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Mammography

 

 

MAMMOGRAPHY
Dr. Edward Jankhe
Department of Radiology
Providence Saint Joseph Medical Center, Burbank, CA

TABLE OF CONTENTS

1. Mammography: The Technique
2. Guidelines
3. Definitions of Mammographic Lesions
4. Benign Mammographic Lesions
5. Suspicious Mammographic Lesions
6. Exposure Risks
LORAD Mammography System Excluding skin cancer and in situ carcinomas, breast cancer is the most common cancer occurring in females, with a lifetime incidence of about 12.6% ( 1 in 8). It is also the second most common cause of cancer death in females. The American Cancer Society estimates that in 1997 there will be 181,600 new cases of breast cancer in females, and an estimated 43,900 women will die from breast cancer. Breast cancer develops over a period of years, and controlled medical studies have show that if it is detected in a localized stage, without spread to regional lymph nodes, the 5 year survival is about 97%. However, when the cancer has spread to axillary lymph nodes the 5 year survival decreases to about 76%, while the 5 year survival decreases further to about 20% with distant metastases to the lung, bone marrow, liver or brain. This improved survival with early detection is the rational for breast imaging and screening mammography in particular. Breast imaging and mammography also play a role in defining the extent and nature of palpable abnormalities, or the presence of additional occult disease in cases of clinically evident abnormality and prior to therapeutic intervention.

MAMMOGRAPHY: THE TECHNIQUE

Mammography refers to breast imaging with the use of x-rays. The x-ray images are produced by the attenuation (absorption) and scattering of the x-ray beam by the various breast tissues before the beam reaches and exposes the film. The first reported use of X-rays to demonstrate breast cancer was in 1913, by Dr. Albert Solomon who obtained radiographs of gross anatomic mastectomy specimens. Over the subsequent 70+ years the technique has been developed and refined through the use of dedicated units, compression, molybdenum targets, standardized techniques, moveable grids, automatic exposure control, high resolution films, rare earth screens, automatic film processing and ever greater attention to quality control. Dedicated mammographic units are currently sold by multiple vendors with generally minor differences in technical specifications.

Currently mammography is performed with a dedicated mammography unit, to optimize radiographic exposure and breast compression; and with rigorously controlled film processing and development to optimize image quality. Because the x-ray images depend on differential attenuation of the x-ray beam by the different breast tissues, if may be difficult to separate normal functioning breast tissue from a benign or malignant mass. As a consequence mammography is less sensitive in dense breasts than in fatty, involution breasts.

Both screening and diagnostic mammograms routinely start with the standard mediolateral oblique and craniocaudal projections. For further evaluation of suspected abnormalities supplemental views including exaggerated craniocaulal, spot compression, magnification, vertical lateral, tangential, and push-back views may be obtained.

The spot compression view, with or without magnification, is used to separate a suspected density from adjacent parenchyma and better define its margins. Spot compression magnification views also better define the presence and morphology of various breast calcifications and masses.

Tangential views are useful to define the relationship of a parenchymal density or calcifications to the skin.

Vertical lateral views better define the anatomic location of lesions within the breast as well as demonstrate the presence of Milk-of -calcium ( calcium precipitate) within small cysts.

Push-back (Ekland) views allow improved imaging of breast tissue anterior to breast prostheses.

Comparison to old studies is also useful for evaluation of stability or interval change.

MAMMOGRAPHY: GUIDELINES

Based on review and discussions of the available scientific evidence, The American Cancer Society recently changes it’s recommended guidelines for screening mammography to include yearly screening for all women 40 years of age and older. Previously the recommendation had been for screening mammography every 1-2 years.

The current guidelines are:

American Cancer Society Recommendations for Breast Cancer Detection in Asymptomatic Women (March 23, 1997)
20-40 Years of Age
  • Beast self examination monthly
  • Breast clinical examination by a healthcare professional every 3 years,
  • No recommended Mammography
40 and Older
  • Breast self examination monthly,
  • Breast clinical examination by a healthcare professional very 3 years,
  • Mammography every year
Cessation of annual screening is not considered to be age-dependent, but a function of co-morbidity; and no termination age was specified.

DEFINITION OF MAMMOGRAPHIC LESIONS

The sensitivity of mammography is initially determined by the relative background composition of the breast parenchyma. The denser the breast the less sensitive it is to the detection of small masses, although small calcifications can generally still be detected. The mammograms are initially evaluated for the presence of masses, architectural distortion, asymmetric parenchyma, calcifications and skin changes. These mammographic findings are then further characterized and compared to old studies, if available.

Mammographicaly a mass is defined as a space occupying lesion seen in two different projections, with density defined as a collection seen in only one view. A mass is then further characterized by it’s shape, margins, density, size, orientation and presence of associated calcifications.

  • Shape is a generally nonspecific characteristic, both benign and malignant masses tend to develop in one spot and grow circumferentially. An irregular shape is more concerning as its suggests indistinct or irregular margins. Some skins lesions, warts and seborreic keratoses, have typical appearances due to the variegated surfaces and occasionally radiolucent/air halo. Some intramammary nodes have a typical reniform configuration with a fatty notch.
  • Margin or contour analysis characterizes the transition zone from mass to surrounding parenchyma or fatty tissue. The significance arises from the tendency of invasive carcinoma to infiltrate adjacent tissue and have indistinct, microlobulated or frankly spiculated margins.
  • Well circumscribed or sharply marginated masses, either with or without a radiolucent halo, are probably benign. If all margins remain sharply circumscribed on magnification views , and there is no associated suspicious calcification, 98% to 99% will be benign with a differential of fibroadenoma, cyst or intramammary lumph node. When initially found ultrasound to exclude a cyst is a very useful adjuvant study. If the lesion is solid on ultrasound, serial six month mammograms for two years would be suggested, because of the low, 1-2%, incidence of malignancy. An alternative to serial imaging would be FNA or core needle biopsy.
  • Circumscribed masses with irregular or microlobulated margins on magnification views should be considered suspicious and biopsy suggested.

mammo1.jpg (31676 bytes)

Similarly if the margins remain indistinct or ill-defined on additional special views the lesion must be considered suspicious and biopsy considered.

  • Masses with spiculated margins are suggestive of malignancy.

mammo2.jpg (30613 bytes)

With cancer, the spicules represent finger-like projections of the malignant cells. Other spiculated densities may represent radial scar/sclerosising adenosis but are still suspicious and can be associated with tubular carcinoma. A spiculated density may also be secondary to a post operative scar, although the clinical history should provide the clue and subsequent serial follow up should demonstrate maturation and involution or at least stability of the scar.

  • Density describes the relative attenuation of a breast lesion compared to the normal fibroglandular tissue of the breast. Cancer is frequently, but not always higher in density than surrounding parenchyma, and can be isodense or rarely lower in density. Fat containing/radiolucent masses most frequently represent oil cysts, lipoma, galactocele, hamartoma or fibrolipoma, and are considered benign unless other characteristics are suspicious.
  • Calcifications can occur in the breast from many causes and be associated with both benign and malignant conditions. Many benign calcifications have a typical appearance but some may be indeterminate or simulate malignant calcifications. Suspicious calcifications occur in about one-third of breast cancers, and may develop before the invasive phase. Some benign type calcifications have a typical appearance, while others are more nonspecific but are usually larger, and coarser than the suspicious calcifications. The pattern of distribution may also be helpful in evaluating the calcifications, with clustered, segmental and fine linear or branching patterns being more suspicious.

MAMMOGRAPHIC LESIONS: TYPICALLY BENIGN

  • Skin calcifications are typically small round to oval with lucent centers.
  • Vascular calcification is similar to elsewhere in the body and forms contiguous or interrupted dense paired tubular lines.
  • Coarse or popcorn like calcification can be seen in an involuting fibroadenoma.
  • The large rod shaped calcification of secratory disease/plasma cell mastitis are usually over 1mm in diameter, may have lucent centers and occasionally branch.
  • Small, dense rounded calcifications are usually considered benign and related to involution.
  • Milk of calcium is benign and represents calcium precipitate in small cysts.
  • Eggshell calcifications are benign
  • Small amorphous, indistinct, hazy rounded and flake like calcifications may be associated with both benign and malignant process and are of intermediate concern.

MAMMOGRAPHIC LESIONS: HIGH PROBABILITY OF MALIGNANCY

  • Pleomorphic or heterogeneous (granular) fine linear and/or branching calcifications.

EXPOSURE RISKS FOR MAMMOGRAPHIC STUDIES

UNDER CONSTRUCTION

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