Muscular variant presenting as an asymmetry on mammogram

Anatomic variants in chest wall musculature can pose a potential diagnostic dilemma when visible on a mammogram. A few variants have been commonly reported in the literature and can be confidently identified by appearance and location. We present a case of a pectoralis muscle variant, not previously described in radiology literature that presented as a unilateral asymmetry on a screening mammogram. This article reviews common imaging appearances of muscular variants seen mammographically and provides a diagnostic algorithm to avoid unnecessary workup or biopsy.