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Findings: Chest radiographs reveal diffuse widening of the mediastinum. Specifically, abnormal soft tissue extends beyond the aortic knob within the left side of the superior mediastinum. In addition, there is a right paratracheal soft tissue prominence, and a prominent rounded contour in the region of the azygous vein.
Chest CT was performed to evaluate the mediastinum. Abnormal soft tissue and gas is seen extending from the left chest wall into the mediastinum, consistent with abscess. On the right, there is a markedly dilated azygous vein, and absence of the infradiaphragmatic and suprahepatic IVC. The renal veins drain into a prominent azygous vein. The left renal vein drains into the azygous vein and is retroaortic.
Diagnosis:Azygous continuation of IVC, IVC absence.
Discussion: In the setting of increased right sided paratracheal soft tissue, enlargement of the azygous vein should be considered. This enlargement can be secondary to IVC or SVC thrombosis, but can also be secondary to primary aneurysmal dilatation of the azygous vein. As seen in our case, it is important to consider azygous vein enlargement due to interruption or absence of the IVC. Azygous continuation of an anomalous IVC is seen in 0.6% of patients with congenital heart disease, and has been associated with the polysplenia/asplenia syndrome. Enlargement of the azygous/hemiazygous system is important to recognize, as it can be confused with paraspinal masses and lymphadenopathy.
Primary mediastinal abscesses are quite rare. The most common causes are associated with complications secondary to coronary artery bypass surgery. Complications secondary to esophageal perforation is the second most common cause, whether iatrogenic or related to Boerhaaves syndrome. The mediastinum can be secondarily affected from head and neck infection. In our case, given the patient's bacteremia, extension from the sternoclavicular joint was suspected. Histoplasmosis is a recognized cause of mediastinitis/pericarditis. Surgical/percutaneous drainage as well as parenteral antibiotic treatment is needed for these often life threatening infections.
References:
Breckinridge, JW and Kinlaw, WB. Azygous continuation of Inferior Vena Cava:
CT Appearance. JCAT.4:392-397.
Heitzman ER: The Mediastinum. St. Louis Mosby, 1977, pp 231-247.
Breatnach E, Nath, PH, Delany, DJ: The Role of CT in Acute and Subacute
Mediastinitis. Clin. Radiology 37:139-145, 1986.
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