AJR 2001; 176:211-213
© American Roentgen Ray Society
Systemic-to-Pulmonary Venous Shunt in Superior Vena Cava Obstruction Revealed on Dynamic Helical CT
David Grayet1,
Benoit Ghaye,
David Szapiro and
Robert F. Dondelinger
1
All authors: Department of Medical Imaging, University Hospital Sart Tilman
B35, B-4000 Liege 1, Belgium.
Received January 27, 2000;
accepted after revision June 2, 2000.
Address correspondence to R. F. Dondelinger.
Introduction
Obstruction of the superior vena cava is frequently associated with the
formation of collateral veins involving mainly the azygos-hemiazygos system,
the paravertebral venous network, and the internal and lateral thoracic veins.
Systemic-to-pulmonary venous shunts may also occur in rare cases
[1]. These shunts consist of
mediastinal connections between the innominate veins and the superior
pulmonary veins, through bronchial venous plexuses developed around the
airways, hilar vessels, and pleura. We report two patients in whom these
shunts were shown on angiodynamic helical CT and three-dimensional
reformatting.
Case Report
A 58-year-old man was admitted to the hospital for progressive hoarseness,
dysphonia, and cough. The patient also complained of headache and dizziness.
His medical history included myocardial infarction treated by aortocoronary
bypass. Physical examination showed right lateral swelling of the neck and
right vocal cord palsy. Chest radiographic findings revealed a right-sided
hilar mass, widening of the right tracheal stripe, and tracheal displacement.
The carcinoembryonic antigen level was 14.7 ng/mL (normal level, <5 ng/mL),
and the neuron-specific enolase level was 15.8 ng/mL (normal level, <12.5
ng/mL). Bronchoscopy showed moderate extrinsic compression of the tracheal
lumen and infiltration of the distal trachea and right mainstem bronchial
wall. Transbronchial biopsy confirmed small cell lung cancer.
Thoracic staging was performed using helical CT (PQ 5000; Picker
International, Cleveland, OH). Two consecutive acquisitions were obtained
after the IV injection of 120 mL of ioversol ([300 mg I/mL] Optiray; Guerbet,
Aulnay-sous-Bois, France) through a right upper arm vein with a power injector
at a rate of 2 mL/sec. The patient was placed supine with the arms elevated to
minimize artifacts. The first helical scan, obtained 20 sec after the start of
injection, included the area from the right inferior pulmonary vein to the
cervicothoracic junction. The scanning protocol was as follows: 5-mm slice
thickness, 3-mm increment, and a pitch of 1.5. The next helical scan covered
the lung bases using a slice thickness of 10 mm, an increment of 8 mm, and a
pitch of 1.5. Sequential high-resolution CT was performed, covering the entire
lung at 10-mm intervals. Helical CT data were transferred to a work-station
(Voxel Q; Picker International). Maximum-intensity-projection and
volume-rendering reconstructions were obtained in various projections.
CT showed a tight stenosis of the superior vena cava and an occlusion of
both innominate veins at the confluence caused by a bulky 6.5 x 4
x 9.5 cm mass extending from the right pulmonary hilum to the right
lateral aspect of the trachea. The left superior pulmonary vein and the left
heart were intensely opacified before opacification of the right heart and the
pulmonary artery (Fig.
1A,1B,1C).
This right-to-left shunt was related to early filling of mediastinal venous
collaterals connecting the left innominate vein and the left superior
pulmonary vein. Other collateral venous pathways, such as the azygos and
hemiazygos veins, the right internal thoracic vein, and the vertebral venous
plexus, were also seen. Despite systemic chemotherapy with cisplatin
(Platinol; Bristol-Myers Squibb, Brussels, Belgium) and etoposide (Vepesid;
Bristol-Myers Squibb), the superior vena cava syndrome worsened, and the
patient was treated with corticosteroids and adjuvant radiotherapy.
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Fig. 1A. —58-year-old man with systemic-to-pulmonary venous shunt.
Helical CT scan shows tight stenosis of superior vena cava (curved
arrow) and obstruction of distal part of left innominate vein (open
arrow) caused by tumor encasement (T). Mediastinal venous network is
densely opacified (small white arrows). Note opacification of azygos
vein (thick white arrow), accessory hemiazygos vein
(arrowhead), and perivertebral plexus.
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Fig. 1B. —58-year-old man with systemic-to-pulmonary venous shunt.
Helical CT scan 3 cm caudal to A shows early enhancement of aorta (236
H) after IV contrast injection (pulmonary artery, 180 H). Note opacification
of right internal thoracic vein (thick arrow), opacified dilated
bronchial veins (arrowheads), and mediastinal venous network
(small arrows).
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Fig. 1C. —58-year-old man with systemic-to-pulmonary venous shunt.
Helical CT scan 2 cm caudal to B shows left superior pulmonary vein
(asterisk), dilated bronchial veins (arrowheads) and
mediastinal venous network (small arrows) with higher attenuation
(500 and 1250 H, respectively) than superior vena cava, pulmonary artery, and
right superior pulmonary vein (180 H) (thick arrow).
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CT performed after treatment showed reduction in the size of the mass to a
diameter of 1 cm. Right and left innominate veins were patent. Venous
collaterals were no longer observed, and sequential opacification of cardiac
chambers was unremarkable.
Discussion
Systemic-to-pulmonary venous shunt is a condition that is reported in the
literature only in isolated case reports
[1]. These right-to-left shunts
are typically associated with superior vena cava obstruction, usually caused
by malignant tumor and rarely caused by benign conditions. Classically, in
cases of superior vena cava obstruction, blood drains into the
azygos-hemiazygos system, the lateral and internal thoracic veins, and the
paravertebral network [2].
Unusual connections may be established between a systemic vein and a pulmonary
vein that result in a right-to-left shunt. These shunts can be formed by
different mechanisms: anatomic, congenital, or acquired.
In the anatomic type, bronchial veins and pulmonary veins are
interconnected through already existing bronchial venous plexuses. These
plexuses are located in the bronchial wall and the peribronchovascular
connective tissue, acting as vasa vasorum. As a result, bronchial veins
predominantly drain into the right atrium through the pleurohilar bronchial
veins, and approximately one third of their flow is into the left atrium
through the pulmonary veins
[3,4,5].
In normal conditions, the pleurohilar bronchial veins communicate with the
azygos and hemiazygos veins. Valves are usually located at the junction of
pleurohilar bronchial veins with azygos and hemiazygos veins, preventing
backflow into the pleurohilar bronchial veins. If pressure rises (as occurs in
cases of superior vena cava obstruction), the valves may become incompetent,
resulting in a right-to-left shunt by reversed flow. The right-to-left shunt
is most likely of the anatomic type.
In the congenital type of shunt, three shunting pathways are distinguished:
an aberrant pulmonary venous return with reversed flow, a levoatriocardinal
embryologic remnant (connecting the posterior cardinal system with pulmonary
veins) [6,
7], and a persistent left
superior vena cava (occasionally seen as a thin channel draining into the
right atrium or, rarely, into the left superior pulmonary vein or left
atrium). The acquired shunt is basically of inflammatory origin and results in
newly formed vessels bridging the subpleural pulmonary veins and the
intercostal veins through pleural adhesions
[1].
In our first patient, imaging revealed the shunt's location in a normal
pleuropulmonary area, thus excluding the possibility of an acquired shunt.
Furthermore, no unique shunting vein was shown on CT, but rather several
dilated pleurohilar bronchial veins draining into the left pulmonary vein,
thus excluding a congenital shunt.
The second patient was a 70-year-old woman who was admitted for cervical
and periscapular edema extending to both arms. Her medical history included a
right-sided mastectomy and axillary lymphadenectomy for infiltrative ductal
epidermoid carcinoma, followed by radiotherapy and chemotherapy. Angiodynamic
helical CT showed stenosis of the superior vena cava and occlusion of the
azygos vein caused by mediastinal adenopathy. The lateral and internal
thoracic, azygos, and perivertebral veins were visualized, as was early
opacification of the right superior pulmonary vein preceding opacification of
the pulmonary arteries (Fig.
2). The shunt was located in the right upper lobe and no unique
shunting vein was seen, thereby excluding a congenital shunt. The pleurohilar
bronchial veins drained into the right superior pulmonary vein.
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Fig. 2. —70-year-old woman with systemic-to-pulmonary venous shunt.
Helical CT scan shows earlier enhancement of right branches of superior
pulmonary vein (thick arrows), dilated bronchial veins
(arrowheads), and mediastinal venous network (small arrow)
than of aorta, left pulmonary vein (asterisk), and pulmonary artery.
Aorta (192 H) shows higher attenuation than pulmonary artery (148 H),
indicating presence of right-to-left shunt.
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Reported methods for depicting a right-to-left shunt include radionuclide
studies using 99mTc-aggregated albumin
[8] and phlebography
[9]. Conventional
[1] and helical
[10] CT are also reported to
be occasionally diagnostic.
In our patients, angiodynamic helical CT showed the right-to-left shunts
and their locations, giving information superior to that of other imaging
techniques. Angiodynamic helical CT revealed early contrast enhancement of the
left heart or pulmonary veins before pulmonary arteries and showed the filling
of pleurohilar bronchial veins.
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