Superior vena cava obstruction

Superior vena cava (SVC) obstruction, also known as SVC syndrome (SVCS) is a condition caused by obstruction of the SVC’s venous return from the head, neck upper limbs and superior thorax. The obstruction may be an intraluminal obstruction or it may be due to external compression. It is most commonly a complication of malignancies but may be due to thrombosis in patients with central venous catheters or pacemakers. Early recognition and management is vital to avoid severe airway compromise, haemodynamic instability and cerebral oedema.

🦴 Anatomy

• Superior vena cava

The SVC is a large, thin walled, major venous structure that drains blood from the head neck, upper limb and upper thorax. It descends through the mediastinum and as such is subject to compression by mediastinal tumours.

It is formed by the union of the right and left brachiocephalic veins. It descends behind the costal cartilages before ending up at the right atrium of the heart around the level of the third intercostal space (adjacent to the aorta and trachea).

The azygous vein joins the SVC just prior to entering the right atrium. This acts as a major collateral pathway in cases of SVC obstruction.

• Brachiocephalic veins

Formed by the union of the internal jugular vein and subclavian veins. The right brachiocephalic has a short and vertical course while the left has a longer course that crosses the midline (making it more susceptible to compression by masses of the mediastinum.

It is important to consider the level of the obstruction in relation to the brachiocephalics as an obstruction above may lead to facial and neck swelling while an obstruction below may allow for collateral circulation via the azygous system.

• Azygous vein

The azygous vein drains the thoracic wall and upper lumbar region (via intercostal and lumbar veins). It then travels over the right main bronchus before draining into the SVC. It connects with the hemiazygous and accessory hemiazygous veins on the left hand side.

As mentioned it is a major collateral pathway to direct blood from the SVC regions into the inferior vena cava (IVC) regions.

• Internal jugular veins

These are a pair of veins that drain the brain, neck, and face into the brachiocephalic veins. It is important to recognise distension of the jugular vein as a hallmark sign of SVC syndrome.

• Internal mammary veins

They are a pair of veins that run parallel to the sternum and drain into the brachiocephalic veins. They collect blood from the anterior thorax and breast.

They serve as an important collateral to allow blood to flow into the inferior epigastric veins and then the IVC. If they become obstructed it may lead to dilated chest wall veins which can be seen on examination.

• Lateral thoracic veins

The lateral thoracic veins run lateral to the thoracic well and then connect to the axillary vein (which connects to the subclavian and brachiocephalic veins).

It forms an important collateral route via the thoracoepigastric vein to allow blood flow into the IVC. If obstructed it may lead to prominent veins on the lateral chest and abdomen.

• Vertebral venous plexus

These are an extensive network of valveless veins around the vertebral column. It connects with the dural venous sinuses, azygous system and lumbar veins to act as a low-resistant collateral system. It may add to brain oedema in severe obstruction, however. If obstructed it may lead to increased intracranial pressure, headaches, confusion.

Pathophysiology

SVC syndrome is predominantly caused by malignancy but there are non-malignant causes to discuss that happen in around 20% of cases.

• Malignant causes
• Lung cancer - this is the most common cause, making up around 70% of cases. Most are non-small-cell lung cancer, but a higher proportion of patients with small-cell lung cancer develop SVC syndrome (around 10-20%). Small-cell lung cancer is the biggest risk factor for SVC syndrome.
• Lymphoma - most commonly diffuse large B-cell lymphoma and sometimes lymphoblastic lymphoma. Hodgkin’s lymphoma often has mediastinal involvement but SVC syndrome with Hodgkin’s lymphoma is rare. Non-Hodgkin’s lymphoma is the most common cause in children.
• Metastatic cancer - most commonly from breast cancers, but it may also include colorectal cancers, oesophageal cancers, Kaposi’s sarcoma and fibrous mesothelioma.
• Non-malignant causes
• Intravascular devices - such as pacemakers, central catheters, cardiac resynchronisation therapy and implantable cardiac defibrillators. It will lead to a thrombosis in the SVC which causes the obstruction. It may also occur in hypercoagulable states such as antiphospholipid syndrome.
• Mediastinal fibrosis - due to radiotherapy, tuberculosis and histoplasmosis.
• Collagen-vascular diseases - such as sarcoidosis and Behçet’s syndrome.
• Aortic aneurysm

😷 Presentation

In its initial stages the disease is asymptomatic as blood is diverted through the collateral systems sufficiently.

Symptoms may include:

• Facial and neck swelling - worse in the morning or when bending forward.
• Facial plethora
• Dyspnoea - this is the most common symptom
• Cough
• Hoarseness of voice - due to the laryngeal oedema.
• Dysphagia
• Arm swelling
• Chest pain - often due to the encroachment of the tumour into surrounding tissues.
• Stridor - suggests airway compromise and needs emergency attention.
• Syncope
• Raised intracranial pressure
• Headaches
• Blurred vision
• Dizziness

Some physical examination findings:

• Jugular venous distension - that is non-pulsatile (as it is not related to cardiac failure).
• Prominent chest wall collateral veins
• Pemberton’s sign - lifting the arms over the head for >1 minute leads to facial plethora.

Since malignancy is the leading cause of SVC syndrome there often are signs and symptoms relating to this (such as weight loss, cachexia, anorexia, nausea and vomiting, haemoptysis).

🔍 Investigations

The diagnosis of SVC syndrome can be made clinically based on history and examination findings. However, as the syndrome is related to the underlying cause we have to investigate this further:

• 🥇 Chest X-ray - it may reveal a widened mediastinum or right-sided mass.
• 🏆 Contrast-enhanced CT/MRI
• Biopsy - for histopathological diagnosis.
• Upper extremity duplex ultrasound - if there is the suspicion of a thrombosis in the peripheral veins.
• Venography - to visualise the venous system. It can be done to assess the severity but also to aid visualisation for stenting.

🧰 Management

🚨 Complications

• Laryngeal oedema - leading to stridor and airway compromise.
• Cerebral oedema - leading to altered consciousness and seizures.
• Decreased cardiac output
• Pulmonary embolism - when an associated thrombus is present.