What is the difference between a mammogram and a breast ultrasound, and what do they check for differently?

Differences Between Mammogram and Breast Ultrasound

Mammography and ultrasound are complementary imaging methods for breast cancer detection, with mammography being the primary screening tool while ultrasound serves as a valuable diagnostic adjunct that excels at evaluating specific breast abnormalities. 1

Mammography

Technology and Detection Capabilities

• Uses low-dose X-ray imaging to create 2D images of breast tissue
• Standard screening mammography consists of 2 standard views of each breast 1
• Diagnostic mammography includes additional views such as spot compression or magnification views 1
• Excels at detecting:
  • Microcalcifications (which ultrasound cannot reliably detect) 1
  • Architectural distortions 2
  • Early non-palpable cancers

Primary Role

• Gold standard for breast cancer screening 1
• Recommended as the primary screening tool for average-risk women
• Diagnostic mammography is used to evaluate abnormal findings from screening or clinical examination 1

Breast Ultrasound

Technology and Detection Capabilities

• Uses high-frequency sound waves to create real-time images of breast tissue
• Excels at:
  • Distinguishing solid masses from fluid-filled cysts 3, 4
  • Evaluating palpable abnormalities not visible on mammography
  • Detecting cancers in dense breast tissue that may be missed on mammography 5
  • Characterizing masses (shape, margins, internal echoes) 6

Primary Role

• Diagnostic adjunct to mammography 1
• Preferred initial imaging for women under 30 years with breast symptoms 1, 2
• Targeted examination of specific areas of concern 1
• Guidance for interventional procedures (biopsies, cyst aspirations) 4

Key Differences in Clinical Application

Age-Based Recommendations

• Under age 30: Ultrasound is preferred as initial imaging due to increased breast density and radiation concerns 2
• Age 30-39: Either ultrasound or diagnostic mammography is appropriate as initial imaging 2
• Age 40+: Diagnostic mammography recommended as initial imaging, with ultrasound as needed 2

Specific Clinical Scenarios

1. Palpable mass evaluation:

   • Under 30: Start with ultrasound 1, 2
   • Over 30: Start with mammography, followed by ultrasound 1

2. Dense breast tissue:

   • Mammography has reduced sensitivity in dense breasts 5
   • Ultrasound can detect 3-4 cancers per 1,000 women that were missed on mammography 1

3. Cyst evaluation:

   • Ultrasound is definitive for diagnosing simple cysts 4
   • Can characterize cysts as simple, complicated, or complex 1

Comparative Strengths and Limitations

Mammography Strengths

• Superior for detecting microcalcifications (early sign of DCIS) 1, 7
• Better at detecting asymptomatic early-stage cancers 7
• Standardized reporting system (BI-RADS) 1

Mammography Limitations

• Reduced sensitivity in dense breast tissue 5
• Radiation exposure (though minimal)
• Less effective in younger women with denser breasts 1

Ultrasound Strengths

• No radiation exposure
• Real-time imaging allows immediate assessment
• Superior for distinguishing solid from cystic lesions 3, 4
• Better for evaluating palpable abnormalities not seen on mammography 3

Ultrasound Limitations

• Cannot reliably detect microcalcifications 1
• Operator-dependent with variability in technique and interpretation 1
• Higher rate of false-positive findings than mammography 1
• Not standardized as a screening tool 1

Clinical Implications

• Complementary nature: The combination of mammography and ultrasound provides more comprehensive evaluation than either alone 1, 6
• Detection patterns: Some cancers are visible on both modalities, while others may be detected by only one 7
• Tissue sampling guidance: Ultrasound is commonly used to guide biopsies of suspicious masses 4

By understanding the different strengths and limitations of each imaging modality, clinicians can appropriately select and sequence these tests to optimize breast cancer detection while minimizing unnecessary procedures.