[Sternalis muscle simulating a breast nodule].

Purpose: To report a series of three cases of a normal variation known as sternal muscle, simulating a breast lesion.

Methods: The diagnostic suspicion was based on the clinical picture, findings in the physical examination and imaging, being confirmed by sectional imaging methods such as computerized tomography (CT) and magnetic resonance imaging (MRI). A review of the literature has been made in the data Medline and in breast radiology textbooks about the anatomic, clinical and imaging aspects of the sternal muscle.

Results: Three female patients, without complaints, who presented nodular breast lesions in the medial quadrants projection (two in a routine mammographic exam and one in a computerized tomography). The diagnosis of sternal muscle was confirmed through breast MRI or through thoracic CT, showing an elongated image in the left parasternal region, adjacent to the breast muscle.

Conclusions: The sternal muscle is an unusual variation of the muscles of the thoracic wall, present in about 2 to 8% of the population. The knowledge of this entity is crucial, as it can simulate a breast node.