Musculus Sternalis: A Normal but Rare Mammographic Finding and Magnetic Resonance Imaging Demonstration

Abstract

A spiculated triangular opacity with irregular contours was detected in the craniocaudal screening mammogram of a 47-year-old woman with positive family history of breast carcinoma (Fig. 1). Magnetic resonance imaging (MRI) demonstrated sternal muscle paralleling the pectoralis muscle (Fig. 2).Bilateral lobulated heterogeneous opacities containing fatty tissue, were detected on the medial quadrants of the craniocaudal mammograms of a 50-year-old woman undergoing mammographic screening (Fig. 3). MRI revealed sternal muscle that was more prominent on the right side (Fig. 4).Mediolateral oblique mammograms and ultrasonographic examination were within normal limits in both patients.Musculus sternalis is a rare anatomic variation of the chest wall that may mimic a malignant mass lesion on the medial aspect of craniocaudal mammograms. The sternal muscle originates from the rectus abdominis muscle and enters at the medial or lateral head of the sternocleidomastoid muscle and overlies the pectoralis muscle. MRI demonstrates the sternal muscle and helps to exclude possible malignant mass lesions.

Two Cases of Rectus Sternalis Muscle

“…The sternalis muscle, when present appears as a flame shaped or speculated triangular structure on the medial aspect of craniocaudal projections [23]. Identification and recognition of this rare anatomical variant can reduce the chances of misdiagnosis, avoid subsequent diagnostic procedures like biopsies, and also misinterpretation as recurrence at a later date [4].…”

“…Identification and recognition of this rare anatomical variant can reduce the chances of misdiagnosis, avoid subsequent diagnostic procedures like biopsies, and also misinterpretation as recurrence at a later date [4]. Sternalis muscle when present can mimic a focal density and its presence can be confirmed by MRI or CT imaging [23].…”

Back to the Debate: Sternalis Muscle

“…SM has been discovered on mammography, magnetic resonance imaging (MRI), and computed tomography (CT). Bradley et al (1996) found 4 cases out of an estimated 32000 mammograms that gave signals at the position of SM while Goktan et al (2006) and Nuthakki et al (2007) identified SM cases using mammography and MRI. Young Lee et al (2006) encountered 86 cases out of 1387 CT chest scans where 7.3% of the cases were female, and 5.3% were male.…”

Mammographic features and approach to the sternalis muscle

“…The muscle is isodense with fibroglandular densities and can be seen with varying diameters, shapes and contours on mammograms (9). The obtuse angle at the chest wall is typical of a muscular structure, and it is usually surrounded by fat (10).…”