Causes: Theorized to be of vascular origin in the embryo, Poland syndrome usually occurs sporadically, with rare autosomal dominant familial cases reported.

Classic history and presentation: Poland syndrome is a rare congenital malformation classically described as hypoplasia / absence of the pectoralis major on one side of the chest (more commonly the right side) with ipsilateral hand abnormalities. Currently, diagnosis requires hypoplasia / absence of pectoralis major with at least 2 minor criteria:

• Hypoplasia or absence of the breast
• Absence of the nipple
• Absence of axillary hair
• Absence of adjacent muscles (eg, serratus anterior, latissimus dorsi, external oblique, deltoid, pectoralis minor, supraspinatus, and infraspinatus)
• Absence of costal cartilage and anterior ribs
• Axillary webbing
• Ipsilateral brachydactyly, brachysyndactyly, or amelia

Prevalence:

• Age – Present from birth. In mild variants involving females, Poland syndrome may only be noticed when there is a unilateral absence of breast growth during puberty.
• Sex / gender – There is a male-to-female ratio of 3:1.

Pathophysiology: The etiology of Poland syndrome remains unclear. The leading theory suggests that interruption of the embryonic blood supply in the 6th week of gestation leads to hypoplasia of the subclavian artery or its branches. The location / severity of the impaired blood flow determines the structures that are compromised (eg, brachial artery leading to hand abnormalities, internal thoracic artery leading to the absence of the sternocostal head of the pectoralis major).

Grade / classification system: Due to the variable presentation of Poland syndrome, there is not one universally used classification system. The syndrome can be defined as mild, moderate, or severe based on breast and anterior thoracic abnormalities that affect reconstruction.