The Human Circulatory System

Superior vena cava Obstruction

Superior vena cava Obstruction

Partial or complete obstruction of the superior vena cava is a relatively rare condition that is usually secondary to neo­plastic or inflammatory processes in the superior mediasti­num. The most frequent causes are (1) neoplasms, such as lymphomas, primary malignant mediastinal tumors, or carcinoma of the lung with direct extension (over 80%); (2) chronic fibrotic mediastinitis, either of unknown origin or secondary to tuberculosis, histoplasmosis, pyogenic infec­tions, or drugs, especially methysergide; (3) DVT, often by extension of the process from the axillary or subclavian vein into the innominate vein and vena cava associated with catheterization of these veins for dialysis or for hyper­alimentation; (4) aneurysm of the aortic arch; and (5) constrictive pericarditis.

Signs and symptoms

The onset of symptoms is acute or subacute. Symptoms include swelling of the neck and face and upper extremi­ties.

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Symptoms are often perceived as congestion and pres­ent as headache, dizziness, visual disturbances, stupor, syncope, or cough. T

here is progressive obstruction of the venous drainage of the head, neck, and upper extremities.

The cutaneous veins of the upper chest and lower neck become dilated, and flushing of the face and neck develops.

Brawny edema of the face, neck, and arms occurs later, and cyanosis of these areas then appears.

Cerebral and laryn­geal edema ultimately result in impaired function of the brain as well as respiratory insufficiency.

Bending over or lying down accentuates the symptoms; sitting quietly is generally preferred. The manifestations are more severe if the obstruction develops rapidly and if the azygos junction or the vena cava between that vein and the heart is obstructed.

Diagnosis

The venous pressure is elevated (often more than 20 cm of water) in the arm and is normal in the leg. Since lung can­cer is a common cause, bronchoscopy is often performed; transbronchial biopsy, however, is relatively contraindi­cated because of venous hypertension and the risk of bleeding.

Chest radiographs and a CT scan will define the location and often the nature of the obstructive process, and con­trast venography or magnetic resonance venography (MRV) will map out the extent and degree of the venous obstruction and the collateral circulation. Brachial venog­raphy or radionuclide scanning following intravenous injection of technetium (Tc-99m) pertechnetate demon­strates a block to the flow of contrast material into the right heart and enlarged collateral veins. These techniques also allow estimation of blood flow around the occlusion as well as serial evaluation of the response to therapy.

Treatment

Conservative measures, such as elevation of the head of the bed and lifestyle modification to avoid bending over, are useful. Balloon angioplasty of the obstructed caval segment combined with stent placement provides prompt relief of symptoms and is the procedure of choice for all etiologies. Occasionally, anticoagulation is needed, while thromboly­sis is rarely needed.

Urgent treatment for neoplasm consists of (1) cau­tious use of intravenous diuretics and (2) mediastinal irradiation, starting within 24 hours, with a treatment plan designed to give a high daily dose but a short total course of therapy to rapidly shrink the local tumor. Intensive combined therapy will palliate the process in up to 90% of patients. In patients with a subacute presenta­tion, radiation therapy alone usually suffices. Chemo­therapy is added if lymphoma or small-cell carcinoma is diagnosed.

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Long-term outcome is complicated by risk of re-occlusion from either thrombosis or further growth of the neoplasm. Surgical procedures to bypass the obstruc­tion are complicated by bleeding relating to high venous pressure. In cases where the thrombosis is secondary to an indwelling catheter, thrombolysis may be attempted. Clini­cal judgment is required since a long-standing clot may be fibrotic and the risk of bleeding will outweigh the potential benefit.

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