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Ashley K. Gist, MD
Syllabus: Breast Imaging
Third Year Medical Student Radiology Course
Breast Imaging
Breast Anatomy
The breast is a modified skin gland. Breast tissue lies between the clavicle and the 6th to 8th ribs
and can be found from the sternum to the mid-axillary line. Breast tissue lies on top of and lateral
to the pectoralis major muscle (and frequently wraps around the lateral margin of the muscle).
There are anywhere from 6 to greater than 20 lobes or segments within the breast. A lobe is
defined by the major lactiferous ducts that open on the nipple. Each lobe is like a tree whose
leaves, branches and trunk are hollow and conducts milk from the lobules to the nipple. The
lobule consists of multiple glandular acini (like fingers of a glove). With the terminal duct, the
lobule is called the terminal duct lobular unit. The TDLU is actually the most proximal portion
of the duct system if direction is the flow of breast secretions (milk).
The breast is held together by connective tissue that form sheets of tissue referred to as Cooper's
ligaments. Fat is interspersed throughout the breast as well as surrounds the breast tissue
subcutaneously and retromammary
The duct is lined by a single layer of cells, which are surrounded by myoepithelium and
basement membrane. Carcinomas contained within the ductal system are termed in situ.
Carcinomas that breach the basement membrane are termed invasive.
Breast Development
The breast tissue is of ectodermal origin (same as skin glands). The breast develops from the
mammary ridges, which extend from the axilla to the inguinal region. The middle portion of the
upper third of the mammary ridge persists normally to form the breast bud on the chest wall.
Failure of portions of the remainder of the ridge to involute can result in accessory breast tissue
anywhere along the milk line. The most common area for accessory breast tissue is the axilla.
The most common location for accessory nipple is the anterior superior abdominal wall just
below the usual breast location.
Screening Mammography
Why do we screen?
Each year, more than 210,000 women are diagnosed with invasive breast cancer in the U.S.
Additionally, 35,000 cases of DCIS are diagnosed annually. The rate of deaths due to breast
cancer began to decrease in 1990 and has continued to decrease despite increasing annual
incidence. Approximately 40,000 women still die annually from breast cancer. Early detection,
currently, is the best hope for mortality reduction.
Screening mammography is the evaluation of asymptomatic women, who have no overt signs or
symptoms of breast cancer. Screening is performed
in an effort to detect disease earlier in its growth, at a time when cure is still possible.
Screening mammography should be performed annually, beginning at age 40. ACS
guidelines also include annual clinical breast exam and monthly self breast exam. Ideally, the
annual screening mammogram should follow the annual clinical breast exam.
There is no specific recommendation as to what age screening should be discontinued. Whether
to screen older women should be individualized, balancing the benefits of screening against the
life expectancy of the individual and competing causes of death.
In very high risk women, with a first degree relative diagnosed with premenopausal breast
cancer, screening should begin 5-10 years earlier than the age at which their relative was
diagnosed.
Mammography alone can miss 10-15% of cancers, therefore it should not be used to exclude
cancer, especially in the presence of a clinically significant abnormality. Women should be
reminded that a negative screening mammogram does not guarantee freedom from breast cancer,
and they should bring any breast changes to the attention of their doctor.
Radiation risk for the breast decreases with age. The risk of radiation exposure of the breast
becomes important below the age of 30. The benefit of early detection and mortality reduction
out-weigh the theoretical risk of detrimental effects of the radiation exposure.
Technical Considerations
The standard screening mammogram consists of 4 images, 2 views of each breast. The
projections obtained are named for the direction of x-ray travel, craniocaudal (CC view) and
mediolateral oblique (MLO view). The images are taken, the technologist checks the images for
quality, and the patient is discharged from the mammography department.
The mammogram is an effort to image as much of the breast volume as possible. Because of the
normal breast anatomy, it is impossible to include all of the breast tissue. A mammogram is
usually performed in the standing position. A woman can be imaged seated or in a wheel chair if
necessary, but this may limit evaluation due to limited positioning.
Compression permits fine detail. A good mammogram is not possible without good
compression. Compression holds the breast away from the chest wall, prevents motion, and
spreads the overlapping structures of the breast. Compression also reduces scatter x-rays by
reducing the thickness of the tissue, permits more uniform exposure and reduces the dose
required for proper exposure.
Proper compression thins the breast as much as possible and spreads the breast structures. The
determining factor for compressibility is the elasticity of the skin. Once the skin is taut,
additional pressure only leads to discomfort. Therefore, compression should be applied until the
skin becomes tight or the patient asks that it be stopped.
Mammography should not be painful. The best time for a mammogram is in the first half of the
menstrual cycle for premenopausal women because the breasts are less likely to be edematous
and sore.
Diagnostic Mammography
Diagnostic mammogram is the term used for the problem solving exam. This exam is for the
individual with a sign or symptom that could indicate breast cancer or for the woman who had an
abnormal screening mammogram.
Additional diagnostic imaging includes magnification views, exaggerated CC views, straight
mediolateral or lateromedial views, and rolled CC views among other special views.
Additional imaging is used to gain as much information about the lesion in questions and
surrounding tissue as possible.
In the diagnostic setting, the patient remains in the mammography department while the
radiologist reviews the images obtained, and determines the need for further imaging to include
additional mammographic view and/or possible targeted ultrasound.
The patient typically will be given a verbal report advising the patient of the necessary follow up
before leaving the department. This is followed by a written letter, which is required by law.
Breast Disease
Most breast disease evident by mammography manifests as a mass, distortion, calcification or a
combination.
Additional mammographic views are utilized to assess the location, shape and margins of a mass
and for persistence of architectural distortion. Magnification views are utilized for further
characterization of calcifications (size, shape, density, number and distribution).
Other Modalities
Ultrasound is a useful adjunct in breast imaging. Ultrasound aids in the determination of solid
masses versus cysts. Occasionally, a complex or complicated cyst will require diagnostic
aspiration to prove benignity.
Ultrasound also aids evaluation of shape and margins. In the case of a solid mass, sonography
cannot make a definitive diagnosis of benign or malignant. Because the mammographic and
sonographic appearance of benign and malignant disease can overlap, tissue sampling is
commonly needed for a final diagnosis.
MRI is useful in screening the high risk patient with dense breasts and for the evaluation of
silicone implants. In a patient with newly diagnosed breast cancer, MR1 is also useful to evaluate
extent of disease and assess the contralateral breast for synchronous cancer.
The patient is imaged in the prone position using a dedicated breast coil. Intravenous contrast is
used for MRI screening for breast cancer and evaluating the patient with known breast cancer.
The Male Patient
The normal male breast has a small nipple, small areola, and subcutaneous fat. No fibroglandular
tissue is visible under the nipple on mammography.
Gynecomastia is non-neoplastic enlargement of the male breast. This typically presents as firm
tissue under the nipple, suggesting the presence of actual breast tissue. With true gynecomastia,
the ducts increase in number and may become dilated. "Pseudo-gynecomastia" is enlargement of
the breasts due to fat deposition.
Most cases of gynecomastia are bilateral and symmetric. The diagnosis in these cases is typically
clinical. Asymmetric thickening or pain usually leads to referral for imaging.
Breast cancer can occur in males, although is extremely uncommon, representing less than 1% of
annual breast cancer diagnoses. Most are eccentrically located and occur away from the
subareolar region.
Standard mammographic views can be obtained of a male patient. Ultrasound is of limited value
in the male breast evaluation, except to determine whether a mass is amenable to biopsy by
ultrasound guidance.
Image Guided procedures
Minimally invasive procedures:
■ stereotactic biopsy (x-ray guidance)
■ ultrasound guided biopsy/aspiration
■MRI guided biopsy
■ Wire localization prior to surgical excision
There are several advantages of percutaneous needle biopsy. There is essentially no cosmetic
deformity, minimal mammographic alteration and minimal time for biopsy to be performed and
results to be available. Also, having the diagnosis ahead of time allows the surgeon to potentially
perform one operation. This saves the patient from additional surgeries (and general anesthesia)
as well as saves cost to the health care system as a whole.
Contraindications to percutaneous needle biopsy include but are not limited to inability of the
patient to cooperate for the procedure, inability of the patient to consent to the procedure, allergy
to local anesthetic, and coagulopathies (hematological disorders or drug induced). There may
also be technical limitations, which may not allow for percutaneous biopsy.
BI-RADS Categories
BI-RADS 0: Assessment Incomplete - needs additional imaging evaluation
BI-RADS 1: Negative - routine mammogram in 1 year recommended
BI-RADS 2: Benign - routine mammogram in 1 year recommended
BI-RADS 3: Probably Benign - short interval follow up suggested
BI-RADS 4: Suspicious of Malignancy - biopsy should be considered
BI-RADS 5: Highly Suggestive of Malignancy - appropriate action should be taken