Pectus excavatum or Pectus carinatum: These are congenital conditions that affect the shape of the chest wall, leading to asymmetry. Pectus excavatum is a sunken chest, while pectus carinatum is a protruding chest. They are relatively common and can be diagnosed based on physical examination and imaging studies.

Scoliosis: A condition characterized by an abnormal lateral curvature of the spine, which can cause chest asymmetry due to the rotation and deformity of the thoracic cage.
Muscular atrophy or hypertrophy: Asymmetrical development or atrophy of the chest muscles (e.g., pectoralis major) can lead to noticeable chest asymmetry.
Previous thoracic surgery or trauma: Scarring or deformity from previous surgeries or injuries to the chest wall can result in asymmetry.

Lung cancer or metastasis: Although less common, a new onset of chest asymmetry could be a sign of a underlying malignancy, such as lung cancer, which can cause asymmetrical growth or destruction of lung tissue.
Pneumothorax: A collapsed lung can lead to chest asymmetry due to the difference in lung volume between the two sides. This is a medical emergency requiring prompt diagnosis and treatment.
Thoracic aortic aneurysm or dissection: These are life-threatening conditions that can cause chest asymmetry among other symptoms. Early diagnosis is crucial for survival.

Poland syndrome: A rare congenital condition characterized by underdevelopment or absence of the pectoralis major muscle on one side of the body, leading to noticeable chest asymmetry.
Jeune syndrome: A rare genetic disorder that affects the development of the bones, including those in the chest, leading to asymmetry and other skeletal abnormalities.
Asymmetric chest wall deformities due to neurofibromatosis: In some cases, neurofibromatosis type 1 can cause asymmetric growth of the chest wall due to the presence of neurofibromas.