What type of breast asymmetry is likely being referred to when an asymmetry is better seen on the craniocaudal (CC) view and warrants further evaluation with spot compression and possible ultrasound?

Mammographic Asymmetry Classification

The asymmetry being described is most likely a "focal asymmetry" or potentially a "developing asymmetry" if it represents a new or changed finding compared to prior imaging. 1, 2

Understanding Asymmetry Types

The American College of Radiology BI-RADS classification defines four distinct types of breast asymmetries, each with different clinical significance 3:

• Asymmetry: Seen in only a single mammographic view and occupies less than one quadrant 4
• Focal asymmetry: Visible in two views, occupies less than one quadrant, and lacks convex borders or mass characteristics 4, 3
• Global asymmetry: Occupies more than one quadrant of the breast 4
• Developing asymmetry: A focal asymmetry that is new or has increased in conspicuity compared to previous mammograms—this carries the highest suspicion for malignancy 5, 6

Why This Case Suggests Focal or Developing Asymmetry

The description indicates the finding is "better seen on CC view" and located in a specific anatomic region (central breast at mid depth), which strongly suggests a focal asymmetry rather than simple asymmetry or global asymmetry. 1, 2

The recommendation for spot compression and ultrasound is the standard diagnostic algorithm for focal asymmetries, as these additional views help determine whether the finding represents true tissue abnormality versus summation artifact 1, 2. Spot compression views will cause summation artifacts to disappear, while true lesions persist 2.

Clinical Significance and Malignancy Risk

If this represents a developing asymmetry (new or increased compared to prior studies), the positive predictive value for cancer is 12.8% at screening and increases to 42.9% when biopsy is ultimately recommended. 1 Notably, 23.8% of cancers presenting as developing asymmetry have no sonographic correlate, emphasizing the importance of mammographic evaluation even when ultrasound is negative 1.

For focal asymmetries without temporal change, the malignancy risk is lower but still requires complete workup 3. Both ductal carcinoma in situ (DCIS) and invasive carcinomas can manifest as asymmetries, and importantly, low and intermediate-grade DCIS can present as asymmetry without calcifications 1, 2.

Recommended Diagnostic Workup

The American College of Radiology recommends the following algorithmic approach 1, 2:

1. Immediate diagnostic mammography with spot compression views to determine if the asymmetry persists or represents summation artifact 1, 2
2. Magnification views if any associated microcalcifications are present 1
3. Targeted ultrasound performed concurrently to identify potentially benign causes or a target for biopsy 1, 2
4. BI-RADS classification based on cumulative findings from all imaging modalities 7

Management Based on BI-RADS Assessment

For BI-RADS 1-3 findings with benign clinical assessment: Clinical re-examination in 3-6 months, with follow-up imaging every 6-12 months for 1-2 years to confirm stability 7, 1

For BI-RADS 4-5 findings: Tissue biopsy is mandatory using core needle biopsy (preferred) or needle localization excisional biopsy 1, 2

Critical Pitfalls to Avoid

Never dismiss an asymmetry without additional views—summation artifact must be excluded with spot compression before providing reassurance 2. The absence of an ultrasound correlate should not preclude biopsy if the mammographic findings remain suspicious after spot compression 1, 5. Approximately 23.8% of cancers presenting as developing asymmetry have no sonographic correlate 1.

Do not rely on mammography alone, as ultrasound identifies additional lesions not visible on mammography in 63-69% of symptomatic cases 2. However, recognize that normal mammography and ultrasound together reduce cancer risk to approximately 0% in the setting of pathologic nipple discharge 8.