Azygos vein abutting the posterior wall of the right main and upper lobe bronchi: a normal CT variant.

In 9% of 78 normal computed tomographic examinations, the azygos vein was interposed between the posterior wall of the right-main or right-upper-lobe bronchi and lung in the azygoesophageal recess. Observation of the azygos vein on contiguous scans will generally allow a confident identification of this normal variant. Contrast enhancement will elucidate difficult cases.