Magnetic Resonance Magnetic resonance imaging may be of value in assessing breast lesions of an indeterminate Imaging nature detected by clinical and mammographic examination or occurring in patients who have implants (58). Both MRI and positron emission tomography (PET) are used to identify occult lesions, and MRI is increasing in popularity as a means of imaging the breast (58–60). It tends to be highly sensitive but not specific, leading to biopsies of benign lesions. Image enhancement with gadolinium discriminates between benign and malignant lesions with varying degrees of accuracy.
Several roles are proposed for breast MRI. The lack of radiation exposure makes MRI theoretically an ideal method for screening of healthy women, but widespread use is not cost-effective. Focal asymmetry is usually benign but can represent a malignancy. MRI may help identify those patients with focal asymmetric areas who should undergo biopsy. A scar can easily be distinguished from recurrent tumor based on the evaluation and diminution of the scar over time. Some scars do not resolve rapidly and are confused with cancer or, more commonly, with recurrent cancer after breast-conserving surgery and whole breast irradiation. Ideally, such cases are evaluated with MRI, sometimes obviating the need for biopsy. MRI is extremely useful in identifying silicone released by ruptured breast implants in patients with augmented breasts (Fig. 21.3). In patients with implants, MRI with gadolinium may be performed to detect breast cancer even if silicone release is not suspected. There may be a role for MRI in evaluation of specific conditions. It is used for the following indications:
Stage tumor to rule out multicentric disease.
Differentiate postoperative scar from recurrence after breast-conserving surgery.
Figure 21.3 Mammography shows implant and extracapsular free silicone (arrow).
Find a lesion seen in only one view of mammogram.
Evaluate positive axillary nodes in the presence of negative mammogram and clinical breast examination results.
Rule out silicone implant rupture.
Assess focal asymmetry.
Detect additional ipsilateral and contralateral cancers.
Evaluate the effect of neoadjuvant chemotherapy.
The American Cancer Society recommends annual MRI screening for women who are high risk (greater than 20% lifetime risk) and consideration given to women with moderate risk (15% to 20% lifetime risk) (61). A study from the Netherlands in high-risk women reported 71% sensitivity for MRI compared with 17.9% for clinical breast examination and 40% for mammography (62). The International Cooperative Magnetic Resonance Mammography Study will help identify the advantages and limitations of MRI. At present, MRI should be considered only after conventional imaging is performed; it should not be used as a screening tool or a substitute for mammography or biopsy. Centers that perform MRI should have the ability to perform MRI-guided biopsies of lesions detected with MRI only and that are not visible with mammogram or ultrasound.
PET scanning is a diagnostic modality that assesses the metabolic activity of tumors. Radioactive ﬂuorodeoxyglucose (FDG) is an analogue of glucose that is metabolized by tissues of high metabolic activity. Although not specifically approved for the initial diagnosis of breast cancer or for staging the axilla, it can be useful in patients with advanced disease (59,63). This technique is used to identify occult breast lesions with positive axillary lymph nodes (59).
Breast Tissue Evaluation: Histology and Cytology