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Findings: Contrast venography during attempted Permacath insertion into right internal jugular vein showing almost complete occlusion of SVC with little amount of contrast flowing into right atrium and no contrast filling right atrium via IVC. A dilated hemiazygos vein is seen draining into the SVC.

Diagnosis: Thrombosed SVC and interrupted IVC with hemiazygos continuation.

Discussion: The hemiazygos vein typically arises from the left renal vein at L1 or L2 and travels anterior to the spine slightly left of the midline. At T12, it is joined by the left subcostal and ascending lumbar veins, and at T8, it passes posterior to the aorta, esophagus and thoracic duct, crossing the midline to join the azygos vein and eventually drain into the SVC. It receives the inferior esophageal and several small mediastinal veins as well as the left 8th and 12th posterior intercostal veins.

In this case, the lack of collateral development from the IVC to the SVC and the presence of a dilated hemiazygos vein suggest that the upper IVC obstruction is a congenital lesion. The hemiazygos does not cross the midline until well above the T8 level and enters the SVC at the typical location for the azygos to join it. Its anomalous route represents the chief conduit for the lower body's venous return, but this patient's venous drainage is compromised secondary to not only the absence of the IVC's connection to the right atrium, but also because of minimal drainage through the thrombosed SVC. This thrombus is likely a complication from repeated introduction of dialysis catheters and represents a surgical emergency. There are potentially several different interventions including sequential balloon dilatation and placement of intravascular stents. Another newer treatment involves a Goretex graft from the vein to the right atrial appendage to bypass the obstruction.

When the partial or complete IVC obstruction is acquired, the upper portion is least frequently involved and consequently has not been well studied. Potentially, collateral circulation can develop between the IVC and SVC, or if there is reversal of blood flow into hepatic vein and portal circulation, collaterals from the portal vein to the SVC or parieto-portal systemic collaterals (vertebral and deep ascending lumbar plexuses) may form. These channels may form: centrally via the ascending lumbar and intervertebral veins and azygos system; superficially via the inferior epigastric vein to the internal mammary and subclavian veins or via the circumflex iliac vein to the lateral thoracic and axillary veins; or rarely, via the pelvic plexus to the gonadal veins and renal-azygos system.

References:
Baum S. Abram's Angiography. Volume 1. 4th Edition.
Little, Brown, and Co., Boston; 1997:949-958.

Kadir S. Atlas of Normal and Variant Angiographic Anatomy
W. B. Saunders Co., Philadelphia; 1991:164-165.

El-Sabrout RA and Duncan JM. Right atrial bypass grafting for
Central Venous Obstruction Associated with Dialysis Access.
J Vasc Surg 1999;29(3):472-478.

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