Aneurysm of the azygos vein is exceedingly rare and few cases have been described in the literature. The first one was reported in 1981 by Barraine et al. (6). The importance of the aneurysm of the azygos vein might be due to its appearance as an incidental finding in imaging studies. It is considered in the differential diagnosis of a mass in the area of the right tracheobronchial angle or of an enlargement of the right upper or posterior mediastinum. Dynamic computed tomography and MRI are very important in diagnosing this abnormality and confirming its anatomical relationships (1, 3, 5).
There are three main causes of azygos vein aneurysm. Most reported cases are secondary to trauma including blunt injury or catheter insertion into the azygos vein.
The other one is azygos vein dilatation caused by pressure and volume load secondary to congestive heart failure, obstruction of the superior or inferior vena cava, congenital anomalies of the inferior vena cava like agenesis and thrombosis, portal hypertension, pregnancy and pulmonary sequestration with azygos drainage. This type of aneurysm is usually fusiform (1, 2, 4). Some believe a congenital origin for azygos aneurysm as the third reason. Abnormal development of forming vessels of the azygos vein, right supracardinal and the proximal portion of the posterior cardinal vein can be suggested as a cause of idiopathic azygos vein aneurysm (4, 5). It usually presents as an asymptomatic mass (4, 5). Symptoms depend on the size of the aneurysm. When the aneurysm is enlarged, the mass effect on the esophagus, bronchus and superior vena vena cava are successively prospected. Pulmonary embolism as a result of thrombus formation within the aneurysm can be the potential complication (1).
On chest X-ray, a well-defined mass is revealed in the right tracheobronchial angle that has a variable size during inspiration or the Valsalva maneuver. Depending on the size of the neck of the aneurysm, there is only slight enhancement of the mass in the early phase, but homogeneous enhancement in the late phase on dynamic computed tomographic images (1, 3, 5). MR images are variable based on the neck width of the aneurysm; from low signal intensity in both T1 and T2 weighted images in a narrow neck to mixed signal density in wide neck aneurysms. The width of the aneurysmal neck affects the amount of blood flow within the aneurysm (5).
In our case, the mentioned aneurysmal dilatation had a wide neck causing high blood flow in it. Therefore, signal void appearance in all pulse sequences of MRI study could be expected (Figure 3). Treatment of the aneurysm of the azygos vein is controversial. Mostly, the literature has limited surgical intervention to complications such as rupture, obstruction or embolic events (2, 4).
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