Annual Mammograms vs. Annual Ultrasounds

Though mammograms can miss tumors, they offer more information

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A mammogram and breast ultrasound are necessary imaging tests when assessing for the presence of breast cancer. Although a mammogram is the gold standard for breast cancer detection, an ultrasound can identify specific changes in the breast. Since each test complements the other, healthcare providers may use both mammograms and ultrasounds for breast cancer screening and diagnosis.

This article will review the differences between breast ultrasounds and mammograms.

Limitations Ultrasound in Breast Cancer Screening
Verywell / JR Bee

Key Differences

The primary differences between breast ultrasounds and mammograms are their roles in the screening process. While each test is important in identifying possible cancer, their purposes are different.

Purpose of Imaging

A mammogram is an X-ray of the breasts. Mammograms are the most effective breast cancer screening test. They can take multiple pictures of the breast and identify calcifications (calcium deposits within breast tissue). In addition, mammograms are important for diagnosing and following up after breast cancer.

A breast ultrasound, however, is generally used for diagnostic reasons. For example, an ultrasound is most helpful when evaluating dense breasts or a suspicious lump found on a mammogram. A breast ultrasound is good at distinguishing a benign fluid-filled cyst from a solid mass. Furthermore, an ultrasound can help define a mass found by touch, even if it does not appear on a mammogram.

Imaging Modality

A significant difference between a mammogram and ultrasound is how they work. Mammograms use low-dose radiation to x-ray the breasts, while ultrasounds use sound waves, as follows:

  • Radiation: Although you will be exposed to small amounts of radiation during a mammogram, the benefits usually outweigh the risks. However, if you're pregnant, radiation from a mammogram can harm the fetus.
  • Sound waves: The sound waves generated by an ultrasound create an echo that produces the ultrasound image. No radiation is emitted during a breast ultrasound.

A 2016 study in the Annals of Internal Medicine found that although 125 women out of 100,000 may experience radiation-induced breast cancer through mammograms, 968 deaths could be prevented by early detection with a mammogram.

Image Quality

Image quality can differ as follows:

  • Mammograms: If a screening mammogram identifies a suspicious area in the breast, you will likely need a diagnostic mammogram. A diagnostic mammogram takes more pictures than a routine screening mammogram and focuses on the affected area.
  • Ultrasounds: A breast ultrasound is unable to identify microcalcifications. Although calcifications aren't always indicative of breast cancer, many early breast cancers are suspected due to their presence.

Recent studies suggest that women who have dense breasts could benefit from a mammogram plus fast breast magnetic resonance imaging (fast breast MRI). The combination of both tests may produce fewer false positives than mammography and ultrasound alone.

In addition, fast breast MRI is seemingly equivalent to conventional MRI. A conventional MRI is the best test for finding breast cancer but is expensive and limited to high-risk patients. However, since fast breast MRI testing is relatively new, it is not currently available at every center that serves breast cancer screening.

Limitations of Ultrasounds

Limitations to breast ultrasounds include:

  • Unable to view the entire breast: Ultrasounds are conducted using a handheld transducer that slides across the skin to identify an abnormality. As a result, the whole breast cannot be thoroughly evaluated.
  • Cannot examine deep breast tissue: Ultrasound helps evaluate superficial lumps, but a mammogram can better assess abnormalities deep in the breast tissue.
  • Does not evaluate the axillary lymph nodes (armpits): Evaluation of the axillary lymph nodes (divided into three levels: the lower, middle, and upper part of the armpit) helps determine if breast cancer has traveled beyond the breast. When breast cancer is in the axillary lymph nodes they become swollen and larger than normal. If breast cancer is found in the axillary lymph nodes it could mean the disease has metastasized (spread) to other parts of the body.

Both mammograms and ultrasounds are subject to user error. One study found that radiologists (doctors who analyze imaging tests) missed 10%–30% of breast cancers seen on mammograms. Additionally, the operator's skill level can significantly affect the accuracy of a breast ultrasound result.

The Right One for You

Several factors help your healthcare provider choose which test is best for you, including:

  • Risk factors: Family history of breast cancer or inherited genetic mutations like breast cancer gene 1 and breast cancer gene 2 (BRCA 1 and BRCA 2, respectively) puts you at higher risk for developing breast cancer. You will likely need yearly mammograms before the age of 40.
  • Breast density: Having dense breasts makes finding breast cancer more difficult and increases the risk of developing breast cancer. Having a mammogram, ultrasound, and possibly an MRI can improve the accuracy of breast cancer screening for women with dense breasts.
  • Age: Women at average risk for breast cancer can begin yearly mammograms at the age of 40. At 55, mammograms can be spaced out in every other year.
  • Palpable lump: There are times when an ultrasound may be appropriate for breast cancer screening. When a palpable lump (one that can be felt by touch) exists but the mammogram is normal, ultrasound can be used to determine the likelihood of cancer.

Other Imaging Technologies

Neither mammograms nor breast ultrasounds will find all breast cancers. Other options may be available for women at high risk of developing breast cancer.

One such option is breast magnetic resonance imaging (breast MRI), which uses powerful magnetic and radio waves to generate highly detailed images, especially of the soft tissue. Breast MRI may be the most appropriate choice for young women with dense breasts who have significant risk factors for breast cancer.

Other tests include elastography (measures the stiffness of breast tissue), digital mammography (uses less radiation than conventional mammograms), and optical mammography without compression (uses infrared light instead of X-ray).

Breast thermography can spot temperature variations suggestive of cancer. Cutting edge as it may seem, a 2016 study concluded that at present "thermography cannot substitute for mammography for the early diagnosis of breast cancer."

These techniques continue to evolve as researchers look for better ways to find breast cancer in the earliest stages of the disease.

A Word From Verywell

Mammograms remain the gold standard for screening, diagnosing, and following up after breast cancer. However, breast ultrasounds play an essential role in identifying breast cancer as well.

If a suspicious mass is discovered on a mammogram, a breast ultrasound can help further evaluate that area. Women with dense breasts may need both mammograms and ultrasounds. Unfortunately, neither mammograms nor ultrasounds are 100% accurate. Therefore, being familiar with your breasts and reporting unusual changes is the first step in early detection.

Frequently Asked Questions

  • Is a breast ultrasound better than a mammogram?

    Mammograms are better for breast cancer screening, but ultrasounds are valuable in evaluating changes in the breast tissue.

  • Can a breast ultrasound detect cancer?

    Breast ultrasounds help detect whether a mass looks concerning for cancer or not. They also identify suspicious activity in dense breast tissue better than mammograms.

  • What does a breast ultrasound show that a mammogram doesn't?

    Breast ultrasounds can determine if a mass is fluid-filled (not likely cancer) or is solid. They also help identify lumps that may be present by touch but don't show on a mammogram.

  • Can an ultrasound tell if a breast lump is benign (noncancerous)?

    If the ultrasound determines the mass is fluid-filled, it's likely not breast cancer. However, having the lump biopsied (removing a sample of tissue to be examined in the lab) is the only sure way to know if it's cancerous.

Originally written by
Pam Stephan
Pam Stephan is a breast cancer survivor.
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