Computed tomography appearance of idiopathic aneurysm of the azygos vein.

True idiopathic aneurysm of the azygos vein is a rarely described abnormality. The authors present a case of this anomaly in a 70-year-old woman with a history of rectal carcinoma. The aneurysm was found incidentally on computed tomography, performed to characterize the appearance of a lung nodule. The aneurysm decompressed when the patient was upright. The effects of respiratory and postural manoeuvres on the lesion are discussed and the computed tomography appearance is described.