What is the next step in evaluating an asymmetry in the central breast at mid depth, visible on the craniocaudal (CC) view?

Evaluation of Mammographic Asymmetry on CC View

Proceed immediately with diagnostic mammography including spot compression views to determine if the asymmetry persists or represents summation artifact, followed by targeted ultrasound of the area of concern. 1, 2

Diagnostic Algorithm

Step 1: Diagnostic Mammography with Additional Views

• Obtain spot compression views to determine whether the asymmetry persists or disappears (indicating summation artifact from overlapping normal breast tissue). 3, 1, 2
• Add magnification views to evaluate for any associated microcalcifications that may not be visible on standard views. 1, 2
• Consider lateral or rolled views to fully localize the asymmetry in three-dimensional space. 4

Step 2: Targeted Ultrasound

• Perform concurrent targeted ultrasound of the area corresponding to the mammographic asymmetry to identify potentially benign causes (such as cysts or fibroadenomas) or to identify a target for biopsy if suspicious features are present. 3, 1, 2
• Use a high-resolution linear-array transducer with minimum center frequency of 10 MHz. 3
• Ultrasound identifies additional lesions not visible on mammography in 63-69% of symptomatic cases. 2

Critical Decision Points Based on Findings

If Asymmetry Disappears on Spot Compression

• The finding represents summation artifact from normal overlapping breast tissue and can be classified as BI-RADS 1 (negative). 2, 5
• Return to routine screening. 1

If Asymmetry Persists on Spot Compression

BI-RADS 3 (Probably Benign):

• Clinical re-examination in 3-6 months. 1
• Follow-up imaging with diagnostic mammogram and/or ultrasound every 6-12 months for 1-2 years to assess stability. 1
• If stable after this period, return to routine screening. 1

BI-RADS 4-5 (Suspicious or Highly Suggestive of Malignancy):

• Tissue biopsy is mandatory using core needle biopsy (preferred method) or needle localization excisional biopsy. 1, 2
• If ultrasound identifies a correlate, perform US-guided core biopsy (easier to tolerate, no radiation, allows access to posterior lesions). 3
• If no ultrasound correlate is identified, perform stereotactic-guided core biopsy under mammographic guidance. 3, 4

Important Clinical Context

Cancer Risk Considerations

• Developing asymmetry (new or increased compared to prior) has a positive predictive value of 12.8% for cancer at screening and 42.9% when biopsy is recommended. 1
• 23.8% of cancers presenting as developing asymmetry had no sonographic correlate, emphasizing that lack of ultrasound findings does not exclude malignancy. 1
• Low and intermediate-grade DCIS can present as asymmetry without calcifications. 1

Performance Characteristics to Remember

• Mammography alone has relatively low sensitivity (15-68%) for detecting malignancy in symptomatic presentations. 2
• The negative predictive value of ultrasound for breast cancer in patients with focal asymmetric density is 89.4%, but absence of a suspicious sonographic finding does not exclude malignancy. 6

Critical Pitfalls to Avoid

• Never dismiss asymmetry without spot compression views, as summation artifact must be excluded before providing reassurance. 2
• Do not rely on mammography alone—ultrasound is essential as it identifies additional lesions in the majority of cases. 2
• Do not skip biopsy based on negative ultrasound alone if the mammographic finding is suspicious (BI-RADS 4-5), as nearly one-quarter of cancers presenting as asymmetry have no ultrasound correlate. 1, 6
• Ensure appropriate follow-up even with BI-RADS 3 assessment, as short-interval follow-up for 1-2 years is necessary to confirm stability. 1, 2
• Recognize that normal mammography and ultrasound do not exclude malignancy, particularly for small or purely intraductal lesions. 2