Poland syndrome is a disorder in which affected individuals are born with missing or abnormal muscles on one side of the chest wall. Most individuals with Poland syndrome also have abnormalities of the hand, which often involve shortened fingers, partial fusion of the fingers, or both. The hand abnormalities usually affect the same (ipsilateral) side of the body as those of the chest. Poland syndrome affects the right side of the body more often than the left side.
People with Poland syndrome are missing part of one of the major chest muscles, called the pectoralis major. In most affected individuals, the missing part is the large section of the muscle that normally attaches to the upper arm on one side and the breastbone (sternum) on the other. Other abnormalities may occur on the affected side of the torso. In some cases, additional muscles in the chest wall, side, and shoulder are missing or underdeveloped. There may also be rib cage abnormalities, such as shortened ribs, and the ribs may be noticeable due to less fat under the skin (subcutaneous fat). Breast and nipple abnormalities may also occur, and underarm (axillary) hair is sometimes sparse or abnormally placed. In most cases, the abnormalities in the chest area do not cause health problems or affect movement.