Magnetic resonance imaging (MRI) of the breast is emerging as an important tool in women's imaging. In the patient with breast implants, MRI provides an essential method for visualizing implants and their complications. In the patient with breast cancer, MRI is rapidly becoming a practical adjunct to mammography and ultrasonography. The imperfections of mammography have encouraged the growth and evolution of MRI indications.
received her medical degree from the Mayo Medical School in
Rochester, MN in 1998. She is a third-year Radiology Resident at
the University of Utah Hospital, Salt Lake City, UT. Dr. Oh plans
to complete a Women's Imaging fellowship after her residency.
Magnetic resonance imaging (MRI) of the breast is
emerging as an important tool in women's imaging. In the patient
with breast implants, MRI provides an essential method for
visualizing implants and their complications. In the patient with
breast cancer, MRI is rapidly becoming a practical adjunct to
mammography and ultrasonography. The imperfections of mammography
have encouraged the growth and evolution of MRI
Women's health is increasingly recognized as an important part
of preventative medicine, with breast cancer detection and
treatment at the forefront. With approximately 180,000 women
diagnosed with breast cancer annually, it is the leading cause of
death among women aged 40 to 55 years.
Mammography has been the traditional screening tool for breast
cancer, supplemented with ultrasonography for problem solving. It
remains, however, an imperfect screening tool. Therefore, magnetic
resonance imaging (MRI) is becoming increasingly popular for use in
the clinical setting, with indications ranging from detection of
implant failure to breast cancer evaluation.
Imaging breast implants
Breast implants are utilized for many different reasons, from
self-image to breast reconstruction following mastectomy.
Mammography does not provide the sensitivity needed for adequate
visualization of implants; however, MRI does provide a viable
alternative for more accurate evaluation. This is particularly
important for the evaluation of patients with breast pain,
irregularity, or concern over potential health-related
complications associated with silicone leakage. Though no direct
link has been proven between systemic disease and breast implant
rupture, many patients would rather remove the prostheses than take
that risk. However, many insurance companies will not pay for the
removal of implants unless there is a documented complication, such
as rupture. Accurate documentation of the breast implant is
required in such cases, and MRI is the most effective modality in
the diagnosis of implant rupture.
Morgan et al
prospectively evaluated 345 breast implants in 185 women, and found
that 100 implants showed evidence of rupture on MRI. Of these, 73
were subsequently removed surgically and correlated with pathologic
findings of rupture. Similar to other reports in the literature,
MRI demonstrated a sensitivity of 84% and a specificity of 92% for
the detection of rupture in the removed implants.
Ideally, a bilateral breast surface coil is used for comparison
of sides in a patient with two implants. The patient is placed
prone in the magnet during the study. In general, a typical
protocol will include a T2-weighted fast-spin echo (FSE) sequence
followed by a fat-suppressed inversion recovery sequence in the
axial, coronal, or sagittal planes. Silicone-only sequences can be
performed with the use of an inversion recovery FSE sequence with
water saturation, or a three-point Dixon technique.
Selective silicone imaging can also be achieved with T1-weighted
sequences utilizing silicone suppression (taking advantage of the
difference in T1 relaxation time of silicone).
The normal implant
Most implants are single lumen, with an outer silicone elastomer
shell filled with silicone gel. The less common double-lumen
implant has an inner lumen containing silicone gel, surrounded by
an outer lumen with saline. Both types of outer shells may be a
smooth or textured silicone elastomer. Implants are placed in the
sub-glandular or subpectoral positions. Reactive fluid around the
textured implant is considered normal.
The implant contour should be smooth, but often with folds and
invaginations. These are normal radial folds if they are at the
margins of the implant and are thicker than the linear low-signal
lines created by intracapsular rupture. Radial folds are generally
thicker because of the two opposing layers of silicone elastomer,
in comparison to the single layer seen in intracapsular rupture
(figure 1). Additionally, radial folds frequently are perpendicular
to the implant surface. Most patients develop a fibrous capsule
surrounding the implant, caused by a foreign-body response, which
appears as a rim of T2-hypointense tissue surrounding the silicone
or saline implant.
The ruptured implant
There are two types of rupture, intracapsular and extracapsular.
Intracapsular rupture is more common, with a breach of the outer
elastomer without leakage beyond the fibrous capsule. Thin,
hypointense lines within the high signal implant on T2-weighted
images characterize the free-floating ruptured elastomer shell
(figure 2). Silicone is seen on both sides of the elastomer shell
as it collapses within the fibrous capsule. This is the "linguine
sign" as originally reported by Gorczyca et al,
and is the most reliable sign for intracapsular rupture.
Extracapsular rupture may be seen on mammography,
ultrasonography, or MRI. It is defined as leakage of silicone
outside of the fibrous capsule. Extracapsular silicone is bright on
silicone-only sequences or T2-weighted images with water
saturation, and dark on T1-weighted silicone suppressed sequences
(figure 3). Silicone can be seen anywhere in the adjacent breast
parenchyma, axillary lymph nodes, or even within the pectoral
Siliconomas are the result of a host foreign body reaction, and can
be seen on T2-weighted fat-suppressed MRI as hypointense
Imaging breast cancer
MRI is rapidly becoming incorporated in the field of breast
cancer imaging. As the most sensitive modality for imaging the
breast, many potential uses have been, and continue to be,
Given that breast MRI is still evolving, there is no universally
accepted imaging protocol. In general, high field strength is
thought to be advantageous, and specialized breast coils are
required to increase temporal and spatial resolution. Bilateral
breast coils are used for a comprehensive view of the breasts, to
permit comparison of both sides. Single breast coils may also be
used to gain better spatial resolution and an increased
signal-to-noise ratio. T1-weighted images are obtained for
visualization of the anatomy, and T2-weighted images for
characterization of cysts and fibroadenomas. Fat-saturation
following dynamic contrast administration is required to clearly
delineate enhancing lesions from fat on post-gadolinium images.
Fat-saturation may be active (prior to contrast administration)
with a saturation pulse, or passive, using subtraction of pre- and
Both methods have their drawbacks. Active fat-saturation can result
in incomplete fat suppression. Passive techniques are susceptible
to motion artifacts between the pre- and postcontrast images,
causing the subtraction to be inaccurate. Other technical issues
include the choice of two-dimensional versus three-dimensional
volume acquisition, field of view, and the tradeoff in
signal-to-noise ratios with volume averaging.
Morphology is best visualized with high-resolution MRI, and can
help distinguish benign from malignant lesions,
with the margins of a mass most helpful in differentiating
malignant from benign. Spiculation or irregular margins, similar to
mammography, suggest malignancy (figure 4). Peripheral rim
enhancement is also associated with cancer, with a positive
predictive value (PPV) as high as 93% for rim enhancement occurring
with spiculated or irregular margins.
However, only 36% to 65% of cancers have this feature, therefore
the negative predictive value (NPV) is not as high.
Clumped and/or linear enhancement is highly predictive of ductal
carcinoma in situ (DCIS) (figure 5).
Features of benign disease include smooth or lobulated borders,
absence of enhancement, nonenhancing internal septations, and low
Focal masses with nonenhancing internal septations are benign in
>90% of cases, the most common lesion being a fibroadenoma.
Even more fundamental than lesion morphology, Harms et al
initially used contrast in conjuction with a special fat supression
technique to improve spatial resolution (RODEO [rotating delivery
of excitation off resonance]). This allowed clear delineation of
enhancing tumors from adjacent fat. A lesion was considered
positive if its signal intensity was higher than that of breast
parenchyma on static postcontrast images. Although the initial
study does not address lesion morphology, they report a sensitivity
of 94% and specificity of 37%. Nunes et al
recently published an update on a tree-shaped interpretation model
based on architectural findings, developed to increase the
sensitivity and specificity of breast MRI. Confirming their earlier
work, they report a sensitivity of 96%, specificity of 75% to 80%,
and NPV of 96% for their model.
Intravenous gadolinium enhancement provides a sensitive, but not
specific, tool for the evaluation of breast lesions. Therefore,
multiple methods have been developed to increase specificity.
Kaiser et al
were the first to suggest rapid sequential imaging with limited
spatial resolution. The group further proposed a quantification, to
normalize enhancement with respect to the baseline signal
intensity. In their model, enhancement is based on the equation:
[(SIpost SIpre)/SIpre] * 100. This equation has become the
standard formula for measuring lesion enhancement. Kaiser et al
found that malignant lesions doubled their signal intensity within
the first minute after contrast; however, DCIS may not enhance as
rapidly and therefore can create false negative results.
Gilles et al
had a similar approach, suggesting that early enhancement indicates
malignancy. Their approach found a sensitivity of 95% and
specificity of 53%. These theories were based on the fact that
malignancies enhance before normal glandular tissue, which is
typically more delayed. However, Kuhl et al
have since shown that normal glandular tissue can enhance during
the menstrual cycle, with 73% of enhancing lesions resolving
completely during follow-up. Some of these lesions even
demonstrated initial enhancement rates beyond the malignancy
threshold value (>80% increase in the first minute).
Boetes et al
used the single-section technique with high temporal resolution to
image, and found a sensitivity of 95% with a specificity of 86%.
This group further associated a centripetal pattern of enhancement
with malignant lesions, while centrifugal was more likely benign.
To further clarify enhancement characteristics, Kuhl et al
observed that beyond the initial early enhancement, the time-signal
curve could be an important criterion in differentiating malignant
from benign lesions. This group classified lesions according to the
curve types. Type Ia curves are continuously increasing over the
dynamic period, type Ib curves increase and flatten late
postcontrast. Type II is an initial upstroke followed by a plateau.
Type III has an initial upstroke with an abrupt cut off and signal
washout in the intermediate post-contrast period (ie, 2 to 3
Type III curves have a likelihood of breast cancer in 87% of cases,
whereas type I curves have a likelihood of only 6%.
Type II curves are seen in both malignant and benign lesions, but
at a ratio of 3:2 malignant to benign.
These curves help to distinguish normal enhancing glandular tissue
from malignancy, since normal parenchyma does not typically
demonstrate the washout phenomenon after initial enhancement.
Kuhl et al
also concluded, however, that type I curves can be seen in lobular
or scirrhous ductal cancer and the lack of a washout phenomenon
cannot be used to exclude cancer.
In an attempt to merge the issues of temporal versus spatial
resolution, Kuhl et al utilizes the following guidelines
: Initial evaluation is made for lesions with significant
enhancement, and those with suspicious morphology are biopsied. If
the morphology is indeterminate or benign, the time-signal curve is
reviewed. Lesions with type III curves are sent for biopsy, while
those with type I or II curves are followed up. If a lesion has
mild enhancement, management decisions are based on lesion
morphology to include lobular carcinoma and DCIS. In their
guidelines, rim enhancement leads to biopsy, while lesions with
nonenhancing internal septations are diagnosed as fibroadenoma.
With this type of interpretation, integration of both temporal and
spatial data may further aid in the diagnosis of malignancy.
A consistent terminology system would facilitate accurate breast
MRI interpretation, and would provide standardized descriptors
similar to the Breast Imaging and Reporting and Data System
(BI-RADS) for mammography. To this end, the Breast MRI Lexicon
Working Group is developing a system of terminology as new research
comes to light. Both morphology and kinetic findings should be
included in a breast MRI report, with a final recommendation to
convey the level of suspicion to the referring clinician.
in conjunction with the Breast MRI Lexicon Working Group, proposed
a table of descriptors (Table). This is still a work in progress,
but is an initial attempt to standardize breast MRI reporting.
Clinical breast MRI indications
Despite ongoing research, many controversies remain. Consistent
acquisition techniques are not yet established, and once the images
are acquired, a formal reporting system does not yet exist. The
mammography BI-RADS reporting system is inadequate for the
intricacies of MRI, as it does not include contrast-enhancement
characteristics. Furthermore, once a lesion is identified, there is
a lack of consensus on the exact criteria required to diagnose
breast cancer. Given the many unresolved issues and wide variety of
imaging techniques, breast MRI is usually performed only in
specific clinical settings. Other than for breast implant
evaluation, there is no data to support the use of MRI for the
general screening population, especially given the cost
differential between MRI and mammography.
The equivocal mammogram
Mammography is an imperfect screening tool. MRI of the breast
can help increase the sensitivity of lesion detection. Although
breast MRI is very sensitive in the search for malignancy, its
reported specificity varies widely in the current literature, from
37% to 98%.
This lack of specificity is caused by the overlap in the appearance
of enhancement in benign and malignant lesions. Additionally,
normal breast parenchyma may enhance with a similar pattern to
malignant lesions depending on hormonal fluctuations.
Higher specificities are associated with those protocols evaluating
dynamic contrast uptake.
Lee et al
studied 86 lesions where equivocal findings were present on
mammography, and concluded that breast MRI can be a useful adjunct
in managing the problematic mammogram. They acknowledged, however,
that false negatives could occur in cases of DCIS, invasive lobular
carcinoma, and invasive ductal carcinoma.
Also, they concluded that MRI should be used as an adjunctive tool
only, when mammography and sonography are inconclusive.
Breast cancer staging and preoperative planning
The imperfect sensitivities of mammography and ultrasound have
led to an attempt to use MRI to more accurately stage breast
cancer, with a secondary benefit of allowing for preoperative
planning. MRI can delineate tumor margins, assess involvement of
adjacent structures, and screen for multifocal lesions (figure 6).
Accurate preoperative planning may mean the difference between
breast conservation surgery and mastectomy. Breast MRI may reveal
unsuspected multifocal, multicentric, or contralateral breast
carcinoma. Fisher et al
studied the use of MR in a group of 463 patients, each with a
previously discovered breast abnormality diagnosed on mammography,
ultrasound, or clinical examination. Therapy was altered correctly
in 14.3% of patients with a known breast abnormality, because MR
imaging showed more extensive disease than had been appreciated
initially. These included multifocal, multicentric, or synchronous,
contralateral carcinomas. The rate of false positive findings was
low at 3.5% (16 of the 463 patients had a lesion biopsied
unnecessarily). DCIS poses a known limitation, however, because the
sensitivity of MRI is low for detection of DCIS; 21 of their 30
false-negative findings were DCIS on histology.
Axillary adenopathy with an unknown primary cancer
Although the incidence is low, at 0.3% to 1.0% of operable
breast cancers, axillary adenopathy with an occult primary cancer
can present a significant problem for clinicians.
Patients who have a negative clinical examination and negative
mammogram are traditionally treated with mastectomy and axillary
Breast MRI has been shown to be very sensitive in the detection of
occult breast cancer in patients with malignant axillary
MRI can provide more accurate localization of the primary
malignancy, and can offer information on staging and treatment
Screening for high-risk cohorts
Women who have the BRCA1 or BRCA2 gene or a strong personal or
family history of breast cancer have an increased risk for the
development of the disease. These women are a special group and are
offered earlier education, clinical breast exams, and screening
mammography than the general population.
Concerned patients sometimes consider aggressive prophylactic
treatments such as mastectomy. Breast MRI is a promising
alternative to conventional evaluation, since its high sensitivity
may allow it to be used as an effective screening tool in these
women. Many of these patients are younger than the typical
screening population, and interpretation can be difficult because
of normal parenchymal enhancement, which is cyclical and related to
Additionally, incidental enhancing lesions, which are unlikely to
be malignant, can be seen in up to 29% of imaged patients.
In one study, the incidental lesions found were mostly seen in
women who were younger, were premenopausal, or had dense breast
Despite these challenges, early results indicate that breast MRI
may be superior to mammography and ultrasound for the screening of
women at high risk for hereditary cancer.
Future directions of breast MRI
Breast MRI is emerging as a valuable adjunct to mammography and
ultrasound, and can be used to detect primary breast cancer with a
higher sensitivity as discussed above. What happens when a
suspicious lesion is identified on MRI that was not seen on the
diagnostic mammogram or ultrasound? Redirected ultrasound is one
alternative, to permit an ultrasound-guided localization. A second
alternative is MRI-guided localization using MRI-compatible
stereotactic wires, with subsequent surgical resection.
The pitfall with this approach is the inability to confirm lesion
removal in the lumpectomy specimen. More promising is the
core-needle biopsy, using MRI-compatible guns to allow tissue
sampling. This, like core-needle biopsy under mammographic or
ultrasound guidance, can be used to avoid the morbidity and costs
of surgical resection. Kuhl et al
reported a series of 78 lesions, with 99% of the lesions yielding
sufficient material for histologic diagnosis, and a diagnostic
accuracy of MRI-guided bore biopsy of 98%. Their technique includes
a 14-gauge coaxial needle, with verification of placement on a
T2-weighted sequence, possibly using a second contrast-enhanced
series if the lesion was not adequately visualized.
Difficulties included the "vanishing target" phenomenon, in which
the core-biopsy needle obscures the lesion.
MRI-compatible vacuum-assisted biopsy has also been found to be a
reliable and accurate biopsy method.
MR spectroscopy is already used for evaluation of brain masses,
to increase the specificity of MRI. Spectroscopy in the breast has
been studied for the same purpose. In a study by Button et al,
MR spectroscopy and relative regional blood volume mapping (rRBV)
were used to evaluate patients who had rapidly enhancing lesions.
They showed that of the 13 lesions with a prominent choline peak
and "enhanced" rRBV, all were shown to be malignant tumors. The
other 11 patients who had no choline or "enhanced" rRBV detected
had pathologically benign lesions. Two fibroadenomas also
demonstrated a detectable (but not prominent) choline peak.
However, this group's research indicates that breast MR
spectroscopy can be used to improve specificity.
At the 2001 Radiologic Society of North America meeting, Sinkus
addressed one of the newer techniques of breast cancer diagnosis.
This group presented their work on dynamic MR elastography, used to
assess the visco-elastic properties of tissue. The technique is
performed following routine contrast-enhanced imaging, and
illustrates different values of "stiffness" for different tissues.
Discrepancies in breast cancer isotropic and anisotropic elastic
properties potentially can be used to improve the specificity of
Breast MRI is becoming increasingly practical in the clinical
setting, with advances in both technology and interpretation
techniques. There are innumerable potential uses for breast MRI,
with a few of the more extensively studied clinical indications
discussed above. Other potential clinical applications include
chemotherapy follow-up, radial scar evaluation, and postoperative
residual tumor scanning. Research continues on new imaging
techniques such as MR spectroscopy and elastography in the hope of
increasing specificity. Many more clinical indications are expected
to arise as our knowledge expands and we maximize the information
provided by breast MRI.
The author would like to thank Dr. Maryellyn Gilfeather, Dr.
Anne Kennedy, and Dr. Kevin Moore for their help in reviewing this