A gap or indentation in the center of the chest wall, around the sternum (breastbone), is often caused by variations in the growth or positioning of the ribs and sternum. The chest is formed by the sternum and ribs, which are connected by flexible costal cartilage. Understanding the underlying anatomy and causes helps determine if the variation is purely cosmetic or has physiological significance. These structural differences are typically related to congenital conditions affecting the normal development of the thoracic cage.
Pectus Excavatum The Most Common Cause
The most frequent cause of a noticeable depression in the central chest is Pectus Excavatum (PE), also called funnel chest or sunken chest. This congenital deformity is present from birth, though it may not become visually prominent until later childhood or adolescence. PE is the most common chest wall abnormality, estimated to affect between one in 300 to one in 400 live births.
The underlying cause of PE is the abnormal, excessive growth of the costal cartilage, the flexible connection between the ribs and the sternum. This overgrowth pushes the sternum inward toward the spine, creating the characteristic caved-in appearance. The deformity usually affects the lower part of the sternum, involving the third to eighth ribs. It can be symmetrical or asymmetrical, sometimes shifting the deepest point of the depression to one side.
Although present early in life, the indentation often becomes more pronounced during periods of rapid skeletal growth, such as the adolescent growth spurt. This occurs because of the continued, abnormal cartilage growth while the chest wall expands. The visual presentation of PE ranges widely, from a shallow, mild dimpling to a deep, centralized depression.
The precise reason for the abnormal cartilage growth remains unknown, but a clear hereditary component exists. Approximately 35% to 40% of affected individuals have a family member with a similar chest wall deformity. PE is also observed more frequently in males than in females, sometimes at a ratio as high as 3:1.
Assessing Severity and Physiological Effects
Clinical evaluation determines if the sternal depression compromises the function of internal organs, moving beyond just visual appearance. Severity is objectively quantified using cross-sectional imaging, typically a Computed Tomography (CT) scan or Magnetic Resonance Imaging (MRI). These scans allow clinicians to visualize the degree of sternal displacement and its effect on the heart and lungs.
The primary measurement tool is the Haller Index (HI), which is the ratio of the maximum inner chest width to the shortest distance between the sternum and the spine. A chest without PE typically has an HI of around 2.5. A score of 3.2 or greater is often used as a threshold to classify the condition as moderate to severe, which may indicate the need for surgical correction.
In severe cases, the inward pressure from the sternum can displace or compress the heart. This compression may lead to symptoms such as heart palpitations, an irregular heartbeat, or decreased efficiency in the heart’s ability to fill with blood. The reduced volume of the thoracic cavity can also restrict lung capacity, especially during physical activity.
Individuals with severe PE often report physiological symptoms like shortness of breath during exercise, reduced stamina, and fatigue. Pulmonary function tests measure lung capacity, and echocardiograms assess the heart’s function and position. These tests help establish a direct link between the anatomical severity, measured by the Haller Index, and any measurable functional impairment.
Other Anatomical Causes for a Chest Gap
While Pectus Excavatum accounts for most indentations, a chest gap can also result from rarer congenital malformations or acquired issues. One rare congenital condition is a sternal cleft, a significant defect where the two halves of the sternum fail to fuse completely during embryonic development. This condition is much less common than PE, with an incidence of about 1 in 100,000 live births, and leaves the heart and major blood vessels poorly protected.
A chest depression can also be an acquired effect following certain medical procedures. Open-heart surgery requires a median sternotomy, where the sternum is split vertically and rejoined. In some cases, a secondary Pectus Excavatum may develop post-surgery, often due to challenges in sternal fixation or the formation of dense adhesions behind the sternum.
In other situations, the perception of a gap may be purely an optical effect created by muscle or posture variations. Rib flare, where the lower ribs protrude outward, can give the visual impression of an inward chest concavity, especially in the lower sternal area. This is often a postural distortion related to muscle imbalances, such as weak core muscles or dysfunctional breathing patterns, rather than a bony deformity.
Treatment and Management Options
The approach to correcting a chest wall indentation depends on the severity of the anatomical defect and the presence of physiological symptoms. For mild Pectus Excavatum cases with no compromise to heart or lung function, treatment focuses on non-surgical management. This may involve physical therapy aimed at improving posture, strengthening core muscles, and correcting rib flare to minimize the visual prominence of the indentation.
Vacuum Bell Therapy (VBT) is an increasingly used non-invasive treatment option. This involves placing a cup-shaped device on the chest that uses suction to create negative pressure, gradually pulling the sternum forward. VBT is most effective for younger patients whose chest walls are flexible and pliable, requiring consistent use over one to two years for lasting results.
Surgical correction is reserved for moderate to severe cases, typically those with a high Haller Index or demonstrable cardiopulmonary compromise. The most common procedure is the minimally invasive Nuss procedure. This technique involves inserting a custom-shaped metal bar beneath the sternum through small incisions on the sides of the chest to push the sternum into a normal position.
The Nuss bar remains in place for approximately two to four years before surgical removal. An alternative, more extensive open surgery is the modified Ravitch procedure. This involves making a larger incision, removing the abnormally grown costal cartilage, and repositioning the sternum. Both surgical methods aim to permanently correct the deformity, offering cosmetic improvement and relief from compression-related symptoms.