The main abnormality on the frontal chest x-ray is an ovoid opacity in the right tracheo – bronchial groove. This is enlarged azygous vein.

This patient had a complete thrombotic obstruction of the inferior vena cava (IVC). The azygous vein, having taken over the IVC drainage, is enlarged. The right para tracheal opacity seen on the chest x-ray is where the severely dilated azygous vein drains into the superior vena cava.

A list of causes of enlarged azygous vein can be found here