Thoracic Wall Muscles

An unusual finding of the pectoralis major muscle: decussation of sternal fibers across the midline

“…Upward of a dozen atypical configurations have been documented in reports in the literature, including the absence of one or more heads or the entire muscle, unusual groupings of heads within the muscle or with surrounding muscles, and the presence of one or more accessory muscles. Absence of the sternocostal head with accompanying hypertrophy of the clavicular head and an absent pectoralis minor is relatively common among aberrations, as is the absence of the entire pectoralis major as a feature of Poland syndrome [ 1 - 3 , 5 , 6 ]. Absence or variation of the abdominal head of the pectoralis major has been well documented [ 1 ].…”

“…Absence of the sternocostal head with accompanying hypertrophy of the clavicular head and an absent pectoralis minor is relatively common among aberrations, as is the absence of the entire pectoralis major as a feature of Poland syndrome [ 1 - 3 , 5 , 6 ]. Absence or variation of the abdominal head of the pectoralis major has been well documented [ 1 ]. Plentiful examples of additional muscles can be found in the literature, for example, an accessory head of the pectoralis major, one or more sternalis muscles, various slips of muscle originating or inserting at unusual locations, and even a double pectoralis major [ 1 - 3 , 6 - 8 ].…”

“…The pectoralis major is composed of three heads: a clavicular head originating from the anterior border of the medial clavicle, a sternocostal head originating from the anterior surface of the sternum and second-sixth costal cartilages, and an abdominal head originating from the aponeurosis of the external oblique [ 1 ]. These three heads insert together as the pectoralis major tendon in the bicipital groove.…”

“…These three heads insert together as the pectoralis major tendon in the bicipital groove. Variations to this general organization are common, occurring six times more frequently than any other muscle or muscle group in the body [ 1 , 2 ]. Herein, we present a case with bilaterally separated clavicular heads and sternal fibers that decussate across the midline.…”

“…Herein, we present a case with bilaterally separated clavicular heads and sternal fibers that decussate across the midline. Variation in the degree of separation between the left and right sternocostal heads as well as interdigitation of the fibers has been described, but complete decussation remains rare [ 1 , 2 ]. Many muscles surrounding the pectoralis major are capable of compensation, so anatomical variations usually produce only minor functional deficits, if they manifest clinically at all [ 3 , 4 ].…”