Submit Manuscript | http://medcraveonline.com Abbreviations: SM, sternal muscle; SCM, sternocleidomastoid muscle; PMM, pectoralis major muscle Introduction The sternal muscle also called ‘presternalis,’ sternalis, rectus sterni or ‘sternalis brutorum,’ ‘thoracicus’ 1 is an interesting case of anatomical variation, being described in the literature as a small and irregular subcutaneous muscular mass, located superfcially to the sternum bone and the pectoralis major muscle, 2 being present in about 4% to 7% in whites, 8.4% in blacks and 11.5% in Asian populations 3 and can be found both uni and bilaterally. 4 The muscle was frst described in 1604, and it is still a topic of debate in the scientifc community, especially in relation to its function, vascularization, innervation, as well as its variety of arrangements in its fxation sites along the chest. 2 It is known in the literature that the main fxation sites for this muscle are: proximally, the tendon of the sternal portion of the sternocleidomastoid muscle, 5–7 pectoralis major fascia, 6 manubrium of the sternum, 4,8 and aponeurosis of the external oblique muscle of the abdomen, 6,9,10 and distally, the sheath of the rectus abdominis muscle at the level of the xiphosternal joint, 10 aponeurosis of the external oblique muscle, 2 and from the 5th to the 7th costal cartilages. 5,11 Its presence varies from a few short fbers to a well-formed sternal muscle, found unilaterally or bilaterally. Jelev et al., 8 studying the sternal muscle in the Bulgarian population and based on the belly morphology of the sternal muscles, observed in the literature eight variations, which were classifed into two types: type I, unilateral sternal muscle and type II, bilateral sternal muscle and both encompassing four subtypes. However, there is also a wide variation in height (4.8 ± 1.97 cm), width (15.1 ± 6.84 mm) and thickness (3 ± 0.91 mm). 12 The vascularization of the sternal muscle has been little reported in the literature, but for Jelev et al., 8 this irrigation is performed by the perforating branches of the internal thoracic artery. Its innervation is performed by the medial or lateral pectoral nerves, 8 intercostal nerves 8,13 or by both. 14 Clinically, the sternal muscle can be confused with several benign or malignant lesions, especially breast tumors. 15 Hence, mastologists must be aware of these anatomical variants to distinguish between normal structures and lesions that can represent breast cancer. Therefore, the objective of our work is to report the existence of and describe the sternal muscle in an adult melanodermic female cadaver. Case report During a routine dissection, at the Anatomy Laboratory of the Morphology Department of the Federal University of Sergipe, of a female adult human corpse with approximately 40 years old, a sternal muscle (Figure 1) was found on the anterior wall of the right hemitorax, oblique in direction and lying on the sternal origin of the pectoralis major muscle. It originated from an arch between the two origins of the sternocleidomastoid muscle and its insertion was fxed into the 3rd, 4th and 5th right costal cartilages, mainly the 5th. The muscle length was 10.8 cm, 6.7 cm in its muscular portion and 4.1 cm in its tendinous portion. Its maximum width was 1.7 cm in its tendinous part and 2.1 cm in its muscular part. It was not possible to observe the innervation of the sternal muscle, because the branches of the pectoral nerves were easily damaged as they were mistaken for connective tissue during dissection. Discussion The sternal muscle is an anatomical variant of the anterior chest wall, 16 often described as remnants of the feshy panicle (panniculus carnosus) 6 and its presence is still a dilemma in the diferential diagnosis for radiologists as well as for surgeons, 17 as far as concerns to breast tumors. Its occurrence in humans varies from 3.1 to 23.5%, 8 although its prevalence is directly infuenced by sex. According to data in the literature, its prevalence is higher in women than in men, which is in accordance with our case, as well as that of other authors. 2,8,9,15 Regarding ethnicity, it is more frequent in the Asian population, 3,18 specially in the Indians. 8 MOJ Anat Physiol. 2021;8(1):20‒22. 20 ©2021 Aragão et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and build upon your work non-commercially. Unilateral sternal muscle in an adult melanodermic cadaver Volume 8 Issue 1 - 2021 José Aderval Aragão, 1,3 Isaias Felipe dos Santos, 1 Willian Moreira Leão e Silva, 1 Iapunira Catarina Sant’Anna Aragão, 2 Felipe Matheus Sant’Anna Aragão, 2 João Victor Andrade Pimentel, 1 Danilo Ribeiro Guerra, 1 Francisco Prado Reis 3 1 Department of Morphology, Federal University of Sergipe (UFS), Brazil 2 Medical School, University Center of Volta Redonda (UNIFOA), Brazil 3 Medical School of Tiradentes University (UNIT), Brazil Correspondence: José Aderval Aragão, Federal University of Sergipe, Marechal Rondon Avenue, São Cristóvão, Sergipe, Brazil, Tel +55-79-991916767, Email Received: February 23, 2021 | Published: May 17, 2021 Abstract The sternal muscle, also known as sternalis, rectussternal, parasternal or japonicus is a curious case of anatomical variation of the anterior chest wall. During a routine dissection, a muscle mass related to the sternum was found in the anterior wall of the right hemithorax in a melanodermic female cadaver. The literature, its incidence is mentioned to vary from 3.1 to 23.5%, and little is known about its function with divergences regarding its origin, insertion, innervation and vascularization. Clinically, some mastologists report that this fnding is often confused with a tumor, making it difcult to distinguish between normal structures or lesions that symbolize cancer. Keywords: sternalis, chest, breast, surgery, radiography, mammogram MOJ Anatomy & Physiology Case Report Open Access