Any pathologic process that invades the lymphatics or structures of the superior mediastinum can encroach on the thin-walled, compliant SVC and cause obstruction of venous return to the heart. SVCS may result from external compression, direct invasion, or thrombosis of the SVC. The most common cause of SVC obstruction is malignant disease, usually lung cancer, particularly small cell lung cancer (SCLC), lymphoma, and metastatic breast cancer.¹ Furthermore, 80% of the tumors inducing SVCS originate in the right lung.¹ The most common nonmalignant cause of SVCS is thrombosis of the SVC associated with indwelling central venous catheters or pacemakers.²

Clinical Presentation and Physical Examination

SVCS is usually insidious in onset. The severity of presentation depends on the underlying cause, rapidity of obstruction, concurrent thrombosis, location of obstruction, and adequacy of collateral circulation. Swelling of the face, neck, or chest or orthopnea is the classic presenting complaint.² Other symptoms include headache, dizziness, visual disturbances, hoarseness, chest pain, and dysphagia. Physical findings include venous distention in the upper body, facial edema, cyanosis, arm and hand edema, telangiectasias of the chest and upper back, tachypnea, hoarseness, and stridor.^1,2 Neurologic abnormalities resulting from increased intracranial pressure include papilledema, agitation, lethargy, confusion, seizures, and coma.

Diagnostics

A chest x-ray examination commonly reflects a superior mediastinal mass or widening (64%), pleural effusion (26%), right hilar mass (12%), or adenopathy; however, 16% of patients may have normal radiographic findings.¹ Magnetic resonance imaging (MRI) or computed tomography (CT) scan of the chest is indicated to localize the level of SVC obstruction and to identify the presence of intrinsic or extrinsic obstruction, superimposed thrombosis, collateral circulation, mediastinal adenopathy, masses, and other sites of unrecognized disease in the chest. Because the underlying pathologic condition in many patients with new-onset SVCS is not identified, other diagnostic evaluations (biopsies) are almost always required before the definitive therapy can be administered.

With SVCS, idiopathic mediastinal fibrosis, tuberculosis, histoplasmosis, syphilis, and aneurysm of the aortic arch are among the differential diagnoses.^1,3 Other diagnoses to consider are constrictive pericarditis and thrombosis from indwelling catheters or pacemaker leads.

Treatment is directed at the underlying cause. The treatment of SVCS should be guided by the stage and histologic features of the primary process. Chemotherapy alone or in combination with radiotherapy is the treatment of choice for SVCS caused by SCLC and non-Hodgkin lymphoma, whereas non-SCLC is best treated with radiotherapy, endovascular stent placement, or both.^1,2,4 Temporary measures to alleviate discomfort include bed rest with elevation of the upper body, supplemental oxygen, and limited intravenous fluids. Venipuncture and intravenous lines should not be placed in the upper extremities. There may be temporary symptomatic improvement with diuretic therapy and reduced sodium diets, but dehydration may increase the risk for thrombosis and exacerbate the SVCS. The use of short-term corticosteroids to reduce the inflammation and edema associated with the tumor is controversial; however, corticosteroids and bronchodilators are indicated if stridor or airway compromise is present. Intubation or an emergency tracheostomy may be necessary. Patients with central nervous system (CNS) signs require high doses of dexamethasone to relieve increased intracranial pressure.¹ If the SVCS is a result of thrombosis, thrombolytic agents (urokinase or streptokinase) are effective if they are initiated within 7 days of symptom onset. Other, less-commonly used treatments include balloon angioplasty, caval stenting, and surgical bypass.² If left untreated, patients will develop marked venous distention, laryngeal edema, stridor, increased intracranial pressure, sagittal sinus thrombosis, and cerebral edema.

Pathophysiology

SCC usually results when metastasis from a vertebral body extends into the epidural space or when a vertebral body collapses, resulting in a compression fracture. Direct extension of a paraspinous tumor through a vertebral foramen will also compress the spinal cord.⁶ Rarely, a tumor may emanate from the epidural space without any bone involvement. The compression of the spinal cord impairs blood flow, resulting in spinal cord edema, ischemia, and infarction. The incidence of SCC is highest in multiple myeloma (8%), prostate cancer (7%), nasopharyngeal cancer (6.5%), and breast cancer (5.5%).⁶

Clinical Presentation and Physical Examination

The signs and symptoms of SCC depend on the area of spinal cord involved. The thoracic spine is involved most often (70%), followed by the lumbosacral (20%) and cervical (10%) vertebrae.² In 70% to 95% of patients, the presenting symptom is a constant, dull, aching back pain that is often worse when the patient is supine (opposite of the usual finding with a herniated disk).^6,8 The pain, which antedates the diagnosis of SCC by days to many months, is exacerbated by movement, sneezing, straining, or neck flexion.^5,6,8 Weakness, especially of the lower extremities, is the second most common symptom. It may be preceded or accompanied by sensory loss or paresthesia that ascends to the level of compression.² The loss of proprioception produces ataxia. Autonomic dysfunctions, such as urinary frequency, urgency, urinary retention, constipation, and sexual impotence, are late manifestations and are associated with a poor prognosis.⁶ Physical findings may include tenderness on palpation of the involved vertebrae, hyperactive deep tendon reflexes, extensor plantar response, palpable bladder, and diminished rectal tone.²

Diagnostics

After an accurate neurologic history and physical examination, MRI is the preferred diagnostic test for SCC; MRI has a sensitivity of 93% and a specificity of 97%. A CT scan or myelography is reserved for patients who cannot undergo MRI (e.g., patients who have cardiac pacemakers or are claustrophobic).⁶ Tumor biopsy may also be used to diagnose cancer in patients not previously diagnosed.⁹ Patients with cancer who are seen with a new complaint of back pain should undergo an evaluation for SCC.

Clear indications of SCC in the cancer patient (e.g., focal weakness, ataxia, bowel or bladder dysfunction accompanied by back pain) demand an emergent evaluation and a referral. Immediate therapy with steroids (dexamethasone is most commonly used) may reduce vasogenic edema. The optimum loading dose and maintenance dose are controversial. An intravenous loading dose of 10 to 100 mg is given, followed by 4 to 24 mg every 6 hours. After 2 days, therapy is switched to 4 to 8 mg oral dexamethasone every 6 hours. Steroid doses are tapered every 4 days.^6,8 If neurologic decline results from dose reduction, the dose is maintained at effective levels during definitive treatment.

The decision to proceed with surgery, radiotherapy, or chemotherapy is based on the type of cancer. Radiotherapy alone is the definitive treatment for most patients.^2,5,6,8 Surgical decompression is indicated in the following situations: the histopathology of the cancer is unknown, neurologic deterioration develops during or after radiotherapy, the cancer is radiation resistant, a pathologic fracture causes compression by bone, or the spine is unstable.^2,5,6,8 Chemotherapy can be used for chemosensitive tumors (e.g., lung cancer, lymphoma) and is usually an adjunct to radiotherapy.^2,6