Aneurysm of a pulmonary artery branch: an uncommon cause of a coin lesion.

We report the case of a 26-year-old woman with ventricular septal defect associated with a typical coin lesion as shown on the chest roentgenogram. Selective angiography revealed the coin lesion to be caused by an aneurysm of a tertiary pulmonary arterial branch. In addition, two smaller aneurysms were noted. It is postulated on clinical and histologic grounds that the aneurysms were caused by congenital weakness of the pulmonary arterial wall in conjunction with increased pulmonary flow and slightly elevated pulmonary arterial pressure.