The sternalis is an uncommon, variant muscle of the anterior thoracic wall that is estimated to be present in 8% of the human population. Students in a medical gross anatomy course were fortunate to discover a right, unilateral sternalis muscle during dissection of a female cadaver. Despite its rarity, radiologists must be aware of the possibility of encountering the sternalis during thoracic imaging (CT scans, mammography, MRI) because of the risk for its misdiagnosis as a tumor. Further, risk for surgical complications such as damage to this muscle during breast surgery must be considered. Thus, although it may be difficult to perform a proper anatomic analysis of the infrequently observed sternalis muscle, it is important that students and clinicians be aware of its existence because of its potentially significant impact on clinical diagnosis and patient management.
