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4.2 MRI (Magnetic Resonance Imaging)

Updated July 2009

Clinical Indications for Breast MRI

Introduction

Although MRI has advanced some areas of oncologic imaging, as well as neurological and musculoskeletal imaging, the transformation is less complete in breast imaging where other well established and less expensive techniques can often provide necessary information.

The purpose of these recommendations is three-fold, in the absence of substantial randomized controlled trial data on the usefulness and value of breast MRI:

  • To provide education and awareness to ordering physicians on the potential uses and pitfalls of breast MRI.
  • To help radiologists and ordering physicians utilize the resource effectively in the appropriate clinical settings.
  • To encourage collaboration in useful clinical research projects for the above.
Mammography is the standard breast imaging modality against which other modalities can be judged since there is an extensive body of trial data and a long period of surveillance follow-up. MRI has not yet met the challenge of proving that it can help to decrease mortality, recurrence or impact of treatment. Nor do we know its true positive predictive value. Specificity is variable, particularly in premenopausal women where incidental enhancing lesions are often identified.  There is currently no literature of level 1 evidence to support the use of MRI for any specific indication. It is not certain which women or imaging questions will be best served by this modality and at what costs.

Breast MRI should be used in a problem-solving mode only after high quality mammography and ultrasound have been carried out. As well, it should be done by a radiologist with expertise in breast MRI, as these images require specialized knowledge for interpretation.

MRI sensitivity rates for the detection of invasive breast cancer are estimated to be as high as 95-100%, which compares well to mammography at 85%. However, a significant limitation is specificity, which is highly variable ranging from 37-97%. Like all breast imaging studies, breast MRI must be correlated with other imaging findings in light of clinical findings.

The Breast Tumour Group (of BC Cancer) has discussed these indications which have been developed by Drs. Patricia Hassell and Moira Stilwell. The consensus was that as there is not level one evidence we cannot claim that these are standard Guidelines but are suggested clinical indications and are divided into those that are more established in terms of benefit, those that are not established but may be indicated for specific patients and those that should not be routinely recommended. MRIs within the context of clinical trials should be considered outside of these indications.

Other than cancer indications, breast MRI can be utilized to evaluate silicone implants.

Evaluation of silicone implants

MRI has been shown to be more reliable than CT, ultrasound or mammography for assessment of rupture/integrity/complications of silicone breast implants. The mean sensitivity was 38% for mammography, 59% for ultrasound and 78% for MRI.   

4.2.1 Recommended Uses of Breast MRI for Cancer (highest level of evidence)

1. Screening of high-risk patients – patients with hereditary cancer risk

In patients who have tested positive for mutations of the BRCA 1 and 2 genes or who are at high risk of breast cancer due to a family history of the disease, MRI has been shown to detect cancers before mammography, ultrasound or clinical examination could detect the malignancy. The greater incidence of high-grade invasive malignancies in this high-risk group does provide the rationale for using MRI as a screening modality in known mutation carriers (including, but not restricted to, BRCA1 and BRCA2). In these women, screening is done using annual imaging with mammography and MRI concurrently or alternately. In British Columbia, the role of breast MRI screening in high-risk women with a strong family history of breast cancer but no known gene mutation is under review. Studies have suggested that ultrasound may also have a role in following these women but recent literature does not support continued ultrasound screening in asymptomatic high-risk women. As scientific evidence concerning the role of MRI in patients with biopsy proven ADH or LCIS has shown that although more cancers are detected, this has not yet translated into decreasing mortality, MRI is not used in this situation.

2. Evaluation of occult breast cancer

In patients with an occult primary presenting with axillary lymphadenopathy or Paget's disease, MRI has been shown to identify the primary in many patients, thus allowing for conservative surgery rather than mastectomy. This is not indicated if mammography clearly shows a suspicious lesion. Trials are ongoing studying the impact of MRI on this group of patients.

B. Possible Uses of Breast MRI

These include a number of clinical scenarios where other imaging modalities have not provided adequate assessment and where a further evaluation with an MRI showing more disease may impact and/or change management.

1. Evaluation of local extent of breast cancer

MRI can be useful in pre-operative assessment of local disease extent when this is unclear either by physical examination, mammography or ultrasound.  Mammography is more accurate in determining the size and additional sites of malignancy. However, not all women benefit from having an MRI as 8% underwent additional biopsy or surgery for findings detected on the MRI which subsequently proved to be benign. This may be particularly indicated in lobular carcinoma where mammography may be less sensitive and where there may be multicentric disease.

2. Positive margins – post segmental resection

MRI can be useful in determining the extent of residual disease when margins are positive and the mammogram is not helpful. In the majority of cases however, as further surgery is indicated, it will not necessarily impact on treatment. 

3. Post surgical scar vs. recurrent tumor

In cases in which mammography and ultrasound can not conclusively confirm suspected recurrent disease, MRI can be helpful. Breast tissue can show enhancement for up to 18 months following radiation therapy, however. In many of these situations, a biopsy will be necessary to rule out disease and may be a preferable diagnostic test.

4. Problem mammogram

MRI can be useful in a small number of patients when there is an equivocal mammographic finding, i.e. a possible architectural distortion, or mass seen only in one view, in whom there is no ultrasound or clinical correlate. Many of these patients have heterogeneously dense breasts. 

5. Response to chemotherapy

MRI has been used to monitor treatment response to neoadjuvant chemotherapy in patients with locally advanced cancer. There is controversy over the ability of MRI to determine complete or partial response to treatment. Changes in tumor vascularity/enhancement appear to explain changes in functional dynamic contrast assessment and can be seen after only one cycle of chemotherapy. MRI tends to underestimate residual disease. At this time this should only be used in association with a clinical trial.  

4.2.2 Inappropriate Use of Breast MRI

1. Screening of general population

At present there is no data to support the use of MRI as a screening tool. To date, there are no studies demonstrating decreased mortality by the use of screening MRI. Not all cancers seen on mammography can be identified in MRI. This is especially true for DCIS. 

2. Differentiation of benign vs malignant lesions

Because of an overlap between the enhancement and morphological characteristics of benign and malignant lesions, MRI cannot be used as a substitute for biopsy.

SOURCE: 4.2 MRI (Magnetic Resonance Imaging) ( )
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