title: The sternalis muscle: an unusual normal finding seen on mammography.
abstract: OBJECTIVE
  We studied the appearance of the sternalis muscle on mammography and on CT and MR imaging. To our knowledge, this is the first description of this normal anatomic variant. An approach is provided that permits differentiation of the sternalis from significant pathology.
  
  
  METHODS
  Between January 1992 and December 1994, four women of an estimated 32,000 who had mammograms at the Massachusetts General Hospital had an unusual, irregular structure visible medially on the craniocaudal projection that posed a diagnostic dilemma. The records and imaging studies of these women and two others from the Deaconess Hospital breast imaging program were reviewed to determine the etiology of the findings seen by mammography and to establish a diagnostic approach.
  
  
  RESULTS
  Surgery in one patient and cross-sectional imaging in the other five established that the structure was the sternalis muscle. Although it may be bilateral, the sternalis muscle was visible only unilaterally on the mammograms of these six women. The appearance of the muscle ranged from an irregularly rounded density at the sternal edge of the film to flame-shaped and almost completely surrounded by fat. CT and MR imaging are diagnostic when they show the longitudinal extent of the muscle, which lies anterior to the medial margin of the pectoralis major muscle.
  
  
  CONCLUSIONS
  The sternalis muscle is an unusual variant of the chest wall musculature. It may be visible as a rounded or irregular density on the craniocaudal mammogram along the sternal edge of the film. With improved mammographic positioning it will be seen more frequently. The muscle has a variety of appearances that should be familiar to the radiologist to avoid confusion with a malignant lesion. The etiology can be confirmed and cancer excluded by CT or MR imaging.
authors.affiliation: Department of Radiology, New England Deaconess Hospital, Boston, MA 02114, USA.
authors.forename: F M
authors.initials: FM
authors.lastname: Bradley
authors.forename: H C
authors.initials: HC
authors.lastname: Hoover
authors.forename: C A
authors.initials: CA
authors.lastname: Hulka
authors.forename: G J
authors.initials: GJ
authors.lastname: Whitman
authors.forename: K A
authors.initials: KA
authors.lastname: McCarthy
authors.forename: D A
authors.initials: DA
authors.lastname: Hall
authors.forename: R
authors.initials: R
authors.lastname: Moore
authors.forename: D B
authors.initials: DB
authors.lastname: Kopans
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008327:Mammography; D018482:Muscle, Skeletal / Q000002:abnormalities* / Q000000981:diagnostic imaging* / Q000473:pathology; D013902:Radiography, Thoracic; D013249:Sternum / Q000000981:diagnostic imaging