Enlargement of collateral vessels (arteries, veins)

Coarctation of aorta

Interrupted aortic arch

Subclavian artery obstruction (Takayasu’s disease)

Blalock–Taussig shunt (upper two ribs)

Superior vena cava obstruction

Intercostal nerves (neurogenic tumours) (schwannoma, neurofibromatosis type 1)

Hyperparathyroidism