Disclosure Superior vena cava (SVC) syndrome (SVCS) is a constellation of symptoms that result from obstruction of the SVC.
The SVC is formed in the upper middle part of the mediastinum by the junction of the brachiocephalic veins. It is 6-8 cm long and drains into the right atrium at approximately the level of the right mainstem bronchus. The azygous vein loops over the right mainstem bronchus and connects to the posterolateral wall of the SVC. The SVC lies in a relatively confined space and is surrounded by several lymph node groups that predispose it to compression, invasion, or involvement in inflammatory conditions. Obstruction of the SVC can be due to malignant or benign disease. In a modern series, malignancy is, by far, the most common etiology (Rosch, 1987; Chen, 1990). The most frequent malignancies are bronchogenic carcinoma (in order of decreasing frequency: small cell carcinoma, squamous cell carcinoma, adenocarcinoma, large cell carcinoma), followed by non-Hodgkin lymphoma. Many other malignancies have been reported as essentially any mediastinal mass may compress or invade the SVC. Benign causes include central venous catheters (increasing in frequency), pacemaker wires, fibrosing mediastinitis, thoracic aortic aneurysms, and a multitude of unusual causes.
The clinical presentation of SVCS depends primarily on the acuity of SVC obstruction. With slowly progressive obstruction of the SVC, adequate collateral drainage may develop, and patients may have no or only mild symptoms. In acute SVC obstruction, collateral pathways do not have time to develop, and patients are more symptomatic. The level of SVC obstruction relative to the insertion of the azygous vein is predictive of the patient's degree of symptoms. Obstruction of the SVC above the insertion of the azygous vein may cause fewer symptoms, as the azygous vein provides venous drainage for the head and upper extremities. If the level of obstruction is below the azygous vein then venous drainage occurs via collaterals to the inferior vena cava. The most common presenting symptoms include facial and neck swelling, bilateral upper extremity swelling, dyspnea, headache, and cough. Other less frequent symptoms are cyanosis, hemoptysis, dysphagia, chest pain, signs of increased intracranial pressure (ie, somnolence, dizziness, visual disturbances), and hoarseness. Patients may also have symptoms related to the underlying disease process. Physical examination may reveal plethora; tachypnea; and/or venous distension and edema of the head, neck, and upper extremities, with collateral vein development in the upper torso. Other physical findings may be present, depending on the etiology. For example, patients with an underlying malignancy may have signs of Horner syndrome and/or vocal cord paralysis. |
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The examination of a patient with suspected SVCS depends on the patient's prior medical history. All patients should undergo chest radiography and Doppler ultrasonographic evaluation of the central veins. If normal venous waveforms are seen in the brachiocephalic, subclavian, and internal jugular veins, the presence of a significant SVC stenosis is unlikely (Kinney, 1996; Nazarian, 1995; Patel, 1999). In patients with suspected malignancy, CT of the thorax should be performed (Schwartz, 1986). Magnetic resonance venography can also be used to image the central veins in patients with allergies to contrast material or renal failure (Finn, 1993). If the findings of noninvasive imaging studies or if the clinical diagnosis of SVCS is uncertain, catheter venography and pressure measurements are extremely useful. The presence or absence of venous thrombosis must be determined. An acute onset or a change in symptoms suggests acute thrombosis. Ultrasonography is useful for excluding thrombus in the upper extremity, axillary, subclavian, and brachiocephalic veins in most patients. The SVC cannot be directly imaged because of the lack of an adequate acoustic window. SVC patency can be indirectly determined with normal waveforms in the subclavian and brachiocephalic veins. Contrast-enhanced venography may be required to exclude central venous thrombosis in patients with suboptimal or inconclusive ultrasonographic findings. Transesophageal echocardiography can also be used to image the SVC and right atrium (Gilon, 1998). Patients with mediastinal masses may have significant airway compromise and care must be taken when using conscious sedation (Shamberger, 1995). Obtaining a tissue diagnosis is the first step in the treatment of patients with SVCS due to a mediastinal mass. The work up of patients will vary according to the patient's age, past medical history and other imaging findings. Mediastinal masses can be examined by means of percutaneously biopsy under CT, and occasionally, ultrasonographic guidance. In certain circumstances, mediastinoscopy is required. Large core samples are needed in patients with suspected lymphoma. Pleural effusions can be aspirated and sent for cytology.
The treatment of patients with SVCS is determined by the etiology of the obstruction. SVCS can be broadly divided into 2 categories: benign disease and malignant disease. Benign diseaseBenign obstruction of the SVC is most often iatrogenic and secondary to the use of central venous catheters, pacemaker wires, and long-term hemodialysis. In patients with this condition, chronic intimal injury leads to intimal hyperplasia and venous stenosis. If the onset of symptoms is rapid, acute venous thrombosis may be present. Treatment decisions are based on the severity of symptoms, the life expectancy of the patient, the long-term central venous access requirements, and the presence or absence of central venous thrombosis. Medical management In patients with mild symptoms and no long-term venous access requirements, conservative treatment (elevation of the upper body) may suffice and allow collateral veins to develop. All patients with thrombosis of the central veins must receive anticoagulation therapy to reduce the risk of pulmonary embolus (Prandoni, 1999). In patients with central venous stenosis and no evidence of thrombosis, anticoagulation may be used to prevent acute thrombosis of the underlying lesion (Yim, 2000) although this has not been proven. Endovascular treatment In patients with long-term access requirements (ie, hemodialysis, total parental nutrition), severe SVCS symptoms, or a poor response to conservative treatment should be directed to restoring patency of the SVC. In the setting of central venous thrombosis, catheter-directed thrombolysis should be performed prior to any other interventions. The SVC stenosis is treated with angioplasty and, possibly, stent placement. The use of primary stents in benign SVC stenosis is not entirely clear, because patients often have a long life expectancy, and the long-term patency of SVC stents has not been proven. SVC stenosis secondary to previous central venous catheterization or pacemaker wires may be treated with only angioplasty (Sherry, 1986; Capek, 1989; Sunder, 1992). However, high recurrence rates can be expected, and some authors have reported reasonable short and mid-term results in small case series with primary stent placement (Rosenblum, 1994; Hemphill, 1996). Stents can be safely placed in the presence pacemaker wires (Slonim, 2000). Central venous catheters can be removed or repositioned for SVC stent placement (Perno, 1999). SVC stenosis due to fibrosis (secondary to radiation therapy or fibrosing mediastinitis) likely requires stent placement because of venous recoil after angioplasty. SVCS caused by fibrosing mediastinitis can be successfully treated with stents (Smith, 1997; Dodds, 1994). In patients without central venous thrombosis, the role of anticoagulation is not clear. Some authors recommend that all patients with new stents should undergo anticoagulation while endothelialization takes place. As mentioned previously, all patients with central venous thrombosis should receive anticoagulants for 3-6 months because significant pulmonary emboli may result. Surgical management Surgical bypass of SVC obstruction is a more invasive means of treating patients with SVCS. Good long-term patency rates have been reported (Doty, 1999; Alimi, 1998). However, this procedure requires a high level of technical expertise, and it is extremely invasive. To the author's knowledge, no studies have been performed to compare surgery with SVC stent placement. The presence of an SVC stent does not preclude surgical bypass, and the conclusion that endovascular repair is preferred to a more invasive surgical procedure seems reasonable. Malignant diseasePatients with malignant obstruction of the SVC have a short life expectancy (<7 mo). The goal in treating these patients is to provide prompt and lasting relief of the SVCS symptoms. Long-term patency is usually not a consideration except in patients with potentially curable disease. Usually, the onset of SVCS is insidious, and the initial step in treating these patients is to obtain a tissue diagnosis so that appropriate radiation or chemotherapy can be started. Rarely, patients may have acute airway obstruction or cerebral edema that requires emergency treatment prior to a histologic diagnosis. Medical management Medical management is limited, but it can be used to treat patients with mild symptoms or to achieve short-term palliation. Treatment options include elevation of the upper body, the administration of supplemental oxygen and/or diuretics, and fluid restriction (Baker, 1992). Steroids may also be used, but their benefits are unproven. Radiation and chemotherapy The use radiation and/or chemotherapy are based on the histologic characteristics of the tumor. With both modalities, patients with SVCS have improved, with response rates greater than 70% (Armstrong, 1987; Urban, 1993; Wurschmidt, 1995). Chemotherapy alone will usually resolve the SVC obstruction from large mediastinal masses associated with leukemia or non-Hodgkin lymphoma in children and adolescents. Endovascular treatment Over the last 15 years, the use of angioplasty and stents in the treatment of malignant SVCS has flourished. Initially, SVC stents were used in patients in whom the condition fails to respond to traditional therapy or in whom symptoms recur after traditional therapy. In this patient population, SVC stents have had dramatic technical and clinical results, with symptom relief in more than 90% of the patients (Rosch, 1997; Watkinson, 1993; Dyet, 1993; Crowe, 1995; Tanigawa, 1998). Given the excellent results in this patient population, initially stent placement in all patients with malignant SVCS has been considered. To the author's knowledge, no prospective trials have been performed to compare radiation and chemotherapy with primary SVC stent placement. Findings from a large number of case series demonstrate excellent clinical results with SVC stents, with low complication rates. In 1 retrospective study in which radiation therapy and SVC stent use were compared, stent use offered several significant advantages, including faster relief of symptoms, greater improvement of symptoms, and a lower recurrence of symptoms (Nicholson, 1997). A strong argument can be made for primary SVC stent use in any patient with moderate or severe symptoms (Thony, 1999; Nicholson, 1997). Some patients with malignancy may have acute and severe SVCS and require urgent treatment. In this situation, the tissue diagnosis can be delayed, and endovascular treatment can be performed. Stent placement rapidly relieves the symptoms and does not affect the ability to make a tissue diagnosis at a later date. Radiation therapy and chemotherapy should not be started until tissue is obtained, and they often do not yield prompt symptomatic relief; in fact, they may cause transient worsening. Surgical treatment The results of surgical treatment of malignant SVCS were reported in a small group of patients prior to the availability of intravascular stents. The technical results were excellent (Doty, 1982); however, the utility of this procedure in this patient population is extremely limited when compared with that of newer endovascular options.
Indications and treatment options Endovascular treatment options in SVCS include thrombolysis, angioplasty, and stent placement. The approach must be individualized to each patient, with consideration to the etiology of the obstruction and the severity of the symptoms. Stents must be placed in malignant SVC obstructions of adult patients that need treatment to achieve any lasting effect. The use of primary stents in benign disease is not indicated in most patients. Recurrent SVC stenosis of occlusion is readily treatable with repeat endovascular intervention. Central venous catheters can be snared and repositioned to allow stent placement in an SVC stenosis. Contraindications Few absolute contraindications to the endovascular treatment of SVCS exist. The patient's condition must be stable enough for the patient to undergo a 1- to 3-hour procedure. Coagulopathies should be corrected. Appropriate caution must be taken when SVC stents are placed in patients with transvenous pacing leads (Slonin, 2000). Tumor invasion in the SVC, complete SVC occlusion, and/or extensive SVC thrombosis increases the technical skill required for completing the procedure, but are not contraindications. Thrombolytics and anticoagulants must be used cautiously in patients with a malignancy. Technique Venography of the central venous circulation is performed prior to stent placement. The easiest approach usually from a neck (internal jugular) or arm vein. Venography in 2 or more projections is required to demonstrate the extent of thrombus and the location, severity, and length of the obstruction. Evidence of tumor in growth should be determined. In patients SVCS caused by central venous catheters, thin webs may develop; these can be difficult to appreciate venographically. Pressure gradients should be assessed. Gradients greater than a few millimeters can be significant. Pressure measurements in patients with a dialysis fistula are more difficult to interpret. However, pull-back measurements should reveal focally significant lesions. Patients with SVC obstruction often have superimposed acute or subacute thrombus. Thrombolytic drugs have been extremely effective in the treatment of a clot, but the usual contraindications apply (Kee, 1998). In particular, care must be exercised in patients with malignant disease, and intracranial metastasis must be excluded. The thrombolytic drug is delivered directly into the thrombus by using infusion catheters. Multiple catheters and/or coaxial infusion systems can be used, depending on operator preference. The optimal thrombolytic agent and dose has not been determined for central venous thrombosis. Currently available drugs are urokinase (Abbott Laboratories), tPA (alteplase; Genentech, Inc) and RPA (reteplase [Retavase]; Centocor). Urokinase has been widely used and has recently been reintroduced for clinical use. Dosing is variable with ranges from 50,000 U/h to 250,000 U/h. Heparin is typically used with target activated partial thromboplastin time (aPTT) of 60-90 seconds. tPA doses can be based on the patient's weight (0.02-0.05 mg/kg/h) or on an absolute dose (0.5-2 mg/h). Low-dose heparin should also be given (ie, <500 U/h), but therapeutic levels of heparin should be avoided because of increased bleeding complications. The usual dose for RPA for venous thrombosis is 0.5 U/h with concomitant low-dose heparin. Further research and experience will provide better data about the selection of thrombolytic agent and the role of other drugs such as heparin and the glycoprotein IIB IIIA inhibitors. A variety of mechanical thrombectomy devices are available. However, only anecdotal reports about their use in the central venous circulation are available (Henry, 1998). The SVC obstruction must be crossed prior to angioplasty and/or stent placement. Often, the easiest approach is from above the lesion. Crossing an occluded SVC from below can be difficult, especially if the lesion extends to the right atrium. A through-and-through wire is often necessary in treating extremely tight stenoses (Clark, 2000). In most instances, sheaths of 8F or larger are required when large stents and balloons are used. Guiding catheters are extremely useful. Rarely, chronic occlusions may require the use of sharp techniques to reestablish patency (Farrell, 1999). Once the stenosis is crossed, the patient should receive heparin. Predilation is often required before the stent delivery system is positioned. Predilation also allows the operator to better appreciate the character of the stenosis. Extremely fibrotic lesions that have a tendency to cause stents to squirt out of position can be recognized, and appropriate measures (eg, use of a longer stent for more stability) can to taken to avoid this complication. In the literature, the most commonly used stents are Gianturco Z stents, Wallstents, and Palmaz stents, although a multitude of other stent designs have become available. Large stent diameters (>14 mm) are required unless kissing stents that extend into the brachiocephalic veins are used. In malignant lesions, stents should be a few centimeters longer than the lesion to provide for growth of the neoplasm. In benign lesions, the shortest possible stent should be used. Stents may be placed in a kissing fashion, with extension into the brachiocephalic veins. The Gianturco stent (Cook) has been widely used in treating malignant SVC obstruction, with excellent technical success and patency rates (Buscher, 2000; Kishi, 1993; Gaines, 1994; Rosch, 1992). The open design of the stent allows placement across inflowing veins with little concern, but this design also may also facilitate tumor ingrowth. Migration is a potential issue when a single body system is used. The stent is also rigid and can be difficult to place around bends. Use of this stent has decreased in recent years as newer products have become available. The Wallstent (Boston Scientific), a self-expanding stainless steel stent, is available in a wide variety of lengths and diameters. It has been extensively used in the central veins (Miller, 2000; Gross, 1997). The delivery system is 12F or smaller, even with large stent diameters. The stent has a tight weave that may limit tumor ingrowth. Disadvantages of this design are its low expansile force, significant foreshortening that makes accurate placement difficult, and the potential for migration if it is not well centered on the lesion. A covered version of this stent in now available (Wallgraft), and it may potentially limit tumor ingrowth. The advantages of the balloon-expandable Palmaz stent (Cordis Endovascular) include extremely accurate placement and the ability for staged dilation to larger diameters, which is a potential consideration in the pediatric population. The short lengths, the maximum diameter of about 14 mm, and the potential for compression limit the use of this stent. Many new stents have become available in recent years. However, little has been published about their use in the central veins. The Intrastent LD (ITI Therapeutics) is a balloon-expandable stent that is available in long lengths and that can be dilated to large diameters (18 mm) without significant shortening. The Smart stent (Cordis Endovascular), a self-expanding Nitinol stent, now comes in diameters as large as 14 mm; it seems to be less prone to migration, compared with the Wallstent. New covered stents (Wallgraft, Boston Scientific and Hemobahn, Gore) are available for clinical use. These likely will prove useful for malignant lesions by preventing tumor ingrowth. Their role in benign central venous stenosis and prevention of stent restenosis is unknown, as little published data about their use in the central venous circulation is available. After SVC stent insertion, most patients can be monitored on a regular nursing ward. However, closer observation should be considered in patients with multiple comorbidities (ie, limited cardiac reserve). Stent positioning should be documented with a chest radiograph. Doppler ultrasonography of the upper extremities should be performed before the patient is discharged home to document baseline venous waveforms. The role of anticoagulation is debated in the literature. In patients with central venous thrombosis, even after successful thrombolysis, short-term (3-6 mo) anticoagulation should be strongly considered. Some authors recommend long-term anticoagulation in this setting. Anticoagulation must be used with caution in patients with malignancy. In patients without SVC thrombus, anticoagulation is not likely to be necessary, although short-term treatment might be used until stent endothelialization has occurred. In terms of long-term follow-up, patients must be monitored for stent patency and positioning. Stent positioning is easily determined with chest radiography. Indirect SVC stent surveillance can be performed with Doppler ultrasonography of the upper extremity and neck veins. Follow-up schedules vary by physician. A reasonable schedule might include ultrasonography at 1, 3, and 6 months and yearly thereafter. Treatment is easier with recurrent central venous stenosis than with SVC thrombosis or occlusion. Close clinical and ultrasonographic follow-up is extremely important in maintaining stent patency. Treating a recurrent stenosis is always easier than treating stent occlusion or thrombosis.
Success rates Procedural success rates are high (80-100%), regardless of the stent used (Miller, 2000; Stock, 1995). In most patients, symptoms improve or completely resolve within 2-3 days. Often, patients have a dramatic improvement immediately after stent deployment. The life expectancy of patients with SVCS due to malignant disease is short, with 2-year survival rate of less than 5% in patients with bronchogenic carcinoma (Chen, 1990). After SVC stent placement, most patients are asymptomatic for the remainder of their lifetime. Recurrence of SVCS can be due to a combination of thrombosis, intimal hyperplasia, and tumor ingrowth or overgrowth of the stent. In most patients, repeat intervention is successful and results in symptom resolution. The results of only a small case series (with limited follow-up) of the use of SVC stents in benign disease have been reported. Two series, with a total of 18 patients, had 100% technical success, with complete resolution of SVCS symptoms. Over a follow-up period of 1-36 months, only 1 recurrence was detected; this was successfully treated with repeat stent placement. Complications Complications from SVC angioplasty and stent placement are unusual. Stent migration can occur and may necessitate stent retrieval and/or repeat stent placement. Stent migration to the heart may result in death. The increased venous return to the right side of the heart can cause pulmonary edema. One death from cor pulmonale has been reported. Stent thrombosis may occur, particularly in patients who initially had SVC thrombosis. The use of thrombolytics increases the complication rate to as high as 10%, secondary to bleeding problems.
The primary consideration in patients with SVCS is determining the underlying etiology of the obstruction. In the last 2 decades, improvements in catheter-based technologies have provided a minimally invasive technique for restoring flow in the SVC, with dramatic resolution of SVCS symptoms. SVC stent placement should be considered in any patient with malignant disease and moderate-to-severe SVCS symptoms. Primary SVC stent placement in benign disease is less well defined because long-term patency rates are unknown.
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