Pectus excavatum is a common congenital chest wall deformity affecting the sternum, also known as the breastbone. It is characterized by an inward depression or “caved-in” appearance of the chest, which can range in severity from mild to pronounced. This condition is the most common congenital chest wall abnormality, observed in approximately 1 to 8 out of every 1,000 live births, and is more frequently identified in males.
Normal Chest Wall Development
The human chest wall forms a protective, flexible cage around vital organs like the heart and lungs. It primarily consists of the sternum at the front, twelve pairs of ribs that wrap around the sides, and the thoracic vertebrae at the back. Costal cartilages connect the ribs to the sternum, allowing flexibility for breathing. This intricate structure enables the chest wall to expand and contract, facilitating normal breathing.
The Mechanism of Inward Growth
Pectus excavatum primarily arises from an abnormal growth pattern of the costal cartilages that connect the ribs to the sternum. Instead of normal growth, these cartilages grow excessively and push the sternum inward. This overgrowth leads to the characteristic depression of the breastbone, often affecting the lower sternum and adjacent ribs.
The inward buckling of the sternum can be symmetrical, forming a cup-shaped concavity, or asymmetrical, involving a broader depression or even a rotated sternum. While the exact cause for this overgrowth is still being researched, the physical manifestation of the deformity often becomes more pronounced during periods of rapid growth, such as puberty. This suggests that the underlying structural anomaly interacts with normal growth processes to determine the severity of the condition.
Underlying Contributing Factors
The factors that contribute to the abnormal cartilage growth seen in pectus excavatum are complex and not fully understood. A familial tendency is observed in over 40% of cases, suggesting a genetic component. While specific genes have not been definitively identified, research continues into the genetic markers that may predispose individuals to this condition.
Pectus excavatum can also occur in conjunction with certain genetic syndromes that affect connective tissue or skeletal development. These include Marfan syndrome, Ehlers-Danlos syndrome, and Noonan syndrome. These associated conditions often involve widespread connective tissue weakness, which may play a role in the development of chest wall deformities. In many instances, however, pectus excavatum appears without any clear genetic link or association with a known syndrome, a situation called idiopathic. While some contributing factors are recognized, the precise origin of the deformity remains unknown in many cases.