Pectoralis Major Agenesis (Amyoplasia) in a Young Man

June 1, 2008

A 23-year-old man's right chest shows a common congenital muscle anomaly-partial absence of the pectoralis major muscle. The abnormality was noted during a routine preemployment physical examination. The clavicular origin seemed to be intact. There was no apparent decrease in shoulder internal rotation or adduction strength, and the patient had not noticed any shoulder weakness or limitation in motion.

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A 23-year-old man's right chest shows a common congenital muscle anomaly-partial absence of the pectoralis major muscle. The abnormality was noted during a routine preemployment physical examination. The clavicular origin seemed to be intact. There was no apparent decrease in shoulder internal rotation or adduction strength, and the patient had not noticed any shoulder weakness or limitation in motion.

Partial or complete absence of the pectoralis major muscle can be part of Poland syndrome, which consists of hand abnormalities, such as syndactyly, and hypoplasia of the ipsilateral nipple, areola, and chest wall structures. Other than the indentation in the pectoral region, this patient had no other anomalies. His nipples and areolae appeared symmetrical, although periareolar hair growth was noticeably less on the right compared with the left.

The absent muscle is usually compensated for by the adjacent muscles, in this case the pectoralis minor. Reduction in shoulder strength is possible in affected persons; however, significant loss of function is unlikely.