

BARBARA SCHEPPS, MD

Barbara Schepps, MD, is Director, Anne C. Pappus Center for Breast Imaging, Rhode Island Hospital, and Professor of Diagnostic Imaging (Clincal), Brown Medical School.

CORRESPONDENCE:

Barbara Schepps, MD

Department of Diagnostic Imaging

Rhode Island Hospital

593 Eddy Street

Providence, RI 02903

Phone: (401) 444-5184

Fax: (401) 444-5017

E-mail: bschepps@lifespan.org

Copyright Rhode Island Medical Society Mar 2005

Source: Medicine and Health Rhode Island

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