What is superior vena cava

Superior vena cava is formed by the junction of the left and right innominate (brachiocephalic) veins and its function is to return deoxygenated blood from the head, neck, upper extremities and torso back to the right atrium of the heart. Blood coming from body regions superior to the diaphragm (excluding the heart wall) enters the right atrium via the superior vena cava. The superior vena cava is a large-diameter (24 mm), yet short, vein that receives venous return from the upper half of the body, above the diaphragm. Venous return from the lower half, below the diaphragm, flows through the inferior vena cava. The superior vena cava is located in the anterior right superior mediastinum. It is the typical site of central venous access via a central venous catheter or a peripherally inserted central catheter.

Figure 1. Superior vena cava

Superior vena cava anatomy

Superior vena cava is formed by the left and right brachiocephalic veins (also referred to as the innominate veins), which also receive blood from the upper limbs, eyes and neck, behind the lower border of the first right costal cartilage. Superior vena cava passes vertically downwards behind first intercostal space and receives azygos vein just before it pierces the fibrous pericardium opposite right second costal cartilage and its lower part is intrapericardial. And then, it ends in the upper and posterior part of the sinus venarum of the right atrium, at the upper right front portion of the heart.

No valve divides the superior vena cava from the right atrium. As a result, the (right) atrial and (right) ventricular contractions are conducted up into the internal jugular vein and, through the sternocleidomastoid muscle, can be seen as the jugular venous pressure.

Figure 2. Superior vena cava anatomy

Persistent left superior vena cava

In persistent left superior vena cava, the left brachiocephalic vein does not develop fully and the left upper limb and head & neck drain into the right atrium via the coronary sinus. Persistent left superior vena cava is the most common variation of the thoracic venous system, is prevalent in 0.3% of the population and an embryologic remnant that results from a failure to involute.

The persistent left superior vena cava variation, in isolation, is considered benign, but is very frequently associated with cardiac abnormalities (e.g. ventricular septal defect, atrioventricular septal defect) that have a significant mortality and morbidity. Persistent left superior vena cava is more frequent in patients with congenital heart defects.

What does the superior vena cava do?

Superior vena cava function is to return deoxygenated blood from the head, neck, upper extremities and torso back to the right atrium of the heart.

Superior vena cava syndrome

Superior vena cava syndrome is a collection of clinical signs and symptoms resulting from either partial or complete obstruction of blood flow through the superior vena cava ¹. The superior vena cava syndrome is a medical emergency and is most often due to a malignant process in the chest. Once diagnosed, the condition needs to be treated. Otherwise, it can lead to brain and upper airway edema. Since the superior vena cava traverses the superior mediastinum, it can be obstructed from any number of causes. Superior vena cava obstruction is most commonly a result of thrombus formation or tumor infiltration of the superior vena cava wall. Today, superior vena cava syndrome is most commonly seen secondary to malignancy although there has been a more recent rise in benign causes ¹. The resulting venous congestion produces a clinical scenario relating to increased upper body venous pressures. The most common signs and symptoms include face or neck swelling, upper extremity swelling, dyspnea (shortness of breath), cough, and dilated chest vein collaterals ².

While lung cancer is the most common cause of superior vena cava syndrome, other causes include aortic aneurysms, mediastinal fibrosis, pericarditis, thrombosis as a result of venous catheters and infections like histoplasmosis ³. Superior vena cava syndrome is often seen in middle-aged individuals. Radiotherapy is often used as the initial treatment when the diagnosis is uncertain. In the past surgery was done to reconstruct the superior vena cava but today percutaneous angioplasty and stenting offer a better option. With stenting, symptomatic relief is obtained within 24 to 48 hours ⁴.

An estimated 15,000 cases of superior vena cava syndrome occur each year in the United States, with studies pointing to increasing frequency due to the concomitant rise in the use of semipermanent intravascular catheters ¹. The incidence of superior vena cava syndrome reported in the literature range from 1 in 650 to 1 in 3100 patients ¹.

The goal of superior vena cava syndrome treatment is to relieve the blockage. Diuretics (water pills) or steroids (anti-inflammtory drugs) may be used to temporarily relieve swelling. Other treatment options may include radiation or chemotherapy to shrink the tumor, or surgery to remove the tumors. Surgery to bypass the obstruction is rarely performed. Placement of a stent (tube placed inside a blood vessel) to open up the superior vena cava may be performed.

Figure 3. Superior vena cava syndrome

Superior vena cava syndrome causes

Today, the majority of superior vena cava syndromes are the result of mediastinal malignancies, primary among which is small cell bronchogenic carcinoma ¹. The second most commonly associated malignancy is non-Hodgkins lymphoma, followed by metastatic tumors. In addition, benign or nonmalignant causes of superior vena cava syndrome now comprise at least 40% of cases. Iatrogenic thrombus formation or superior vena cava stenosis is a growing cause due to pacemaker wires and semipermanent intravascular catheters used for hemodialysis, long term antibiotics, or chemotherapy ⁵.

Other types of cancer that can lead to superior vena cava syndrome include:

• Breast cancer
• Lymphoma
• Metastatic lung cancer (lung cancer that spreads)
• Testicular cancer
• Thyroid cancer
• Thymus tumor

Superior vena cava obstruction can also be caused by noncancerous conditions that cause scarring. These conditions include:

• Histoplasmosis (a type of fungal infection)
• Inflammation of a vein (thrombophlebitis)
• Lung infections (such as tuberculosis)

Other causes of superior vena cava obstruction include:

• Aortic aneurysm (a widening of the artery that leaves the heart)
• Blood clots in the superior vena cava
• Constrictive pericarditis (tightening of the thin lining of the heart)
• Effects of radiation therapy for certain medical conditions
• Enlargement of the thyroid gland (goiter)

Catheters placed in the large veins of the upper arm and neck may cause blood clots in the superior vena cava.

The superior vena cava is part of the low-pressure venous system containing thin walls susceptible to damage by a variety of pathologic mechanisms. These mechanisms can be divided into three categories which are compromised vessel anatomy, impaired venous flow, and diminished vessel wall integrity. These mechanisms often coexist in patients presenting with superior vena cava syndrome. Extrinsic compression and obstruction of the superior vena cava by a mass in the mediastinum is the most common cause of superior vena cava syndrome. Most often this is associated with malignancy, however there are a variety of nonmalignant masses as well as dilation of the overlying aorta that can cause compression. A growing proportion of superior vena cava syndromes are now associated with occlusive venous thrombus formation that compromises venous flow back to the heart. The increasing use of indwelling intravascular devices such as catheters as well as pacemakers and implantable cardioverter defibrillator (ICD) leads have played a major role in this growth. Resultant venous wall inflammation, fibrosis, and eventual thrombus leads to stenosis of the vessel itself ⁶.

Superior vena cava syndrome symptoms

Symptoms occur when something blocks the superior vena cava blood flowing back to the heart. Superior vena cava syndrome symptoms may begin suddenly or gradually, and may worsen when you bend over or lie down.

Early signs of superior vena cava syndrome include:

• Swelling around the eye
• Swelling of the face
• Swelling of the whites of the eyes

The swelling will most likely be worse in the early morning hours and go away by mid-morning.

The most common superior vena cava syndrome symptoms are shortness of breath (dyspnea) and swelling of the face, neck, trunk, and arms.

Other possible superior vena cava syndrome symptoms include:

• Decreased alertness
• Dizziness, fainting
• Headache
• Reddish face or cheeks
• Reddish palms
• Reddish mucous membranes (inside the nose, mouth, and other places)
• Redness changing to blueness later
• Sensation of head or ear fullness
• Vision changes

Superior vena cava syndrome possible complications

The throat could become blocked, which can block the airways.

Increased pressure may develop in the brain, leading to changed levels of consciousness, nausea, vomiting, or vision changes.

Superior vena cava syndrome diagnosis

The diagnosis of superior vena cava syndrome is made largely based on a patient’s history and physical findings, which often develop over a period of days to weeks. This insidious onset is a result of a collateral vascular network that exists to divert blood to the lower body where it is then returned to the heart through the inferior vena cava, azygous vein, and the intercostals. The clinical findings in superior vena cava syndrome are closely linked to venous congestion and the resultant elevation in venous pressures seen in the upper body. A careful physical examination is often sufficient to rule out a cardiogenic origin to the patient’s symptoms. The most common presenting symptoms of superior vena cava syndrome are face/neck swelling, distended neck veins, cough, dyspnea, orthopnea, upper extremity swelling, distended chest vein collaterals, and conjunctival suffusion. Other less common symptoms of superior vena cava syndrome include stridor, hoarseness, dysphagia, pleural effusion, head plethora, headache, nausea, lightheadedness, syncope, change in vision, altered mental status, upper body edema, cyanosis, papilledema, stupor, and coma. Some rare but serious clinical consequences reported in superior vena cava syndrome include cerebral edema and upper respiratory compromise secondary to edema of larynx and pharynx.

Investigation

Patients with high clinical suspicion for superior vena cava syndrome should undergo imaging of the upper body and vasculature. Ultrasound of the jugular, subclavian, and innominate veins can help to identify a thrombus within the vessel lumen. Radiographic imaging and MRI also play a critical role providing additional information as to the location, severity, and etiology of the superior vena cava obstruction. CT of the chest with the presence of collateral vessels is associated with a diagnostic sensitivity of 96% and a specificity of 92%. Venography is widely accepted as the gold standard for visualizing and diagnosing a venous obstruction. This modality should be used concomitantly with endovascular intervention for patients with a severe presentation of superior vena cava syndrome ⁷.

If lung cancer is suspected, a bronchoscopy may be done. During this procedure, a scope is used to view inside the airways and lungs.

Superior vena cava syndrome treatment

Following a clinical diagnosis, supportive therapy and medical management is commonly initiated. This involves elevation of the patient’s head as a simple maneuver with the goal of decreasing venous pressure. Further management is guided by the patient’s underlying superior vena cava syndrome cause. For patients with thrombus related to an indwelling intravascular device, removal should be considered along with anticoagulation therapy and catheter directed thrombolysis. Multidisciplinary treatment planning for those with obstruction due to malignancy is important as tumor type and staging can help to guide appropriate chemotherapy or radiation therapy. Open surgical repair through bypass grafting with spiral saphenous vein, femoral vein, polytetrafluoroethylene graft, or Dacron graft have traditionally been considered to overcome superior vena cava obstruction. However, this is now reserved for cases in which recanalization through endovascular repair is either not possible or has previously failed. With expanding treatment options for both benign and malignant etiology, endovascular therapy is now widely considered as the first-line treatment for superior vena cava syndrome. Less invasive endovascular management can offer patients immediate relief of symptoms. Acute or subacute thrombus can be managed with catheter based thrombolysis or thrombectomy prior to venoplasty and stent placement ⁸.

Superior vena cava syndrome prognosis

The outcome of superior vena cava syndrome varies, depending on the cause and the amount of blockage.

Superior vena cava obstruction caused by a tumor is a sign that the tumor has spread, and it indicates a poorer long-term outlook.

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