By Dr Deepu
Definition
History
Pathophysiology
Presentation and Findings
Causes
Diagnostic Workup
Management
Pathophysiology:
History
Pathophysiology
Presentation and Findings
Causes
Diagnostic Workup
Management
Pathophysiology:
The SVC is the major drainage vessel for venous blood
from the head, neck, upper extremities, and upper thorax. It is a thin-walled,
low-pressure, vascular structure. This wall is easily compressed as it
traverses the right side of the mediastinum.
It is located in
the middle mediastinum and is surrounded by relatively rigid structures such as
the sternum, trachea, right bronchus, aorta, pulmonary artery, and the
perihilar and paratracheal lymph nodes. It extends from the junction of the
right and left innominate veins to the right atrium, a distance of 6-8 cm.
Obstruction of the SVC may be caused by neoplastic
invasion of the venous wall associated with intravascular thrombosis or, more
simply, by extrinsic pressure of a tumor mass against the relatively
thin-walled SVC. Complete SVC obstruction is the result of intravascular
thrombosis in combination with extrinsic pressure. Incomplete SVC obstruction
is more often secondary to extrinsic pressure without thrombosis. Other causes
include compression by intravascular arterial devices.
The incidence is on the rise, in line with the increased
use of endovascular devices.
An obstructed SVC initiates collateral venous return to
the heart from the upper half of the body through four principal pathways. The
first and most important pathway is the azygous venous system, which includes
the azygos vein, the hemiazygos vein, and the connecting intercostal veins. The
second pathway is the internal mammary venous system plus tributaries and
secondary communications to the superior and inferior epigastric veins. The
long thoracic venous system, with its connections to the femoral veins and
vertebral veins, provides the third and fourth collateral routes, respectively.
Despite these collateral pathways, venous pressure is
almost always elevated in the upper compartment if obstruction of the SVC is
present. Venous pressure as high as 200-500 cm H2 O has been recorded in patients with
severe SVCS.
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