A Rare Case of a Symptomatic Sternalis Muscle: Ultrasonograpy And MRI Correlation

Introduction

Accessory muscles are common, yet often overlooked entities (Sookur PA et al. Radiographics 2008, 2: 481–499) and are most often found in the extremities. While frequently just an incidental finding in radiological examinations like ultrasound or MRI or during autopsy, there are incidences of symptomatic accessory muscles due to muscular imbalances, overuse tendinopathies, presentation as a soft tissue mass (López Milena G et al. Eur. Radiol. 2001, 8: 1487–1489), vascular (Sookur PA et al. Radiographics 2008, 2: 481–499) or neural compression syndromes (Sookur PA et al. Radiographics 2008, 2: 481–499; Paraskevas G et al. Clin. Anat. 2008, 3: 246–251; Kinoshita M et al. Foot ankle Int. 2003, 2: 132–136).

While most case reports and case series describe accessory muscles of the extremities (Sookur PA et al. Radiographics 2008, 2: 481–499; Paraskevas G et al. Clin. Anat. 2008, 3: 246–251; Christodoulou A et al. Br. J. Sports Med. 2004, 6: e38; López Milena G et al. Eur. Radiol. 2001, 8: 1487–1489; Paraskevas GK and Ioannidis O Ital. J. Anat. Embryol. 2011, 1: 45–51; Howe BM and Murthy NS J. Radiol. Case Rep. 2012, 10: 20–25; Kouvalchouk JF et al. Rev. Chir. Orthop. Reparatrice Appar. Mot. 2005, 232–238; Kinoshita M et al. Foot Ankle Int. 2003, 2: 132–136), there are only a few reports on accessory muscles of the thorax. While variations of the pectoral muscles (Natsis K and Totlis T Clin. Anat. 2007, 8: 980–981; Huntington GS J. Anat. Physiol. 1904, Pt 1: 1–54.27) and intercostal muscles (Nelson ML et al. Anat. Rec. 1992, 2: 318–321) often remain without clinical symptoms, accessory muscles of the upper thorax aperture and neck can cause symptoms, such as thoracic outlet syndrome (Singhal S, Vijaya Rao V and Manjunath KY Int. J. Morphol. 2008, 4: 813–815; Forcada P et al. Clin. Anat. 2001, 1: 55–57).

The sternalis muscle has a long history of scientific publications (Snosek M, Tubbs RS and Loukas M Clin. Anat. 2014, 6: 866–884) describing this common variant during autopsy (Arráez-Aybar LA et al. Clin. Anat. 2003, 4: 350–354) or as an incidental finding mainly during mammography (Scott-Conner CEH et al. Clin. Anat. 2002, 1: 67–69) or surgery (Bailey PM et al. Plast. Reconstr. Surg. 1999, 4: 1189–1190). However, to our knowledge, there is no report of a sternalis muscle with clinical symptoms and dedicated sonographic workup.