What is the significance of asymmetry on the craniocaudal (CC) view and does it warrant further evaluation on other views such as the mediolateral oblique (MLO) and lateral views?

Asymmetry on Craniocaudal (CC) View: Evaluation Across Multiple Views

Asymmetry seen only on the CC view does not automatically appear on all breast views and requires systematic evaluation with supplemental mammographic projections to determine if it represents true pathology or summation artifact. 1

Understanding Asymmetry Behavior Across Views

Asymmetries visible on a single view are frequently summation artifacts caused by overlapping normal breast tissue rather than true lesions. When breast tissue is compressed differently in CC versus mediolateral oblique (MLO) views, the three-dimensional architecture projects differently onto the two-dimensional image. 2

• True masses persist across multiple projections, while summation artifacts disappear or shift location when the breast is repositioned 2
• Rolled views demonstrate summation artifacts in 74.6% of cases where asymmetry is the primary finding 2
• The ACR recommends obtaining supplemental views including spot compression, magnification, or lateral projections to clarify whether asymmetry represents real pathology 1

Algorithmic Approach to CC-Only Asymmetry

Step 1: Obtain Supplemental Mammographic Views

• Perform rolled CC views by repositioning the breast medially or laterally while maintaining the same X-ray beam angle—this separates overlapping structures and resolves 97.7% of equivocal findings 2
• Add 90-degree lateral views or exaggerated CC views to triangulate the location of any persistent finding 1
• Use spot compression with or without magnification to evaluate the specific area of concern 1

Step 2: Determine Persistence Across Views

• If the asymmetry disappears on rolled or orthogonal views, it represents summation artifact and requires no further workup 2
• If a discrete mass becomes visible on supplemental views, proceed to ultrasound correlation 1
• If microcalcifications become apparent on magnification views, this may indicate ductal carcinoma in situ (DCIS) requiring biopsy 1, 3

Step 3: Ultrasound Evaluation When Indicated

• Perform targeted ultrasound if supplemental mammographic views reveal a persistent mass or architectural distortion 1
• Ultrasound detects 93-100% of cancers occult on mammography and increases overall sensitivity when combined with mammography 4
• The combined negative predictive value of mammography plus ultrasound exceeds 97% 4

Critical Pitfalls to Avoid

Never dismiss asymmetry based solely on single-view imaging—failure to obtain orthogonal or supplemental views can miss true pathology. 1

• Do not proceed directly to biopsy without supplemental imaging, as this leads to unnecessary procedures for summation artifacts 2
• Avoid relying on MLO view alone to exclude pathology when CC asymmetry is present—each view captures different breast tissue architecture 5, 6
• If clinical examination reveals a palpable correlate at the site of asymmetry, imaging findings should never overrule the need for tissue diagnosis 4, 3

Computer-Aided Detection Considerations

Research demonstrates that linking corresponding regions between MLO and CC views improves mass detection accuracy, with correct correspondence established in 82% of cancer cases. 5, 6 This underscores that true lesions typically have correlates in both views, while isolated single-view findings warrant heightened scrutiny for artifact.

• Texture features show less correlation between views for calcifications versus masses (statistically significant difference), suggesting calcifications may appear differently across projections 7
• Two-view analysis improves lesion-based sensitivity from 56% to 61% at 0.1 false positives per image 6