The left sternalis muscle variation detected during mastectomy.

The sternalis muscle variation is a well-known anatomical situation. It is present in 8.7% of women and 6.4% of men, although the incidence varies according to sex, race and ethnicity. During a left modified radical mastectomy operation on a 46-year-old female patient a sternalis muscle was detected on the pectoralis major muscle in the superficial fascia. It was in craniocaudal position and was parallel to the body of the sternum. The cylindrical muscle was approximately 8 cm in length and 2 cm in diameter. Such variations are considered to have their origin in embryological development. Awareness of muscular variations and their identification is important both for procedure through the proper dissection planes during breast surgery and in radiological examination and follow-up.