PS is a rare congenital anomaly classically consisting of the combination of unilateral aplasia/hypoplasia of the sternocostal head of the major pectoral muscle and ipsilateral brachysyndactyly [1–3]. Other usual anomalies in PS are malformations of the anterior chest wall and breast. Dextrocardia, lung herniation, renal, vertebral and lower limb malformations have been described in rare cases [4]. Moreover, reports of PS associated with other known syndromes in the same individual are not uncommon. In fact, associations with Moebius Syndrome, facio-auricolo-vertebral dysplasia and frontonasal dysplasia have been described [5].
The incidence is 1:30.000, with a higher frequency among males [4]. In 75% of the unilateral cases it is located in the right hemithorax [2]. Reports of bilateral agenesis of the muscle have been infrequently reported in literature [4, 5]. Most cases of PS reported are sporadic; however familiar cases have been occasionally described. The possible mechanism suggested is a paradominant inheritance in which mutations can be transmitted through many generations in the absence of an apparent phenotype [5].
The cause of PS is unknown; however, it is believed that in the embryonic development, during the sixth week of pregnancy, a momentary interruption or reduction in the circulation of the subclavian and vertebral arteries of one of their peripherical ramifications primes the pathogenetic mechanism of the syndrome and results in different degrees of severity depending on the length and intensity of the vascular interruption [2].
The diagnosis is generally postnatal. There are only two reports in which the diagnosis is made prenatally. In case of a dextroposition in the fetus, it would be important to consider PS in the differential diagnosis. In these cases, sonographic evaluation should also include a focused examination of the rib cage [6].
Because clinical features are highly variable and not all present in the same individual, patients with PS should undergo an accurate physical examination and investigations to exclude renal, cardiac, or other important anomalies.
Patients with significant deformities of the chest wall and overlying soft tissue may need surgical reconstruction, generally recommended after the completion of growth. Emergency surgery is reserved for a very rare subset of children with compromised respiratory function [4].