An asymmetry is a discrete area of fibroglandular tissue with no mirror-image correlate in the contralateral breast; unlike a mass, all asymmetry types have concave outward borders and are usually interspersed with fat

There are 3 types

1. Asymmetry: Area of fibroglandular tissue visible on only 1 view; most commonly superimposition of normal breast tissue

2. Focal Asymmetry: Asymmetry seen in 2 views; a real finding (not superimposed tissues); must be differentiated from a mass

3. Developing Asymmetry: New, larger, or more conspicuous asymmetry than on prior imaging; buzzword for malignancy

(Georgian-Smith 2014)