Mammography: A Brief Introduction

Mammography has revolutionised the way Breast Cancer is diagnosed, allowing earlier detection and treatment.

In this article, we will be covering the breadth and depth of this technology.
You will learn what a mammogram is and how safe it is.
We’ll also be covering when screening should be done and how frequently, before going into details of radiological findings.

What is a Mammogram? 

Mammogram is a radiological tool that is used in imaging the breast tissue. In simple terms it is an X-ray of the breast. 

Mammograms do not help in preventing breast cancer but it helps in its early diagnosis, and plays an important role in breast cancer related deaths. 

Screening mammography permits diagnosis at an early stage of the disease and is therefore attributable to the decline in mortality.
(Preinvasive breast cancer (Ductal carcinoma in situ[DCIS]) now accounts for 25-30% of  newly diagnosed, mammographically detected breast cancers.)

How does a Mammogram work? 

Mammogram is a type of X-ray device that focuses on imaging of the breast. A mammography unit is designed to improve the image quality of the breast tissue without an increase in the radiation dose. 

The unit consists of a paddle that compresses the breasts and takes images at various angles.

Standard Mammography views

Two views are the basic components of a standard mammogram- craniocaudal(cc) and mediolateral oblique(mlo). This allows for maximum visualisation of the breast while obtaining a 3D understanding of visualised structures. 

In craniocaudal view the beam enters the cranial(head) end of the breast and exits the caudal(towards the feet) end. A correct cc view shows the pectoralis muscle at the posterior end of the breast which means that the breast is positioned as far forward as possible, but this is not always achievable. 

An optimal cc view requires the nipple, the pectoralis and the lateral portion of the breast to be included. 

Mediolateral oblique (mlo) view is the most important as it includes maximum breast tissue. The amount of pectoralis muscle visible in the image determines the amount of breast tissue included, this helps in improving the sensitivity of the breast. 

The angle used in mlo is 45 degrees, although the angle may be adjusted between 40-60 degrees  to maximize breast tissue visualisation. 

Is Mammography safe? 

The radiation dose used in mammograms is extremely low and the risk of harm from this radiation is extremely low.

The total dose received during a screening mammogram is around 0.4 mSv.
The average amount of background radiation exposure in an individual in a year is around 3 mSv.
The exposure from a single mammogram is about equal to the background radiation dose received over a period of 7 weeks. 

It must be noted that compression of the breasts during mammogram does not increase the risk of spread of the disease. 

When are Mammograms done?

When women present with a new mass, diagnostic mammograms should be a part of the initial workup, even if the patient is young.

Screening recommendations for mammogram as per the American Cancer Society

Breast cancer screening recommendations are based on age and risk factors.

Who are high risk patients?

  • Those with personal history of breast, ovarian,tubal or peritoneal cancer
  • Family history of breast, ovarian,tubal or peritoneal cancer
  • Ancestry associated with BRCA1 or 2 mutations
  • Known carrier of a pathogenic mutation associated with breast cancer(eg.BRCA1,2, PTEN, p53)
  • Previous breast biopsy indicating high risk lesion(eg. Atypical hyperplasia)
  • Radiotherapy to the chest between 10-30 years of age.

Woman with none of these risk factors are considered as average risk.

Average risk have a less than 15% lifetime chance of developing breast cancer. Majority of women fall under average risk category. In these women age is the most important  factor in deciding when to be screened, since breast cancer incidence increases with rising age.

  • Women aged 40-49 with average risk– Women aged 40-44 years should have the choice to start annual breast screening mammograms if they wish so.

Women aged 45-49 years should get an annual screening mammogram.

  • Women aged 50-74 with average risk– Women aged 50-54 years should get mammograms every year.
  • Women aged 55 years and above should get a chance to switch between, 2 years or have the choice to continue yearly screening.
  • Women 75 years and above- Screening should continue as long as the woman is in good health and has a life expectancy of 10 years or longer.

Women at higher than average risk– Women who are at high risk for breast cancer should get an MRI and a mammogram every year.

Screening is of greatest value for those patients who are likely to develop breast cancer and for whom early intervention would help in reducing mortality.

BIRADS categorisation 

After a patient gets her mammogram done the radiologist gives the report based on BIRADS criteria. 

BI-RADS assessment categories are used which indicate the relative likelihood of a normal, benign or malignant diagnosis and the follow up steps that needs to be taken. 

BI-RADS (American College of Radiology(ACR) (Breast Imaging Reporting and Data System)  categories-

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BI-RADS Classification

If a mammogram is assigned category 0 additional evaluation is required such as additional views, ultrasound and rarely MRI.

BI-RADS category of 4c or 5 suggests that a malignant diagnosis is strongly suspected and that further evaluation(and probably a rebiopsy) is needed if the biopsy is initially interpreted as benign.

What do we look for in a Mammogram? 

Before looking into the abnormal findings on mammogram it is important to know in brief about a normal mammogram.

Normal mammogram

In the above image of a normal mammogram, there is adequate exposure of the pectoralis muscle which appears homogeneously opaque, glandular and connective tissue appears white against a dark background.
Chassaignac’s bursa is the adipose tissue that outlines the retromammary space posteriorly.
Crests of Duret accommodate the cooper’s ligaments.

In a mammogram the background will be black and the breast will remain grey and white.

Dense tissue such as glands and connective tissue show up as white.

Some patients have more dense tissue in the breast which can make it harder to detect a tumour since tumour is also made up of dense tissue. 

It must be noted that no two mammograms will look the same as everyone’s breasts are different.

What exactly does dense breasts mean?

It means that the breast tissue has higher amounts of fibrous and glandular tissue with less fat. If a patient’s breasts are firm, it does not mean that she has dense breasts. Dense breasts can only be detected on mammogram.

Dense breasts are common and not abnormal.

Breast density is divided into four main grades-

  • Grade 1– Almost the entire breast is fatty
  • Grade 2-There are scattered areas of fibroglandular density
  • Grade 3-Most of the breasts are made up of dense fibrous and glandular tissue, and appear ‘heterogeneously dense’.
  • Grade 4– Extremely dense breasts which lowers the sensitivity of the mammogram.
Grades of dense breast tissue, Grade 1 to 4 from left to right.

Majority of the breast cancers are associated with abnormal mammographic findings. When a patient comes for a screening or diagnostic mammogram, the radiologist looks for evidence of benign or malignant breast conditions that may require further evaluation

Benign breast findings on a mammogram-

  • Simple cysts– Fluid containing sac, that are benign. They may appear malignant on mammogram, but are better appreciated on ultrasound.
  • Fibroadenomas– Benign condition that may appear as a malignancy on mammogram. Fibroadenomas appear as discrete well circumscribed mass on mammogram.
    In older patients typical coarse coarse popcorn calcifications maybe present. Calcification may present as crushed stone like microcalcification which makes it difficult to differentiate from malignancy.

    Confirmed by tissue diagnosis.
Popcorn calcification
  • Fibrotic changes– as a woman ages her breast may undergo fibrotic changes. Focal fibrotic changes in the breast may mimic a malignancy on mammogram. Needle biopsy may be necessary to confirm the diagnosis.
Fibrotic changes on mammogram

Mammographic features of breast cancer

Mammographic findings are divided into two general categories- soft tissue masses and suspicious microcalcifications.

Soft tissue mass/architectural distortion– most specific mammographic feature of malignancy is spiculated soft tissue mass, 90 % of these lesions represent invasive cancer.

Image result for mammogram spiculations
Spiculated soft tissue mass

Approximately one third of non calcified cancers appear as spiculated masses, 25% as irregularly outlined masses, 25% as less specific round, oval or lobulated masses; less than 10 percent as well defined round, oval or lobulated masses and 5 % as architectural distortion of dense tissue without an obvious mass. 

Solid circumscribed masses that are oval have a less than 2% likelihood of malignancy.

Calcifications– calcifications are the result of cell secretions, cell debris, inflammation and trauma.

Image result for microcalcifications on mammogram
Microcalcification

Microcalcifications– Grouped microcalcifications are calcium particles of size 0.1-1 mm in diameter and are numbering more than 4-5 per cubic centimetre. They are seen in approximately 60% of cancers detected mammographically.

These microcalcifications represent intraductal calcifications of necrotic tumour or calcifications within mucin secreting tumours such as the cribriform or micropapillary subtype.

Linear branching microcalcifications are associated with comedo subtype and are more associated with malignancy than coarse heterogeneous microcalcifications.

Calcifications that are not suspicious of malignancy include vascular and skin calcifications, rim calcifications, large and coarse calcifications.

Even though microcalcifications are associated with DCIS, there is no mammographic correlate of basement membrane invasion.

20% of invasive carcinomas diagnosed by mammography present only as microcalcifications.

Grouped coarse heterogeneous calcifications have less than 15% likelihood of malignancy.

Image result for coarse calcifications on mammogram
Grouped coarse calcification

Amorphous calcification would have a likelihood of 20%.

Image result for amorphous calcifications on mammogram
Amorphous calcification

Grouped coarse and amorphous both come under BI-RADS category 4b.

Grouped round and punctate calcification have a probability of malignancy under 2% and come under BI-RADS category 3- probably benign.

Image result for punctate calcifications on mammogram
Punctate calcifications

Mammographic assessment of disease extent

Mammographic assessment of the DCIS and invasive disease starts from mammography, biopsy and post excision mammography.

Preop mammography can help in assessing the extent of the disease and may identify multifocal and multicentric disease that could preclude breast conservation and may signal a difficulty in achieving a negative surgical margin.

Multifocal disease

Defined as involvement of several areas within a breast quadrant, probably representing disease along an entire duct.

Multicentric breast disease

The presence of two or more foci of breast cancer within different quadrants of the same breast. 

Image result for multifocal disease breast
Image result for multifocal mammography
Multifocal breast disease
Image result for multifocal mammography
Multicentric breast cancer

The extent of mammographic nonlinear calcification frequently underestimates the pathological disease the discrepancy being less than 2 cm in 80-85% of cases.

Extensive Intraductal Component(EIC)- The combination of a mass and associated calcifications indicates the presence of an EIC. It is pathologically defined as DCIS found adjacent to invasive carcinoma and accounts for more than 25% of the disease. This finding can be a predictor for more widespread residual tumour following gross excision of the lesion.

When margins are positive or when microcalcifications are not clearly documented on the specimen radiograph postoperative mammograms to look for residual calcifications should be performed.

If a reexcision is planned based on microcalcifications, care should be taken that the calcifications are associated with malignancy and not benign tissue.

A significant limitation of mammography is the obscuring of the borders of the primary tumour by dense breast tissue. If the clinical extent of the disease is greater than what can be obtained from mammography MRI maybe considered. MRI may be necessary to look for posterior extent of tumour and to assess pectoralis muscle invasion.

Significance of intramammary lymph nodes

Intramammary lymph nodes are detected in 1 to 28 percent of women with breast cancer. Benign nodes can be differentiated from metastatic lymph nodes based on mammographic or sonographic appearance and can be confirmed by histopathologic study. The presence of intramammary lymph nodes signifies a worse prognosis. Isolated intramammary lymph nodes are considered stage II disease even if axillary lymph nodes are uninvolved.

Image result for intramammary lymph node mammogram
Intramammary lymph node

It must be noted that although mammograms are the breast cancer screening tool available today for breast cancer, not all breast cancers are detected on mammograms. These come under false negatives. There may be abnormal findings but no cancer present, this is called a false positive result.

Efforts are being made to improve conventional mammography techniques to reduce the rates of false positive and false negative results.New techniques such as digital mammography, 3D-mammography(or tomosynthesis mammogram) help in reducing the number of false positives and false negatives.

These techniques will be discussed in a separate article.
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