Carcinoma mimicked by the sternal insertion of the pectoral muscle.

A prospective study of 1843 patients was performed to identify the frequency of imaging the medial portion of the greater pectoral muscle on the craniocaudal projection during routine mammography. This artifact was seen in 14 patients. None of these patients had a palpable abnormality; additional craniocaudal views revealed continuity of the density with the pectoral muscle. Four patients were reexamined in 6 months; no change was seen in the size of the density. The density is thought to represent the medial portion of the pectoral muscle, which is included because of vigorous retraction of the breast and slight external rotation during positioning for the craniocaudal view. Familiarity with the appearance of the medial portion of the greater pectoral muscle on craniocaudal mammograms will help prevent inaccurate interpretations and unnecessary biopsies.