Magnetic Resonance Imaging of the Breast
Christopher P. Goscin, BS, College of Medicine at the University of South Florida; Claudia G. Berman, MD, Robert A. Clark, MD, Radiology Service at the H. Lee Moffitt Cancer Center & Research Institute, Tampa, Fl
[Cancer Control; JMCC 8(5):399-406, 2001. © 2001 Moffitt Cancer Center & Research Institute]
Abstract and Introduction
Background: Magnetic resonance imaging (MRI) has the potential to become a useful adjunct in breast imaging. Contrast-enhanced breast MRI has demonstrated a high sensitivity in the detection of invasive breast cancer. In clinical studies, breast MRI has often altered the course of patient care. Although promising results have been generated, MRI of the breast is currently in a development stage.
Methods: The authors reviewed the literature on the potential indications, sensitivity, specificity, and limitations of MRI of the breast.
Results: Reported advantages of MRI of the breast over conventional imaging techniques include improved staging and treatment planning, enhanced evaluation of the augmented breast, better detection of recurrence, and improved screening of high-risk women.
Contrast-enhanced breast MRI is a sensitive modality for detecting breast cancer, but its variable specificity is a major limitation.
Conclusions: MRI of the breast is emerging as a valuable adjunct to mammography and sonography for specific clinical indications. Additional clinical studies that define indications, interpretation criteria, imaging parameters, and cost effectiveness are needed. A multi-institutional study designed to address these issues is in progress.
Magnetic resonance imaging (MRI) of the breast is a useful adjunct to mammography and sonography when specific clinical indications exist.[1-3] Potential indications for breast MRI include staging and treatment planning, evaluating palpable masses in the silicone augmented breast, detecting recurrent cancer in the posttreatment breast, identifying a clinically or mammographically occult primary tumor in the patient presenting with axillary breast cancer, evaluating the response to chemotherapy, screening in high-risk women including those who are positive for
BRCA1 and BRCA2, and evaluating cases of indeterminate mammographic findings including cases obscured by radiographically dense breasts.[1-4]
An ongoing international, multi-institutional study may offer standardized clinical indications for MRI of the breast and standardized interpretation criteria for breast MR images. Although there is no evidence to support MRI of the breast as a routine screening tool, published studies have evaluated MRI as a diagnostic tool for certain clinical indications.
This article reviews these clinical indications, addresses the sensitivity and specificity of MRI of the breast, and discusses some of the limitations of MRI of the breast.
Staging and Treatment Planning
The American Cancer Society reported that approximately 184,200 new cases of breast cancer were diagnosed and 41,200 individuals died of the disease in the United States in 2000. Properly staging these cancers is essential for appropriate management. Studies have shown that MRI can provide more accurate breast cancer staging than can be provided by conventional imaging techniques.
MRI has repeatedly demonstrated unsuspected multifocal or diffuse disease, which is not seen at mammography.
Identification of the extent and potential multifocality of breast cancer is crucial for determining if a patient is a candidate for breast-conserving therapy as opposed to mastectomy. As the National Surgical Adjuvant Breast and Bowel Project (NSABP) trial demonstrated, the extent of breast cancer at lumpectomy is a major issue as nearly 40% of patients suffered a local recurrence with lumpectomy without radiation.
In a study of 64 patients with biopsy-proven or presumed breast cancer, Orel et al identified 13 patients (20%) with mammographically occult multi-focal or diffuse disease. In a study of 463 patients and 548 histopathologically correlated lesions, Fischer and colleagues concluded that MRI may reveal occult multifocal, multicentric, or contralateral breast cancer and may result in therapy changes.
MRI alone depicted multifocality in 30 patients, multicentricity in 24 patients, and additional contralateral carcinomas in 15 patients.The therapeutic approach was changed in 66 patients (14.3%) because MRI revealed more extensive disease than was noted using conventional imaging techniques along with clinical examination.
Harms and associates found additional cancers in 11 (37%) of 30 patients and suggested that MRI could be used to stage candidates for breast-conserving therapy, to more effectively plan lumpectomy, and to reduce repeat excision surgery. Orel et al determined that MRI has a high (82%) positive predictive value for predicting residual disease after initial excisional biopsy.
In this study of 47 patients, MRI found 9 instances of multifocal or diffuse disease that were not seen on mammography. In patients with extensive disease as determined by MRI, altering management toward mastectomy may be more cost effective and less morbid than multiple excisions that result in mastectomy. If additional lesions can be ruled out by MRI, small, solitary lesions may be treated by lumpectomy alone, thus sparing patients from the morbidity of radiation therapy.[12,13]
Breast MRI may result in improved management and cost effectiveness when deciding between mastectomy and breast conservation with or without radiation therapy.
Evaluation of the Augmented Breast
Approximately 2 million American women have silicone breast implants. In a study of 11,676 women with breast implants, Berkel and colleagues demonstrated that women with silicone breast implants do not have a higher risk of breast cancer compared with the general population.
However, Silverstein et al[16,17] suggested that breast cancer patients with implants present with more advanced stages of breast cancer and have a higher rate of axillary metastases. Also, standard mammographic views have an increased rate of false-negative diagnoses in patients with implants. In a study of 18 patients with implants and breast cancer, standard mammography demonstrated an abnormality in only one patient.
Thus, although breast augmentation is not a risk factor for breast cancer, women with silicone implants are at increased risk for failure to detect cancer at mammography. Silicone implants may obscure mammographic images of the breast tissue and interfere with the interpretation of mammograms, thus hindering detection of breast cancer.[18-20] One study estimated that augmentation mammoplasty obscures 22% to 83% of breast tissue on mammography. MRI has been shown to be more sensitive than mammography for identifying coincidental malignancy in women with breast implants.
The most sensitive study to determine the integrity of silicone breast implants is MRI, followed by ultra-sound and then mammography.[23,24] MRI has produced sensitivities and specificities as high as 94% and 97%, respectively, for identifying implant rupture. Implant rupture can be divided into two types -- intracapsular or extracapsular. The double-lumen implant has an outer fibrous capsule and an inner elastomer shell.
The most reliable sign of intracapsular rupture, which is the most common type of rupture, is the linguine sign, which presents as multiple curvilinear low-signal-intensity lines floating in silicone gel with no extension beyond the fibrous capsule (Fig 2). The linguine sign represents the collapsed elastomer shell. Extra-capsular rupture occurs when both the elastomer shell and fibrous capsule rupture. It can present as gross high-signal-intensity silicone gel external to the fibrous capsule.
MRI sequences for evaluating implant integrity do not use intravenous contrast material, so a contrast-enhanced sequence must be added to evaluate a palpable mass and exclude malignancy in a woman with silicone breast implants. Although technical imaging parameters are beyond the scope of this article, special imaging sequences may be necessary to evaluate the complications of breast implants.
MRI is a valuable option for evaluating a woman with silicone breast implants who presents with a palpable mass that may be related to implant integrity or a parenchymal breast mass.
Evaluation of the Breast After Conservation Therapy
Breast-conserving therapy is increasingly being used in the treatment of breast cancer. Monitoring local recurrence, which occurs in 1%-2% of cases per year, is therefore becoming more important. MRI has proven to be a valuable additional tool for detecting and excluding recurrent tumor 18 months after radiation therapy.
After 18 months, enhancement of areas of radiation fibrosis is rare. MRI has proved to be more sensitive than mammography for detecting recurrence in the posttreatment breast, which may obscure conventional images due to scarring, distortion, and density postsurgical changes (Fig 3).[28,29]
In a study of 105 patients, the specificity of MRI for detecting recurrence was 93% compared with 67% for clinical examination combined with mammography, and the sensitivity of MRI was 100%, compared with mammography alone. MRI may be helpful for detecting recurrence in the posttreatment breast when conventional imaging is indeterminate or negative or when there is a high clinical suspicion for recurrence.
Search for Occult Breast Cancer With Known Metastases
Breast MRI is effective in localizing the site of primary cancer in patients presenting with axillary metastases and a suspected occult primary breast cancer (Fig 4).[31,32] Breast conservation can be offered to the patient if the occult primary tumor is solitary and well visualized. If MRI cannot identify the occult primary, then breast conservation is not an option.
Using MRI, Morris et al identified 9 of 12 occult primary breast tumors. Using MRI, only one of these 12 patients had multiple enhancing lesions that necessitated mastectomy. Two patients had no identifiable tumor on histopathologic analysis at mastectomy, and MRI findings were negative in both cases. Eight patients were candidates for breast conservation therapy.
Multiple reports have supported the value of MRI for identifying occult breast cancer in patients with known metastases and negative mammograms and physical examinations.[33-36] Breast MRI in this situation may offer patients the option of breast conservation instead of mastectomy.
Ann's NOTE: I have had two MRI's of the chest wall. It proved to be the only way to assess local recurrence there. Sonogram did NOT work.
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