Superior vena cava (SVC) syndrome results from obstruction of blood flow through the SVC, which can be caused by external compression or invasion by adjacent tumors or thrombosis within the SVC. The most common causes are lung cancer, lymphoma, and thrombosis related to intravenous devices. Obstruction of the SVC increases venous blood pressure as collateral veins form, potentially causing symptoms like head and neck swelling, dyspnea, and cough. SVC syndrome is diagnosed based on symptoms and imaging evidence of SVC obstruction.

2.  Superior vena cava (SVC) syndrome results
from any condition that leads to obstruction
of blood flow through the SVC.
 Obstruction can be caused by invasion or
external compression of the superior vena
cava by adjacent pathologic processes
involving the right lung, lymph nodes, and
other mediastinal structures, or by
thrombosis of blood within the SVC.
 In some cases, both external compression
and thrombosis coexist

3.  In the preantibiotic era, syphilitic thoracic
aortic aneurysms, fibrosing mediastinitis, and
other complications of untreated infection
were frequent causes of the SVC syndrome.
 In the postantibiotic era, malignancy became
the most common cause.
 More recently, the incidence of SVC
syndrome due to thrombosis has risen,
largely because of increased use of
intravascular devices such as catheters and
pacemaker wires.

4. PATHOPHYSIOLOGY —
 Obstruction of the SVC can be caused by
invasion or external compression by adjacent
pathologic processes involving the right lung,
lymph nodes, or other mediastinal
structures, or by thrombosis of blood within
the SVC.
 As the flow of blood within the SVC becomes
obstructed, venous collaterals form,
establishing alternative pathways for the
return of venous blood to the right atrium.

5.  Collateral veins may arise from the azygos,
internal mammary, lateral thoracic,
paraspinous, and esophageal venous systems.
 The venous collaterals dilate over several
weeks.
 As a result, upper body venous pressure is
markedly elevated initially but decreases
over time.
 However, even when well-developed
collateral drainage patterns are present,
central venous pressures remain elevated,
producing the characteristic signs and
symptoms of SVC syndrome.

6.  The rapidity of onset of symptoms and signs
from SVC obstruction depends upon the rate
at which complete obstruction of the SVC
occurs in relation to the recruitment of
venous collaterals.
 Patients with malignant disease may develop
symptoms of SVC syndrome within weeks to
months because rapid tumor growth does not
allow adequate time to develop collateral
flow.

7.  The interstitial edema of the head and neck
is visually striking but generally of little
clinical consequence.
 However, edema may narrow the lumen of
the nasal passages and larynx, potentially
compromising the function of the larynx or
pharynx and causing dyspnea, stridor, cough,
hoarseness, and dysphagia.
 In addition, cerebral edema can also occur
and lead to cerebral ischemia, herniation,
and possibly death.
 Cardiac output may be diminished transiently
by acute SVC obstruction, but within a few
hours, blood return is reestablished by
increased venous pressure and collaterals.

8.  Hemodynamic compromise, if present, more
often results from mass effect on the heart
than from SVC compression

9.  Etiology :
 Malignancy —
 An intrathoracic malignancy is responsible
for 60 to 85 percent of cases of SVC
syndrome.
 Non-small cell lung cancer (NSCLC) is the
most common malignant cause of SVC
syndrome, accounting for 50 percent of all
cases , followed by small cell lung cancer
(SCLC, 25 percent of all cases) and non-
Hodgkin lymphoma (NHL, 10 percent of
cases).
 Together, lung cancer and NHL are
responsible for approximately 95 percent of
cases of SVC syndrome that are caused by
malignancy .

10.  Lung cancer —
 Approximately 2 to 4 percent of patients with lung
cancer develop SVC syndrome at some point during
their disease course .
 SVC syndrome is more common with SCLC, occurring
in approximately 10 percent of cases at presentation.
 This is presumably because SCLC develops and grows
rapidly in central rather than peripheral airways.
 Fewer than 2 percent of patients presenting with
NSCLC have SVC syndrome as a complication, but
because of the higher incidence, NSCLC is a more
frequent cause of SVC syndrome than is SCLC .
 Venous obstruction in these cases results from
extrinsic compression of the SVC by either the
primary tumor or enlarged mediastinal lymph nodes,
or as a result of direct tumor invasion of the SVC .

11.  Lymphoma —
 SVC syndrome develops in 2 to 4 percent of
cases of NHL.
 Diffuse large cell and lymphoblastic
lymphomas are the most common subtypes
that are associated with SVC syndrome.
 SVC syndrome is even more common in
patients with primary mediastinal large B-
cell lymphoma with sclerosis, an unusual and
aggressive NHL subtype that represents 3 to 7
percent of all diffuse large-cell lymphomas.
 Patients typically present with a rapidly
enlarging anterior mediastinal mass,
frequently with associated SVC syndrome.

12.  Although most NHLs cause SVC syndrome by
extrinsic compression due to enlarged lymph
nodes , patients with intravascular
(angiotropic) lymphoma have intravascular
occlusion as the primary pathogenic
mechanism .
 Other — Other malignant tumors that are
less commonly associated with the SVC
syndrome include : thymoma, primary
mediastinal germ cell neoplasms,
mesothelioma, and solid tumors with
mediastinal lymph node metastases (eg,
breast cancer)

13.  Nonmalignant disorders —
 Nonmalignant conditions account for 15 to
40 percent of SVC obstructions.
 Although the incidence of SVC syndrome due
to infections such as tuberculosis and syphilis
has decreased, there has been an increase in
SVC thrombosis associated with the presence
of intravascular devices such as central
venous catheters and cardiac pacemaker
leads

14.  Clinical maniestations:
 Regardless of etiology, dyspnea is the
most common symptom .
 In addition, patients frequently complain
of facial swelling or head fullness, which
may be exacerbated by bending forward
or lying down.
 Other symptoms include arm swelling,
cough, chest pain, or dysphagia.
 Patients with cerebral edema may have
headaches, confusion, or possibly coma.

15.  On physical examination, the most common
findings are facial edema and venous distension
in the neck and on the chest wall .
 Arm edema, cyanosis, and facial plethora can be
seen.
 In most cases, symptoms are gradually
progressive over several weeks and then get
better over time, due to the development of
venous collaterals.