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The incidence is estimated at 1/30,000, but this is likely an underestimate. It affects more frequently men (male/female ratio of 2:1).

The major feature of Poland syndrome (PS) is complete or partial (sternocostal head) agenesis of the pectoralis major muscle, manifesting as an asymmetric appearance. Generally, the pectoralis minor muscle is also absent. The malformation is typically unilateral with the right side predominantly affected; bilateral involvement is possible but rare (1% of cases). The associated upper limb and rib anomalies determine the severity of PS. According to the combination of these additional features, three forms of PS can be described: type-1 (minimal form) is defined as an isolated pectoral muscle defect, type-2 (partial form) is defined by pectoral muscle defect associated with either upper limb (2a, upper limb variant) or rib (2b, thoracic variant) anomaly, and type-3 (complete form) by pectoral muscle defect associated with both upper limb and rib anomalies. Additional muscle involvement may include the serratus anterior, latissimus dorsi and trapezius. Chest defects can include absence of the anterior part of the rib with lung herniation, rib hypoplasia, contralateral pectus carinatum and/or pectus excavatum. Dextrocardia occurs in 10% of cases, associated with left rib agenesis. Upper limb anomalies are present in 56% of the patients, including brachydactyly, syndactyly or a combination of the two; aplasia/hypoplasia of the middle phalanges of the hand is frequently observed. Hypoplastic/absent hand(s) and short forearm are rarely observed. In all females, the breast and nipple areola complex is aplasitic or hypoplasitic with superolateral localization of the nipple.

The etiology is unknown.

Diagnosis is by clinical evaluation. The pectoral muscle anomaly is generally observed by asking the patient to push the palms of the hands against each other with the arms positioned in front of the body. Cough or other maneuvers increasing thoracic pressure will demonstrate lung herniation in case of rib agenesis. Echography can confirm the diagnosis and delineate the extent of the muscular anomaly and detect cartilage rib anomaly and, in postpubertal females, breast anomaly. Chest X-ray can confirm rib agenesis and dextrocardia.

Differential diagnosis includes other chest wall anomalies, breast/nipple anomalies, isolated thoracic lipoatrophy, and isolated hand/upper limb anomalies without pectoralis major muscle involvement. Syndromes rarely associated with PS include Moebius, Klippe Feil, Pierre-Robin, Sprengel deformity and Carey-Fineman-Ziter.

Antenatal diagnosis is rare; however, suspicion may arise if hand anomaly is detected.

PS is typically a sporadic condition but around 4% of cases are familial. Most cases are probably multifactorial with a low recurrence risk. Autosomal dominant and recessive patterns are described in literature.

Usually, the aim of surgical treatment is cosmetic. However, in a minority of cases thoracic surgery is required to improve respiratory dynamics due to rib cage defect or heart compression by sternal compression. TNB (thorax, breast and nipple) classification guides surgical choice. Patients should be evaluated for surgery at the beginning of puberty (and before complete growth). A combined approach (pediatric/thoracic and plastic surgery) is beneficial. In case of multiple rib agenesis, non-absorbable mesh or metallic or custom prostheses can be used. Breast/pectoral, custom-made, implants can be used to correct the soft tissue and breast defect. Breast/pectoral expander can be used as first step. Fat grafting is beneficial either as first step or to improve final result. For symmetry reasons, surgery to the contralateral breast can be considered. Muscle transpositions require careful evaluation of the benefits and risks, and should only be considered in selected cases and never in children. Correction of syndactyly should generally begin between 12 and 24 months of life. In case of phalangeal absence, non-microvascular free phalangeal transfer from the foot, or microvascular digital transfer from the foot can be proposed.

Aesthetic achievement after surgery is typically satisfactory. Usually, there is not a significant muscle weakness.