Breast Imaging

Screening Mammography for Breast Cancer Dr. B. Lohani, Dept. of Radiology & Imaging TU Teaching Hospital, Maharajgunj.

Introduction: Breast cancer is the most frequently diagnosed cancer & is the second leading cause of potentially avoidable cancer mortality among women. Breast cancer is largely found in older women. The cancer survival is influenced by the size of the lesion & the status of the axillary lymph nodes. Breast screening is a method of detecting cancer at a very early stage. The key to curing breast cancer is early detection & prompt treatment. A physical examination, mammography & breast self examination make up the conventional early detection approach. A mammogram is a special picture of breast. It can detect small changes in breast tissue which may indicate cancers which are too small to be felt either by self examination or by a doctor. Outcome of Screening: Population based mammography screening aims to reduce morbidity & mortality from breast cancer by early detection & treatment of occult

malignancies. As the cancer survival depends on the stage of the disease small tumors with negative axillary nodes are detected more often in mammography than with physical examination. It was found that annual/biennial screening has led to significant reduction in mortality from cancer (30% in 50 – 69 yrs age group). The sensitivity of mammography is 75 – 95% with specificity of 90 – 95% for detection of cancer with positive predictive value (PPV) of 20% for less than 50 yrs & 60 – 80% for 50 – 69 yrs. Detection of cancer at early stage also has the benefit of less disfiguring & less toxic treatments as small tumors are amenable to breast conserving surgery which is very important form patients' perspective. Screening Guidelines: The screening guidelines are provided by the American Cancer Society, American College of Radiology & American College of Obstetricians & Gynecologists. The recommendations include screening mammography every 1 – 2 year for 40 – 49 yrs age &

annually after the age of 50 yrs. High risk group should seek expert advice of physician for regular screening before the age of 40. It is stated that the outcome of well established screening program should detect more than 50% cancer at the minimum (non invasive or invasive with less than 1 cm size with no nodes) & more than 80% of the detected cancers should be node negative at surgery/ pathology.

The false negative mammograms are due to non inclusion of palpable mass in the film, dense breast, technical inadequacy etc.

Radiation Risk: An increased susceptibility to breast cancer has been documented among women exposed to high doses of radiation (1 to 20 Gy). The

radiation dose for a standard two-view examination of both breasts is approximately 4.5 mGy. A risk–benefit calculation in the UK has established that the benefits of screening far outweigh the risk of inducing a cancer, with the ratio of lives saved to lives lost calculated as approximately 100:1.The latest follow-up data from the Japanese atomic bomb survivors have shown progressively decreasing radiation risk with increased age at exposure. Women who were exposed in their youth and teens suffered the highest increase in risk. No increased risk was demonstrable for women aged 40 or older at exposure. Technical Consideration: Because both high contrast and high spatial resolution are needed standard radiographic equipment cannot be utilized for this examination. Mammography is performed in dedicated mammography units which provide greater contrast between soft tissue structures. All mammographic units are equipped with compression paddles that squeeze the breast against the film holder. Compression has the advantages of a) spreading of overlapping structure (differentiation of the masses vs. summation shadows), b) immobilization (prevents image blurring), c) providing uniform thickness of breast & d) reduced radiation dose. Though mammography can be performed while standing or sitting, standing is preferred as more breast tissue can be included for examination. Screening is accomplished with standard two views i.e. MLO (medio-lateral oblique) and CC (craniocaudal) views.

MLO view: The breast is compressed in supero-medial direction. This is the most useful view as greatest amount of breast tissue is along with the pectoralis major muscle and inframammary fold.

CC view: For craniocaudal view breast is compressed in horizontal direction. The pectoralis major muscle is visible in about 30% of patients. Full field digital mammography has advantage of higher contrast resolution with increased conspicuity of the lesions.

Interpretation: For correct interpretation detailed clinical information relevant to breast health and cancer risk should be provided along with patient's history and any previous surgical biopsies or HRT. The mammographic findings should be correlated with physical examination. For interpretation, CC and MLO mammograms should each be viewed together in a mirror-image configuration which allows the radiologist to scan the breasts for symmetry A magnifying lens should be used to examine each film thoroughly. All visible parenchyma should be scanned systematically with magnification. This will allow visualization of tiny microcalcifications and will ensure that the radiologist has examined all parts of the breast in detail.

Analyzing the mammogram: 1) Normal mammogram:

MLO View

CC View

2) Benign lesion: Mammographic features of typical benign lesion include a well defined circumscribed mass with convex borders with increasing density toward the center. The “halo sign,” which is a partial or complete radiolucent ring surrounding a mass suggest benignity. A benign lesion has normal

surrounding breast parenchyma without distortion of normal breast architecture.

Benign Lesion on MLO View

Benign Lesion on CC View

3) Indeterminate mammogram: Further evaluation should be done with additional mammographic views or ultrasonography. Spot compression and magnification views in mammogram helps in further characterization of the lesion providing finer detail and accurate assessment of morphology of microcalcifications and the border of masses.

Spot Compression view for Calcification 4) Breast Cancer: Clustered pleomorphic microcalcifications with or without an associated soft tissue mass is the primary mammographic sign of breast cancer which is seen in more than 50% of all mammographically discovered cancers. About 1/3rd non palpable cancers manifest by calcifications without associated mass. When breast cancer presents as mass it classically appears as a spiculated mass on mammogram (<20% on non palpable cancers). Most spiculated masses are infiltrating ductal carcinoma. The cancer may also present as a round mass with indistinct or ill defined microlobulated borders, increasing density towards the center or distortion of surrounding parenchyma.

Malignant lesion Rt breast on MLO view

Malignant lesion Rt breast on CC view

Computer Aided Detection (CAD): It is a computer software system designed to aid the film reader by placing prompts over areas of concern which reduces observational oversight. It is highly sensitive for detecting cancers on screening mammograms. It prompts around 90% of all cancer, 86-88% of all masses and 98% of microcalcifications. However there is no concensus in the literature as to whether CAD improves film reader performance.

Conclusion: Breast cancer represents a significant health problem. Early detection with screening mammography is the only proved way to lower mortality. The challenge for the radiologist is to maintain the highest standards of quality in performance and interpretation of imaging studies and to encourage all women to take regular advantage of these life saving techniques.