• Understand mammography and how a mammogram is viewed
• Learn new terminology associated with mammography in order to describe breast lesions
• Understand and learn basics about breast ultrasound
• Learn basics about correlation of a lesion found on mammogram and it's corresponding ultrasound image

Breast cancer mortality in the United States is second only to that of lung cancer. For women between the ages of 40-55 years, it is the leading cause of death. In 2005, approximately 40,410 women and 460 men in the U.S. are expected to die from breast cancer. Because of its role in early tumor detection, screening mammography has played a substantial role in reducing the mortality rate by nearly 20% in the last decade.

Note: Click on images for larger views

Risk factors for female breast cancer include:

• Early menarche
• Late age at onset of menopause
• History of breast cancer in mother, sister or aunt
• BRCA1 & BRCA2 genes thought to be responsible for familial cases
• First full term pregnancy after 30 yrs of age
• Nulliparity
• Obesity

The World Health Organization (WHO) identifies breast cancer as:

• Non-invasive type (carcinoma in situ)
• Invasive type)
• Pagets disease of the nipple)

In situ carcinoma is characterized by presence of the tumor within the ducts and lobules without any invasion of the basement membrane. It is further subdivided into ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). Invasive carcinoma denotes invasion of this membrane with extension into the mammary stroma. It may be ductal, medullary, mucinous/colloid, tubular or papillary (brief definitions of each).

Pagets disease involves the nipple and areola and is very rare; accounting for only 1% of all breast cancers, and is often misdiagnosed and treated as dermatitis or bacterial infection Mammary Pagets disease occurs almost exclusively in women and unilateral involvement is more common than bilateral. In situ carcinoma is found in nearly 65% of those cases. Mammography along with punch, wedge or excisional biopsy of the lesional skin of the nipple- areola complex are usually required to make an accurate diagnosis of Pagets disease.

Figure 1 - Breast Anatomy

Each adult female breast consists of nearly 15-20 lobes arranged in a circular fashion. Each lobe is made of several lobules. The ducts draining all the lobes and lobules converge to form lactiferous ducts which merge just beneath the nipple to form a lactiferous sinus. The terminal duct lobar unit is the functional secretory unit at the time of lactation and is lined by a thin layer of myoepithelial cells. Neoplasms can arise in either the epithelium, lobules or stroma.

The soft tissues of the breast are supported by the suspensory ligaments of Cooper. These ligaments run throughout the breast tissue parenchyma from the deep fascia beneath the breast and attach to the dermis of the skin. Since they are not taut, they allow for the natural motion of the breast. Eventually, this results in breast ptosis since these ligaments relax with age and time.

Mammography is the most effective method for early detection of breast cancer. However; in younger patients due to increased density of the breast tissue it may not be very useful in detection of disease.

Mammography uses low dose ionizing radiation along with high contrast, high resolution single emulsion film to demonstrate breast parenchyma and very tiny microcalcifications (which have been shown to be markers for early-stage breast cancer) that may be present within it. Ultrasound, MRI and nuclear medicine have adjuvant roles.

Positioning for Mammography:

The breast can be imaged from several angles. The Mediolateral Oblique (MLO) view is the more common view followed by the Cranio-Caudal (CC) view. Additional views can be obtained to clarify a suspected abnormality detected during screening mammography; such as magnification views, lateromedial view(LM), spot compression views, exaggerated CC views and more.

Figure 2

Skin markers may be used to identify skin abnormalities or the nipple on a mammogram. Breast compression is necessary to flatten the breast and allow maximum tissue to be imaged. It also immobilizes the breast and reduces motion blur and helps to lower the X-ray dose and X-ray scatter. It may result in some discomfort to the patient but the benefits of compression far outweigh everything else.

Viewing The Mammogram

The detection of breast cancer involves viewing of tissues thought to be normal. It involves careful scrutiny of normal breast parenchyma and detection of any disruption in it. An initial 'bird's eye' evaluation of both breast images needs to be performed to evaluate size, shape, symmetry and overall density of breast tissue on the mammogram.

This is followed by a close-up in-depth scrutiny of each individual image to look for any disruption of normal breast parenchyma, presence of masses, calcifications or areas of architectural distortion. Once an area of the breast is identified as being a solitary geographic abnormality then one can proceed to the second step; which involves determination of whether the abnormality is a normal variation or benign process.

A solitary geographic abnormality may be any of the following:

1. Mass: defined as a dense space occupying lesion seen on two different projections with convex outer borders. It is usually denser in the center than the periphery. Its margins may be sharp & circumscribed (benign cyst) or spiculated, lobulated/undulating, indistinct or obscured suggestive of malignancy. Circumscribed margins are sharply demarcated with an abrupt transition between the lesion and surrounding tissue, with nothing to suggest infiltration and are a reassuring characteristic. Spiculated margins on the other hand are suggestive of surrounding parenchymal infiltration. Also shape, size and density of the mass should also be analyzed. For example; schirrhous cancers tend to have a density greater than normal breast tissue while low density masses are usually suggestive of fat containing, usually benign lesions like lipomas, oil cysts, hamartomas and galactocoeles.
   
   

   Breast Mass - Shapes	Breast Mass - Margins
   Figure 3

   
   
   
2. Architectural Distortion: Defined as a disruption of the normal random pattern of the fine linear or curvi-linear radio-opaque structures (architecture) seen in the breast. It is not associated with the presence of a mass and can often manifest itself as spiculations radiating towards a point from the nipple or focal retraction along an interface of fibroglandular tissue. It may be associated with malignancy more commonly, but is often seen post surgery or post radiation therapy.
3. Focal Assymmetric Density: It is an asymmetry of fibroglandular tissue density with a similar shape seen on two views of the mammogram but lacking the convex outer borders and conspicuity of a true breast mass. It may have fat traversing through it.
4. Microcalcifications: These result from deposition of calcium salts in breast tissue. The majority are composed of calcium phosphates in the form of hydroxyapatite. Their distribution is important as is their characterization, as they may be in clusters or segmental along a major duct system; or just diffusely scattered in the breast. Coarse or Popcorn microcalcifications , > 1mm are usually benign and may be associated with degenerating fibroadenomas. Round microcalcifications are small, < 1mm and are located in the acini of the breast lobules. Pleomorphic calcs are < 0.5mm and vary in shape and size and along with the linear and punctuate types and are often associated with malignant lesions in the breast. Almost all varieties of ductal carcinoma in situ (DCIS) cases display grouped microcalcifications. They may be pleomorphic , linear , branching or segmental. High grade DCIS (comedo type) presents as pleomorphic linear or branching microcalcifications. Low grade DCIS( cribriform or micropappillary type) presents as granular or amorphous microcalcifications with less pleomorphism.
5. Density: It is described in the American College of Radiology-Breast Imaging Reporting & Data System (ACR-BIRADS) lexicon as a focus of fibroglandular tissue seen only on one view.
6. Skin Lesions: Typically these may be visualized as densities surrounded by a 'black halo' due to a thin rim of air trapped around it during compression for mammography. Tangential views on mammography can help make a definitive diagnosis of skin lesions.

Originally ultrasound was used to distinguish simple cysts from solid masses. However, with improvement in the equipment quality and scanning techniques today the applications and uses of breast ultrasound have significantly expanded. Today ultrasound plays an important role in guiding interventional procedures and more recently screening ultrasound is being advocated for patients with dense breasts, where there is a greater chance of lesions being obscured on conventional mammography.

On ultrasound, a normal breast is divided into six zones from superficial to deep. The skin is most superficial and approximately 2mm in thickness, followed by subcutaneous fat, pre-mammary fascia, mammary zone, retromammary fascia and pectoralis muscle. Most of the breast cancers detected by ultrasound are located in the mammary zone. In a 1995 landmark study, Stavros et al established certain ultrasound criteria to characterize breast masses. It was suggested that ultrasound can be used to classify some solid masses as benign , allowing for follow-up with imaging rather than biopsy. They proposed to classify breast nodules as Benign, Indeterminate or Malignant. Of the 424 lesions that Stavros et al classified as benign using ultrasound, only 2 were malignant at biopsy; resulting in a negative predictive value of 99.5%. Biopsy was recommended for nodules classified as Intermediate or Malignant on ultrasound and follow up for those classified as Benign.

Characteristics of a Benign Nodule are :

• Ellipsoid shape or wider than taller orientation with a thin echogenic capsule and a width to AP dimension ratio of 1.4 or more.
• Uniform echogenicity or intense homogenous hyperechogenicity
• 2-3 gentle lobulations

Characteristics of a Malignant Nodule are:

• Hypoechogenicity
• Spiculated contours/Angular margins
• Taller than wider orientation
• Posterior acoustic shadowing
• Duct extension, branching pattern
• Presence of suspicious microcalcifications

Although the appearance of breast carcinoma can vary, some patterns are typical. Mucin containing tumors are often well circumscribed and may be either iso or hypoechoic on ultrasound; relative to the subcutaneous fat. Less than 2% of mucinous carcinomas can become invasive. Tubular carcinomas can be hypoechoic, without circumscribed margins or shadowing. Invasive ductal carcinomas may present as irregular masses with spiculated margins, shadowing and adjacent architectural distortion. Malignant microcalcifications are usually present.

Sonographic detection of breast microcalcifications:
When detected , breast microcalcifications are seen on ultrasound as distinct echogenic reflectors contrasting with a background hypoechoic or mass or duct that increases the conspicuity of the calcifications. Ultrasound is most successful at showing large areas of highly suspicious microcalcifications; although much is dependent on their depth, operator skill and equipment in use. Small faint clusters seen on mammography are usually not seen on ultrasound.

• Linear array transducer > 7Mhz to be used
• Set focal zone at depth of the lesion
• Gain settings to be adjusted to allow simple
cysts to be distinguished from solid masses and fat to be medium or light gray.
• Breast lesions to be viewed from two perpendicular projections
• Maximum dimensions of the mass to be included
• Label images as Right or Left and specify location (by quadrant, clock position, distance from nipple or shown on body pattern)
• Indicate probe orientation
• Permanent identification to include Patient’s first and last name, ID number, Age/Date of Birth, Facility location, date and sonographer initials.

1. Ribs: In cross-section the cartilaginous portion of a rib may appear like a suspicious breast mass
2. Nipple: An inverted nipple can mimic a suspicious hypoechoic mass with posterior attenuation because of the presence of dense connective tissue and smooth muscle bundles.
3. Fat Lobules: In cross-section, fat lobules can be mistaken for an isoechoic mass. Its normal appearance can be revealed by rotating the transducer until it is stretched out.
4. Acoustic shadowing without a mass may be just incidentally seen in a normal breast. A thin column of shadowing may be due to a 'Cooper's ligament' – which is a normal suspensory fibrous strand of the breast parenchyma. Usually, shadowing from Cooper’s ligaments is faint and narrow but sometimes can be wide and hypoechoic; enough to simulate a tumor. It often resolves with mild transducer pressure or change in the angle of insonation.
5. Post surgical scars can cause shadowing without an associated mass.
6. Inappropriately high gain settings on the ultrasound equipment may result in spurious echoes being displayed in a cyst; resulting in a false positive diagnosis of a complex cyst or mass. The gray scale gain should be set so that fluid in a cyst appears black and fat lobules appear dark or light gray on a cyst phantom.
7. Focal Zones should be set to match the depth of the lesion being imaged.
8. Air introduced during a biopsy can appear as thin echogenic lines in the needle tract, often mimicking the appearance of a needle or foreign body remaining inside.

Recent advances made in computer technology, probe technology and image display techniques today have resulted in the rapid evolution of modern breast ultrasound. Some ultrasound scanners today have several new tools to enhance image quality such as Spatial Compounding, which acquires multiple coplanar images and combines them into a single real time image. Spatial Compounding reduces artifactual noise and enhances border definition. This is very helpful when differentiating fluid filled versus solid areas as well as in defining edge definition in masses.

Speckle Reduction Imaging is an adaptive real time software algorithm, which reduces the speckle artifact inherent to ultrasound imaging. Reducing the speckle artifact results in an image that more closely approximates tissue resulting in improved contrast resolution and increased visual conspicuity. Speckle reduction technology can be very helpful in separating small structures from the noise inherent in ultrasound signal processing.

Improvements in probe technology have led to the advent of new lightweight Matrix Array Transducers operating at high frequencies, which along with the use of Harmonic frequencies have resulted in remarkable improvements in overall image quality.

Three-dimensional ultrasound of the breast is also rapidly gaining popularity since it can demonstrate a lesion and its margins and topography in multiple planes including the coronal plane. Some modern ultrasound scanners have small parts transducers with frequency ranges as high as 16 MHz. and are capable of producing high-resolution 2D gray scale images as well as 3D and 4D rendered images with ease.