Magnetic resonance imaging (MRI) of the breast has been around since the 1980s but has only become more widely utilized in the past few years. This is predominantly due to the development of more standardized protocols for breast MRI, advances in equipment and image quality and increased experience of interpreting radiologists.
The ability to produce high-contrast three-dimensional images is one of the advantages of MRI over mammography. The superior contrast resolution of MRI is further accentuated by the use of intravenous contrast, which facilitates the evaluation of lesions as small as 3 mm. MRI is basically a study of vascularity. Breast cancers form new blood vessels that leak. The rapid uptake and washout of contrast from these leaky vessels helps the radiologist distinguish breast cancers from benign lesions. Morphology of the area of contrast enhancement is also a critical factor in assessing benign versus malignant lesions.
A breast MRI is performed with the patient lying prone with her breasts positioned with minimal compression in a dedicated breast-imaging coil. The prone position helps decrease motion from breathing. To enhance image quality, it is crucial that the patient remains completely still during the study. Central Baptist Hospital utilizes the Sentinelle Vanguard 8 channel breast coil, which is designed to optimize patient comfort while producing images of the highest quality.
An IV is required for gadolinium-based contrast administration. All patients receive contrast unless they are being scanned solely for evaluation of silicone-implant rupture. Unlike mammography, minimal breast compression is utilized as blood flow should not be impeded during imaging. Bilateral breast studies are always performed. The average exam lasts 30 minutes. If possible, breast MRI should be performed during days seven to 14 of the menstrual cycle when the breasts are the least “active.” Hormone replacement therapy should be discontinued at least 30 days prior to the MRI study.
Breast MRI is ideally performed at a facility that has MRI-guided biopsy capability. Many MRI lesions that require a biopsy can be found with focused ultrasound examination and biopsied with ultrasound guidance. However, some lesions will not be visualized with ultrasound and will require MRI guidance for the biopsy. Central Baptist’s Sentinelle breast coil not only optimizes patient comfort and image quality but also provides both medial and lateral biopsy access.
Many facilities do not interpret or perform biopsies on outside breast MRI cases. Reading outside MRI studies is a challenging endeavor for the radiologist because critical images are often not available for review due to differences in software. Unfortunately, outside MRI cases requiring intervention are typically repeated.
Breast MRI may be utilized for diagnostic purposes or as a screening modality for high-risk patients. More traditional indications for breast MRI include evaluation of possible silicone implant rupture; preoperative assessment of patients with recently diagnosed breast cancer; evaluation of residual disease in patients with positive surgical margins at lumpectomy; monitoring response to neoadjuvant chemotherapy; and assessing occult malignancy (i.e., biopsy-proven metastatic disease to the axillary lymph nodes with no mammographic or ultrasound evidence of breast cancer). MRI is also the best imaging modality for evaluating possible recurrence of carcinoma at the site of a prior lumpectomy. Other cases that may warrant MRI evaluation after appropriate mammographic and sonographic work-up are patients with nipple discharge and patients with a discrete palpable abnormality but no mammographic or ultrasound correlate.
When using MRI in a patient who has recently been diagnosed with breast cancer, the radiologist is evaluating the extent of disease in the ipsilateral breast and screening the contralateral breast. MRI is helpful for evaluating multifocal and multicentric disease in the ipsilateral breast. MRI is also the best imaging modality for assessing pectoralis muscle involvement when the cancer is close to the chest wall. Because both breasts are routinely imaged, the contralateral breast can also be evaluated for malignancy. Unsuspected breast cancer is identified in the contralateral breast in 3 percent to 24 percent of patients. Synchronous bilateral breast cancers are more common in patients with invasive lobular carcinoma. Preoperative breast MRI alters surgical planning in approximately 15 percent to 20 percent of patients. Patients who were originally scheduled for a lumpectomy may truly need a mastectomy based on the extent of disease noted on the MRI. The primary goal of preoperative breast MRI is to aid the patient in achieving a one-step surgery.
The American Cancer Society (ACS) issued an updated statement regarding recommendations for screening breast MRI in the March/April 2007 issue of the ACS journal CA: A Cancer Journal for Clinicians. Annual screening MRI along with annual screening mammography was recommended for high-risk patients as determined by the following criteria:
• Patients with a calculated lifetime risk of developing breast cancer of 20 percent or greater based on risk assessment models that look at both personal and family history.
• Patients with BRCA1 or BRCA2 gene mutations.
• Patients with a first-degree relative (parent, sibling, child) who has a BRCA1 or BRCA2 gene mutation, even if the patient has not been tested.
• Patients with a history of chest-wall radiation between the ages of 10 and 30.
• Patients with Li-Fraumeni syndrome, Cowden syndrome or Bannayan-Riley-Ruvalcaba syndrome.
For those women whose lifetime risk falls between 15 percent to 20 percent (intermediate risk), the ACS states there is not enough evidence to make a recommendation for or against annual screening breast MRI. The decision to undergo breast MRI screening should be based on a discussion between the patient and her referring physician. Patients whose overall risk might fall between 15 percent and 20 percent include those with a prior history of biopsy-proven atypical ductal hyperplasia (ADH), atypical lobular hyperplasia (ALH) or lobular carcinoma in situ (LCIS) and patients with a mammographically dense breast pattern. Many patients who have previously been diagnosed with breast cancer will fall into the intermediate risk category.
Screening breast MRI is not recommended for women whose lifetime risk of developing breast cancer is below 15 percent. Mammography remains the best overall screening exam for these patients. MRI is more sensitive than mammography but also results in more false positive results. False positive exams lead to a large number of unnecessary biopsies and increased patient anxiety. Mammography remains the most cost-effective screening tool and the most reliable modality for detecting breast calcifications, which may indicate the early stage of breast carcinoma or ductal carcinoma in situ.
In summary, breast MRI plays a complimentary role in relation to mammography. MRI can be used as a diagnostic tool or for screening high-risk patients. High-risk status may be determined by a genetic counselor or the patient’s referring physician using a variety of risk-assessment models such as the Gail model, Claus model, BRCAPRO model or Tyrer-Cuzick model. It is important to remember that patients who meet the ACS’s criteria for annual screening MRI will still need to undergo yearly screening mammography.
By Molly Hester, M.D. and Angela Moore, M.D.
“American Cancer Society Guidelines for Breast Screening with MRI as an Adjunct to Mammography,” published in the March/April 2007 CA: A Cancer Journal for Clinicians (Vol. 57, No. 2:75-89). First author: Debbie Saslow, Ph.D., American Cancer Society.
“MRI Evaluation of the Contralateral Breast in Women with Recently Diagnosed Breast Cancer,” published in the March 29, 2007 New England Journal of Medicine (Vol. 356, No. 13:1295-1303). First author: Constance D. Lehman, M.D., Ph.D., University of Washington Medical Center, Seattle.
Breast MRI: Diagnosis and Intervention, Morris, Elizabeth A., and Liberman, Laura, Springer, 2005.