Francesco Puma and Jacopo Vannucci
The superior vena cava (SVC) originates in the chest, behind the first right sternocostal
articulation, from the confluence of two main collector vessels: the right and left
brachiocephalic veins which receive the ipsilateral internal jugular and subclavian veins. It
is located in the anterior mediastinum, on the right side.
The internal jugular vein collects the blood from head and deep sections of the neck while
the subclavian vein, from the superior limbs, superior chest and superficial head and
received by the brachiocephalic veins.
After the brachiocephalic convergence, the SVC follows the right lateral margin of the
sternum in an inferoposterior direction. It displays a mild internal concavity due to the
adjacent ascending aorta. Finally, it enters the pericardium superiorly and flows into the
right atrium; no valve divides the SVC from right atrium.
The SVC’s length ranges from 6 to 8 cm. Its diameter is usually 20-22 mm. The total
diameters of both brachiocephalic veins are wider than the SVC’s caliber. The blood
pressure ranges from -5 to 5 mmHg and the flow is discontinuous depending on the heart
The SVC can be classified anatomically in two sections: extrapericardial and intrapericardial.
The extrapericardial segment is contiguous to the sternum, ribs, right lobe of the thymus,
connective tissue, right mediastinal pleura, trachea, right bronchus, lymphnodes and
ascending aorta. In the intrapericardial segment, the SVC enters the right atrium on the
upper right face of the heart; in front it is close to the right main pulmonary artery. On the
right side, the lung is in its proximity, separated only by mediastinal pleura. The right
phrenic nerve runs next to the SVC for its entire course  (Figure 1).
The SVC receives a single affluent vein: the azygos vein. The azygos vein joins the SVC from
the right side, at its mid length, above the right bronchus. The Azygos vein constantly
receives the superior intercostal vein, a large vessel which drains blood from the upper two
or three right intercostal spaces. In the case of SVC obstruction, the azygos vein is
responsible for the most important collateral circulation. According to the expected
collateral pathways, the SVC can be divided into two segments: the supra-azygos or
Topics in Thoracic Surgery
systems which were first described in 1949 by McIntire and Sykes. They are represented by
the azygos venous system, the internal thoracic venous system, the vertebral venous system
and the external thoracic venous system . The azygos venous system is the only direct
path into the SVC. The internal thoracic vein is the collector between SVC and inferior vena
cava (IVC) via epigastric and iliac veins. The vertebral veins with intercostals, lumbar and
sacral veins, represent the posterior network between SVC and IVC. The external thoracic
vein system is the most superficial and it is represented by axillary, lateral thoracic and
superficial epigastric veins.
The SVC is a constituent part of the right paratracheal space (also called “Barety's space”),
containing the main lymphatic route of the mediastinum, i.e. the right lateral tracheal
chain. Barety's space is bounded laterally by the SVC, posteriorly by the tracheal wall,
and medially by the ascending aorta. The nodes of the right paratracheal space are
frequently involved in malignant growths: the SVC is undoubtedly the anatomical
structure of this space which offers less resistance to compression, due to its thin wall and
low internal pressure.
Anatomical anomalies are rare. The most frequent is the double SVC which has an
embryologic etiology .
Superior Vena Cava Syndrome
SVC syndrome (SVCS) may be related to various etiological factors. Malignancies are
predominant (95%) while, in the past, infectious diseases used to be common. During the
last century, progression in anti-bacterial therapies and improvement in social conditions
have led to a consistent decrease in the benign origin of this condition. The incidence of
iatrogenic SVCS is currently increasing [3,4].
SVCS etiology is summarized as follows:
Mediastinal germ cell tumors
Leiomyosarcoma and angiosarcoma
Anaplastic thyroid cancer
Fibrosing mediastinitis (idiopathic or radiation-induced)
Infectious diseases (tubercolosis, histoplasmosis, echinococcosis, syphilis,
aspergillosis, blastomycosis, filariasis, nocardiosis…)
Lymphadenopaties (sarcoidosis, Behçet’s syndrome, Castelman’s disease…)
Pericardial, thymic, bronchogenic cysts
Pacemaker and defibrillator placement
Central venous catheters
The pathogenetic basis of SVCS is obstruction to the blood flow. It can result from
intrinsic or extrinsic obstacles. The former are uncommon and are represented by
thrombosis or invading tissue. Extrinsic factors develop from compression or stricture of
In physiologic conditions, blood return to the right atrium is facilitated by the pressure
gradient between the right atrium and venae cavae. When obstruction of the SVC occurs, the
vascular resistances rise and the venous return decreases. SVC pressure may increase
When SVC shows a significant stenosis (3/5 of the lumen or more), blood flow is redirected
through the collateral circulation in order to bypass the obstruction and restore the venous
implications. In acute impairments, the blood flow is not rapidly distributed through the
collateral network so symptoms arise markedly. In the case of slow-growing diseases, the
collateral venous network has enough time to expand in order to receive the circulating
volume. For this reason, long-lasting, severe SVC obstruction can sometimes be found
without significant related signs and symptoms [3,6].
The SVC wall does not offer resistance to compression. When SVC lumen reduction is
greater than 60%, hemodynamic changes occur: proximal dilatation, congestion and flow
slowdown. The clinical signs of this condition are mainly represented by cyanosis (due to
venous stasis with normal arterial oxygenation) and edema of the upper chest, arms, neck
and face (periorbital initially). Swelling is usually more important on the right side, because
of the better possibility of collateral circulation in the left brachiocephalic vein compared to
the contralateral (Figure 2). Vein varicosities of the proximal tongue and dark purple ears
are also typical. Other signs or symptoms are: coughing, epistaxis, hemoptysis, dysphagia,
dysphonia and hoarseness (caused by vocal cord congestion), esophageal, retinal and
conjuntival bleeding. In the case of significant cephalic venous stasis, headache, dizziness,
buzzing, drowsiness, stupor, lethargy and even coma may be encountered. Headache is a
common symptom and it is usually continuous and pressing, exacerbated by coughing.
Epilepsy has been occasionally reported as well as psychosis, probably due to carbon
dioxide accumulation [3,4,7-14]. Dyspnea can be directly related to the mediastinal mass or
be caused by pleural effusion or cardiocirculatory impairment. Supine position may worsen
the clinical scenarios.
return is distributed through a collateral circulation, mainly sustained by branches of
the left brachiocephalic vein. Edema in this patient was more severe in the right arm than
Level of obstruction and rapidity of development, determining the effectiveness of
Impairment of lymphatic drainage (pulmonary interstitial edema or pleural effusion)
Involvement of other mediastinal structures (compression or invasion of heart,
pulmonary artery and central airways, phrenic nerve paralysis…)
Intolerance of the supine position is always linked to a severe prognostic significance for
patients with mediastinal syndromes . The variation in decubitus may worsen the
already existing signs and symptoms: in the supine position, an anterior mediastinal mass
may compress the trachea or the heart by means of gravity, with possible cardiorespiratory
problems. Direct compression of the common trunk of the pulmonary artery is also possible,
although this is not as likely to happen, given that such structure is cranially protected by
the aortic arch .
The presence of dyspnea at rest, especially in the sitting position, carries a severe prognostic
significance in patients with mediastinal syndromes. Dyspnea at rest can be caused by either
cardiovascular or respiratory problems:
pulmonary congestion caused by lymphatic stasis
combination with pulmonary atelectasis
direct compression of the mass on the airways, on the heart, or on the pulmonary
considered as a high risk factor for invasive procedures under general anesthesia. If the
shortness of breath is related to laryngeal edema, the patient should not be presented for
general anesthesia and surgery.
Superficial dilated vascular routes are the main sign of collateral circulation and appear
swollen and non-pulsating. In the case of marked obesity, superficial veins can be missing at
inspection. The variety of collateral circulation and the differences in the venous re-
arrangement are expression of the SVC obstruction site (Figure 3,4,5).
The anatomic classification includes three levels of obstruction:
1. Obstruction of the upper SVC, proximal to the azygos entry point.
2. Obstruction with azygos involvement.
3. Obstruction of the lower SVC, distal to the azygos entry point.
1. In this situation, there is no impediment to normal blood flow through the azygos vein
which opens into the patent tract of the SVC. Venous drainage coming from the head
neck, shoulders and arms cannot directly reach the right atrium. A longer but effective
way is provided by several veins, the most important being the right superior
intercostal vein. From the superior tract of the SVC, blood flow is reversed and directed
to the azygos, mainly through the right superior intercostal vein. The azygos collateral
system is eminently deep; therefore the presence of superficial vessels is usually
lacking, even if possible in the area of the internal thoracic vein’s superficial tributaries.
The volumetric increase of the vessels can be consistent and capacity may increase up to
eight times. The efficiency of this collateral route is reliable, thus the clinical
compensation is unbalanced only in the case of a rapid development of the obstruction
or if the stenosis is more than 90% (Figure 3).
2. In this case, the azygos vein cannot be available as collateral pathway and the only
viable blood return is carried by minor vessels to IVC (cava-cava or anazygotic
circulation). From the internal thoracic veins, blood is forced to the intercostal veins,
then to azygos and emiazygos veins. The flow is thus reversed into the ascending
lumbar veins to the iliac veins. Direct anastomosis between the azygos’ origin and the
IVC and between emiazygos and left renal vein are also active. In addition, the
internal thoracic veins can flow into the superior epigastric veins. From the superior
epigastric veins, blood is carried to the inferior epigastric veins across the superficial
system of the cutaneous abdominal veins and finally to the iliac veins. Another course
is between the thoraco-epigastric vein (collateral of the axillary vein) and the external
In these conditions, the collateral circulation is partly deep and partly superficial. The
physical examination often reveals SVC obstruction. The reversed circulation through
the described pathways, remains less efficient than the azygos system and venous
hypertension is usually more severe. For this reason, this kind of SVC obstruction is
often related to important symptoms, dyspnea and pleural effusion. The ensuing slow
blood flow may be responsible for superimposed thrombosis. In the disease
progression, renal impairment can evolve as the SVC obstruction affects the lumbar
plexus (mostly the ascending lumbar veins, left side) which congests the renal vein
Fig. 4. Obstruction with azygos involvement. Collateral pathways.
3. In this condition, the obstruction is just below the azygos arch. The blood flow is
distributed from the superior body into the azygos and emiazygos veins, in which the
flow is inverted, to the IVC tributaries. In this type of case, the superficial collateral
system is not always evident but the azygos and emiazygos congestion and dilatation
are usually important. The hemodynamic changes lead to edema and cyanosis of the
upper chest and pleural effusion. Pleural effusion is often slowly-growing and right-
sided, probably due to anatomical reasons: there is a wider anastomosis between
emiazygos and IVC than between azygos and IVC  (Figure 5).
Fig. 5. Obstruction of the lower SVC, distal to the azygos entry point. Collateral pathways.
Several classifications of SVCS have been proposed even though further investigations are
required to achieve a definitive staging system. There are three main classification proposals
which follow different methods of categorization [18-20].
1. Doty and Standford’s classification (anatomical)
Type I: stenosis of up to 90% of the supra-azygos SVC
Type II: stenosis of more than 90% of the supra-azygos SVC
Type III: complete occlusion of SVC with azygos reverse blood flow
Type IV: complete occlusion of SVC with the involvement of the major tributaries
and azygos vein
2. Yu’s classification (clinical)
Grade 0: asymptomatic (imaging evidence of SVC obstruction)
Grade 1: mild (plethora, cyanosis, head and neck edema)
Grade 2: moderate (grade 1 evidence + functional impairment)
Grade 3: severe (mild/moderate cerebral or laryngeal edema, limited cardiac
Grade 4: life-threatening (significant cerebral or laryngeal edema, cardiac failure)
Grade 5: fatal
3. Bigsby’s classification (operative risk)
The authors proposed an algorithm for SVCS to assess the operative risk in order to submit
the patient to invasive diagnostic procedures. The low risk patients present: no dyspnea at
rest, no facial cyanosis in the upright position, no change of dyspnea and no worsening of
facial edema and cyanosis, during the supine position. The high risk patients present facial
cyanosis or dyspnea at rest in the sitting position.
Physical examination is often crucial: the presence of edema and superficial venous
network of the upper chest may support the clinical diagnosis. Imaging studies are
however required. Most cases are suspected at the standard chest X-ray and the
most common radiological findings are right mediastinal widening and pleural effusion
evaluation of the mediastinal syndromes. CT imaging is widely employed in SVCS
assessment because of its large availability and short acquisition time. Intravenous contrast
should be administered, in order to provide high-quality vascular imaging. Contrast
enhanced multidetector CT may show the site of the obstruction, some aspects of the
primary disease and eventual intraluminal thrombi. Multiplanar and 3D reconstructions
may provide better image detection and definition. The contrast flow can also help to
distinguish the extent of the collateral network (Figure 6) .
Fig. 6. Angio-CT scan: Obstruction of the lower SVC, distal to the azygos entry point.
occurs by means of IVC.
Magnetic resonance imaging (MRI) plays a side role; it is indicated when CT cannot be
performed (e.g. pregnancy, endovenous contrast intollerance). The long acquisition times of
MRI limit its use in critically ill patients.
Invasive venography is now rarely used due to the huge improvement in vascular CT
imaging. It is currently performed only as a preliminary to operative procedures such as
Once the thoracic imaging is obtained, the work-up should include brain, abdominal and
bone studies in view of the probable malignant nature of the primary lesion. Recently
Fluorodeoxyglucose-Positron Emission Tomography has gained an important role in
The histological definition remains the key factor for the causative treatment, in the case of
neoplastic etiology. Superficial adenopathies have to be carefully investigated in order to
find a possible source of tissue and the easiest target for biopsy. The invasive diagnostic
procedure varies largely depending on the suspected malignancy and its site. The biopsy
can be obtained through traditional bronchoscopy or echo-guided endoscopy, superficial
node biopsy, mediastinoscopy, mediastinotomy, transthoracic needle biopsy, thoracoscopy,
cervical or supraclavicular biopsies; thoracotomy and sternotomy are rarely indicated.
Operative endoscopy has gained a new significance in the evaluation of SVCS since
echography has been introduced but the best diagnostic result is still obtained by the
mediastinoscopy. Venous hypertension may increase the procedure-related risk [23-27].
Therapy should be causative. Syndrome management recognizes different levels of priority
depending on the severity of symptoms, etiology and prognosis. SVCS needs a
multidisciplinary approach and symptoms relief is often the first objective of complex care.
diagnosed as advanced-stage malignancies.
The patient must immediately assume an orthostatic position. Other supportive treatments
are usually promptly established; oxygen, diuretics, and steroids are also suggested. The
risk of an overlying thrombosis is particularly high and anticoagulant therapy should be
In case of malignancy, the treatment can have palliative or, rarely, curative intent.
Chemotherapy is usually employed in lymphomas, small-cell lung cancer and germ cell
tumors. Besides chemotherapy, radiotherapy is widely used in the treatment of non-small cell
lung cancer. Radiation therapy can obtain good results but can also produce an initial
inflammatory response with a possible temporary worsening [28,29]. Some cases must be
approached as an emergency. In this type of situation, the treatment of choice is usually
endovascular with the aim of restoring blood flow as soon as possible. The acute life-
threatening presentation is the only situation in which radiotherapy before histological
diagnosis can be considered. However, this approach should be avoided, whenever possible.
Endovascular stenting provides fast functional relief. It is the best option in an emergency
and sometimes the clinical benefit is immediate. It is also advocated in the case of chemo-
radiotherapy non-responders .
Surgery has a central role in the diagnosis but rarely in the therapy. A SVC resection and
reconstruction is not often recommended and is a demanding procedure. The main proposal
for SVC resection is direct infiltration in thymomas or in N0-N1 non-small cell lung cancer.
In the case of infiltration of less than 30% of the SVC circumference, direct suture is favored
(Figure 7). Larger involvements require a prosthetic repair. Different methods of SVC repair
have been investigated using different materials (Figures 8, 9, 10a-b). Armoured PTFE grafts
and biologic material are the preferred choices. Morbidity after SVC surgical procedures is
high and the post-operative care must be intensive . Long-term patency of a SVC by-pass
graft is uncertain but, usually, the slow onset of the graft thrombosis favors the
development of effective collateral circulation.
Fig. 7. SVC resection for limited infiltration by a right upper lobe NSCLC. The moderate
Fig. 8. Graft reconstruction by end-to-end anastomosis between proximal and distal SVC.
Fig. 9. Graft reconstruction of SVC by end-to-end anastomosis between the right
Fig. 10a. Graft reconstruction of SVC by end-to-end anastomosis between the left
brachiocephalic vein and the SVC.
Fig. 10b. Armoured PTFE reconstruction of SVC by end-to-end anastomosis between the left
Artworks by Walter Santilli R.N. and Elisa Scarnecchia M.D.
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