Busra Anacur; Eda Savasir; Zeynep Gul & Gursel Ortug

The sternalis muscle, an anatomical variant situated superficial to the pectoralis major muscle, has long been a subject of anatomical curiosity due to its sporadic occurrence and unsettled characteristics, including its embryological lineage and functional role. Therefore, in light of a case of unilateral sternalis, we inspected the existing literature, emphasizing this variant’s importance from an embryologic and clinical standpoint, as well as the muscle's background, source of innervation, and classification. A unilateral sternalis muscle was observed in a 97-year-old male cadaver during routine dissections for educational purposes, displaying distinctive attachments to the sternum and the 4th rib. The variation was photographed, and a digital caliper utilized with a measurement range of 0 to150 mm and an accuracy of 0.02 mm. The muscle was left unilateral and positioned between the upper margin of the 2nd rib and lower margin of the 4th rib, lateral to the sternum and superficial to the pectoralis major muscle. Examining this variation from an embryologic and clinical standpoint, as well as learning about its background, prevalence, innervation, and classification, is critical for both anatomists and clinicians, given the variant's ability to simulate pathological entities on diagnostic imaging and influence surgical planning.

KEY WORDS: Anterior thoracic wall; Anatomical variation; Embryology; Sternalis muscle; Muscular variation.

ANACUR, B.; SAVASIR, E.; GUL, Z. & ORTUG, G. Case report of a unilateral sternalis muscle: Integrating historical perspectives, literature review, and clinical significance. Int. J. Morphol., 43(1):218-225, 2025.