Radiation Oncology: A Question-Based Review

Superior Vena Cava Syndrome

Bronwyn R. Stall and Brent A. Tinnel

image Background

What vessels form the SVC?

The right and left brachiocephalic veins join to form the SVC.

What vessels form the brachiocephalic vein?

The internal jugular and subclavian veins join to form the brachiocephalic vein.

What is SVC syndrome?

SVC syndrome is extrinsic or intrinsic obstruction of blood flow through the SVC leading to proximal congestion.

At what bony landmark does the SVC begin?

The SVC begins at the level of the sternal angle.

Describe the course of the SVC.

The SVC begins at the sternal angle, extends inferiorly along the right lat side of the ascending aorta, and inserts into the right atrium.

What predisposes the SVC to compression?

The SVC is a thin-walled vessel with relatively low intravascular pressure and is therefore susceptible to compression by surrounding rigid structures including enlarged LNs and the trachea, sternum, pulmonary artery, and right mainstem bronchus.

What vessels form the collateral system of the SVC?

The collateral system of SVC is formed by the azygous, mammary, vertebral, lat thoracic, paraspinous, and esophageal vessels.

What vessels join to form the azygous vein?

The right subcostal and right ascending lumbar veins coalesce to form the azygous vein.

What is the most common cause of SVC syndrome?

Malignancy is the most common cause of SVC −syndrome.

Name 4 benign causes of SVC syndrome.

Benign causes of SVC syndrome:

1.     Catheter-induced thrombosis

2.     Chronic mediastinitis

3.     Retrosternal goiter

4.     CHF

Name 6 cancers associated with SVC syndrome.

Cancers associated with SVC syndrome:

1.     Non–small cell lung cancer (NSCLC)

2.     Small cell lung cancer (SCLC)

3.     Non-Hodgkin lymphoma (NHL)

4.     Thymoma

5.     Primary mediastinal germ cell tumors

6.     Mesothelioma

What is the most common malignant cause of SVC syndrome?

The most common malignant cause of SVC syndrome is NSCLC.

Are NSCLC or SCLC pts more likely to develop SVC syndrome?

SCLC pts are more likely to develop SVC syndrome than NSCLC pts b/c of their propensity toward rapid growth in central airways.

What is the most common cause of SVC syndrome in pts <50 yo?

In pts <50 yo, the most common cause of SVC syndrome is lymphoma.

Which types of NHL are associated with SVC syndrome?

NHL types associated with SVC syndrome:

1.     Diffuse large B-cell lymphoma

2.     Lymphoblastic lymphoma

3.     Primary mediastinal B-cell lymphoma with sclerosis

What is the typical duration of Sx prior to presentation with SVC syndrome?

Pts with SVC syndrome may have Sx over days to wks but usually present within 1 mo of onset.

Do most pts presenting with SVC syndrome have a prior cancer Dx?

No. Most pts presenting with SVC syndrome do not have a prior cancer Dx.

Why is SVC syndrome considered an emergency?

SVC syndrome may cause airway obstruction and cerebral edema; however, severe Sx are uncommon, and life-threatening Sx are rare.

How may pts with SVC syndrome present?

Presenting Sx of SVC syndrome:

1.     Facial fullness

2.     Facial and neck swelling, especially if bending forward

3.     Stridor

4.     Dyspnea

What is the most common Sx of SVC syndrome?

The most common Sx of SVC syndrome is dyspnea.

What physical exam findings are associated with SVC syndrome?

Signs of SVC syndrome: plethora, facial edema, jugular venous distension, and visible collateral venous drainage on the ant chest

image Workup/Staging

Describe the workup of SVC syndrome.

SVC syndrome workup: H&P, assessment of respiratory status, CXR and/or CT chest with contrast (best to visualize the extent of blockage), determination of the best Bx route if Dx is unknown, labs (AFP, LDH, β-HCG), and BM aspirate and Bx

Name 5 ways to obtain tissue Dx for SVC syndrome.

Methods to obtain tissue Dx in SVC syndrome:

1.     Sputum cytology

2.     Bx of palpable LNs

3.     Bronchoscopy

4.     Mediastinoscopy

5.     Video-assisted thorascopic surgery

What is usually seen on CXR in SVC syndrome?

CXR findings in SVC syndrome include a widened mediastinum and the presence of a mass near the SVC.

What CT finding is closely associated with SVC syndrome?

The presence of collateral vessels is a CT finding that closely relates to SVC syndrome.

Why should RT not be given prior to a histologic Dx in SVC syndrome?

RT may obscure the histologic Dx and should be deferred until diagnostic Bx is obtained in SVC syndrome.

image Treatment/Prognosis

What is the 1st step in Tx of SVC syndrome?

The 1st step in treating SVC syndrome is to establish a pathologic Dx, which will determine further interventions.

What Tx may be used for SVC syndrome?

SVC syndrome Tx: RT, chemo, surgery, and stents

What is the role of steroids in SVC syndrome?

Steroids are frequently used in SVC syndrome, but there is limited data to support their use.

In which malignant causes of SVC syndrome is chemo 1st line?

Chemo is the Tx of choice in SVC syndrome caused by lymphoma, germ cell tumors, and SCLC.

Which pts with SVC syndrome may be appropriate for surgery?

Pts with SVC syndrome who do not respond to chemo or RT may be considered for surgical bypass with synthetic grafts or autologous tissue.

What is the most rapid way to manage SVC thrombosis?

The most rapid method to manage SVC thrombosis is by intraluminal stenting.

What Tx should be considered if a pt with SVC syndrome presents with thombosis?

Use anticoagulation therapy for pts with SVC syndrome presenting with thrombosis unless contraindications are present.

Which pts with SVC syndrome require emergent Tx?

SVC syndrome pts with central airway compromise, severe laryngeal edema, or coma secondary to cerebral edema require emergent Tx.

What fractionation is used to emergently treat SVC syndrome?

Fractionation for emergent SVC Tx is 250–400 cGy × 3. There is conflicting retrospective data on the benefit of hypofractionation.

When treating SVC syndrome, what should the RT fields encompass?

RT fields for SVC syndrome include encompassing gross Dz and adjacent nodal tissue while respecting normal tissue toxicity, especially the lungs and heart.

What should guide the total RT dose used for SVC syndrome?

The total RT dose for SVC syndrome depends on the underlying histology (i.e., lung cancers are treated to ≥60 Gy, while lymphomas are treated to 35–45 Gy).

Does SVC syndrome portend a bad prognosis?

No. The prognosis in SVC syndrome depends on the underlying cause rather than the presence of the syndrome itself.

What is the overall symptomatic response to RT in SVC syndrome?

The overall response rate to RT for SVC syndrome is ~60%.

Does RT for SVC syndrome restore normal flow in the SVC?

No. RT for SVC syndrome does not generally restore normal vascular flow despite improving Sx.

What non-Tx event likely contributes to symptomatic improvement in SVC syndrome?

The development of collateral vessels largely contributes to Sx improvement in SVC syndrome.

image Toxicity

What are potential acute toxicities of emergent RT for SVC syndrome?

Potential acute toxicities of emergent RT for SVC −syndrome: fatigue, skin irritation, cough, esophagitis

What are potential subacute and chronic toxicities of RT for SVC syndrome?

Potential subacute and chronic toxicities of RT for SVC syndrome: RT pneumonitis, pericarditis, pulmonary fibrosis, esophageal stenosis