Pectus Carinatum is a chest wall deformity where the breastbone, or sternum, protrudes outward, creating a noticeable convexity in the chest. This condition, often referred to as “pigeon chest,” is a structural variation that is typically benign but can cause significant self-consciousness for those affected.
Defining Pectus Carinatum
Pectus Carinatum (PC) is an anatomical classification of a chest wall deformity resulting from the excessive growth of the costal cartilage connecting the ribs to the sternum. While the deformity can be present at birth, it usually becomes distinctly apparent during periods of rapid growth, such as adolescence.
The deformity is categorized into two main types based on the sternal segment involved. The chondrogladiolar type is the most common, accounting for approximately 95% of cases, and involves the outward protrusion of the body of the sternum and the attached costal cartilages. The less frequent chondromanubrial type, sometimes known as Pectus arcuatum, is characterized by a protrusion of the upper sternum (manubrium) while the lower part may be depressed.
Global and Specific Prevalence Rates
Pectus Carinatum is a less frequently encountered chest wall deformity compared to its counterpart, Pectus Excavatum (sunken chest). Global estimates for PC incidence typically range from about 1 in 1,000 to 1 in 2,500 live births, making PC two to four times less common than Pectus Excavatum.
The true prevalence is challenging to pinpoint, as some studies using advanced imaging have suggested that milder, often undiagnosed forms may be present in up to 5% of the population. Reporting can also vary significantly by region; for instance, some studies conducted in Brazil have shown a higher prevalence of Pectus Carinatum than Pectus Excavatum within the studied population.
Demographic and Genetic Factors
Pectus Carinatum exhibits a pronounced sex disparity, with males affected far more often than females. The male-to-female ratio is generally reported to be approximately 4:1, though some sources suggest a ratio as high as 7:1. This male predominance is believed to be linked to hormonal influences and the rapid skeletal growth that occurs during puberty, which often exacerbates the underlying deformity.
The condition typically becomes obvious in late childhood or early adolescence, with the onset commonly observed between the ages of 11 and 14, coinciding with pubertal growth spurts. While the majority of cases are considered sporadic, PC does have a recognizable hereditary component. About 25% to 33% of affected individuals report a positive family history of a chest wall abnormality, suggesting a genetic predisposition, though the inheritance pattern is often complex and non-Mendelian.
Associated Conditions and Etiology
The underlying cause of Pectus Carinatum is not fully understood, but the leading hypothesis centers on an abnormal overgrowth or growth disturbance of the costal cartilage. This deformity is thought to be a structural manifestation of a systemic issue involving connective tissue integrity.
Pectus Carinatum frequently occurs in isolation, but it is also recognized as a feature of several genetic syndromes that affect connective tissue throughout the body. Conditions such as Marfan Syndrome, Ehlers-Danlos Syndrome, and Noonan Syndrome are often seen alongside Pectus Carinatum. Marfan Syndrome, for example, is caused by mutations in the FBN1 gene, which is responsible for the fibrillin-1 protein, a key component of connective tissue. Furthermore, PC is sometimes associated with other skeletal issues, including scoliosis, a lateral curvature of the spine, in approximately 15% of cases.