Imaging of SVC using different modalities and understanding the embryology of SVC and its pathologies.

1. ANATOMY, EMBRYOLOGY AND
IMAGING OF SUPERIOR VENA
CAVA.
DR. GAJANAN WATTAMWAR
JR1 RADIODIAGNOSIS.
16.09.2022

2. INTRODUCTION
• The superior vena cava (SVC) is the largest central systemic vein in the
mediastinum.
• Imaging (ie, radiography, computed tomography [CT], magnetic resonance [MR]
venography, and conventional venography) plays an important role in identifying
congenital variants and pathologic conditions that affect the SVC.
• Knowledge of the basic embryology and anatomy of the SVC and techniques for
CT, MR imaging, and conventional venography are IMPORTANT to accurately
diagnosis and clinical decision making.

3. • Congenital anomalies such as Persistent left SVC, Partial anomalous
pulmonary venous return, and Aneurysm are asymptomatic and may be
discovered incidentally in patients undergoing imaging evaluation for
associated cardiac abnormalities or other indication.
• Familiarity with congenital abnormalities is important to avoid image
misinterpretation.

4. ANATOMY OF SUPERIOR VENA CAVA

5. COURSE AND DIAMETER
• The SVC is formed by the confluence of the right and left brachiocephalic
veins. It courses along the right middle mediastinum, with the trachea and
ascending aorta on its left, and drains into the right atrium.
• Extent - From First intercostal space to Right 2nd intercostal space
• The mean length of the SVC is 7.1 cm ± 1.4, and its maximum diameter in
adults is 2.1 cm ± 0.7.
• An SVC area of less than 1.07 cm2 is an accurate threshold for SVC
obstruction or compression.

6. • The azygos vein is a major tributary that travels along the right anterior
borders of the thoracic vertebrae up to the level of the carina and then
traverses the middle mediastinum, arching over the right
tracheobronchial angle to drain posteriorly into the distal SVC.
• In case of SVC obstruction the veins getting prominent are :
Azygos–hemiazygos–accessory hemiazygos system,
Mediastinal venous plexus,
Diaphragmatic venous plexus
Lateral thoracic and superficial thoracoabdominal venous plexus,
 Abdominal venous collaterals

7. Branches and Tributaries of the Superior Vena Cava
□ Left brachiocephalic (innominate) vein
• Left subclavian vein
• Left internal jugular vein
• Left superior intercostal vein
□ Right brachiocephalic (innominate) vein
• Right subclavian vein
• Right internal jugular vein
□ Azygos vein
• Hemiazygos vein
• Accessory hemiazygos vein

9. EMBRYOLOGY
• THREE basic venous system
of human foetal circulation
1.Vitelline veins
2.Umbilical veins
3.Somatic (Cardinal veins)

12. • Anomalies of persistent left superior vena cava.

13. IMAGING
• Imaging plays an important role in diagnosis and management of
various conditions that affect the SVC.
• Doppler ultrasonographic (US) evaluation of the SVC is limited
because of the poor acoustic window.
• Direct visualization of the SVC is better obtained at computed
tomography (CT) or magnetic resonance (MR) imaging.
• Contrast agent–enhanced venography with use of digital subtraction
is reserved for interventional procedures and when CT and MR
imaging findings are nondiagnostic

14. On Chest Radiography
• SVC forms an interface along the upper
right mediastinal border that fades above
the medial end of the clavicle
• Frontal and, when obtained, lateral
radiographs are the primary imaging tools
used to evaluate normal positioning of
central venous catheters (CVCs) and
peripherally inserted central catheters
(PICCs).

15. On Computed Tomography
Nonenhanced CT—
• Nonenhanced CT images can demonstrate SVC duplication, narrowing,
and enlargement.
• It can also show CVC (Central venous catheter) position.
• It can be used to visualize calcifications along the SVC that could be
caused by calcified thrombi, fibrin sheaths, or retained catheter or
implantable cardioverter-defibrillator lead fragments.

16. Contrast-enhanced CT.—
• The SVC can be studied during routine contrast-enhanced chest CT.
• Routine contrast-enhanced CT of the chest, performed 60–75 seconds after
injecting contrast agent into a peripheral vein, achieves excellent uniform
enhancement of the SVC.
• Difficulties in CT imaging might be faced due to
• 1. Streak artifacts due to dense contrast media, which can be minimized by
diluted contrast and adjusting the settings according to the viewer.
• 2. Mixing artifacts due to nonenhanced blood from contralateral veins and the
azygos vein, which can mimic a thrombus.

17. STREAK ARTIFACT MIXING ARTIFACT

18. • Routine Protocol:
• Contrast volume and concentration :
Weight based (1 mL/kg; iodine concentration, 350 mg/mL)
• Flow rate: 2.5- 3 mL/sec
• Acquisition delay :40–60 sec
• Contrast agent volume overestimation in obese patients; volume
adjusted to body surface area is more appropriate

19. Magnetic Resonance Venography
Conventional non contrast MR imaging is done
usually to:
 Locate the location and extent of strictures
 Collateral pathways
 Endoluminal thrombus,
 Tumor proliferation

20. • Contrast-enhanced MR venography is a particularly well suited technique
for this anatomic region and can be especially advantageous in patients
with impaired renal function, who have a dialysis shunt, fistula or long time
central catheter placement.
• The SVC can also be evaluated by using a blood pool–specific contrast agent
(Gadopentetate Dimeglumine 469mg/ml )
• In our institute we follow the protocol including the TRICKS sequence
• TRICKS sequence ( Time Resolved Imaging of Contrast KineticS) which
obtains series of images displaying passage of contrast bolus.

21. • We use the antecubital vein and pass 15
ml of contrast followed by 15 ml of Saline
• The acquisition is done at around 40 sec
for the venography.
• MR venography has been shown to be
equally sensitive and specific compared
with conventional venography to evaluate
central venous obstruction

22. Doppler Ultrasound and
Echocardiography
 Direct visualization of the SVC at
Doppler US is challenging.
 A limited role for Doppler US in
evaluation of the proximal SVC with
use of suprasternal and right
supraclavicular window settings

23. Digital Subtraction Imaging Of SVC
• Superior venacavography is performed with simultaneous bilateral injection
of 25 mL of a nonionic contrast medium into the basilic, cephalic, or
antecubital vein through an 18- to 20-gauge peripherally inserted
intravenous catheter.
• Digital subtraction is usually required to adequately visualize the SVC.
Nonenhanced inflow from other central veins should not be mistaken for
thrombus or other filling defects.
• One of the major advantages of conventional arm venography is an ability
to proceed directly to an intervention if an abnormality amenable to
treatment is found

25. Congenital Variants
• Persistent Left SVC
• Right upper lobe partial anomalous pulmonary venous
return
• SVC Aneurysm (Following congenital wall weakness)

26. Persistent Left SVC
• Persistent left SVC is the most common
congenital thoracic venous anomaly.
• In the midportion, the vessel lies anterior
to the left hilum and then traverses along
the ligament of Marshall to drain into the
right atrium via a dilated coronary sinus .
• Persistent left SVC should be suspected
when a dilated coronary sinus is seen at
cross-sectional imaging

27. PAPVR(Partial anomalous pulmonary venous return
• One or more pulmonary veins drain into the systemic venous system or
right atrium rather than the left atrium.
• Right upper lobe PAPVR is a subset of this condition in which the right
upper lobe pulmonary vein drains directly into the SVC.
• Pediatric studies suggest a high association of right upper lobe PAPVR
with sinus venosus atrial septal defect in 80%–90% of patients whereas a
recent study in adults showed a moderate association of 47%

29. SVC ANEURYSM
• SVC aneurysm is extremely rare and is
asymptomatic that may be found
incidentally at imaging performed for
other indications.
• Causes include congenital weakness in
the SVC wall or absence of the
longitudinal muscle layer in the tunica
adventitia .
• There are no strict size criteria for
diagnosis, and saccular and fusiform
types have been described.

30. Acquired Abnormalities
• Stricture
• Fibrin sheath
• Thrombus
• Trauma
• Primary neoplasms
1. SVC Lipoma or Extension of Lipomatous Hypertrophy of the Interatrial
Septum
2. Primary SVC Sarcoma or Leiomyosarcoma

31. Stricture
• Stricture can be due to intrinsic or extrinsic causes
Intrinsic causes:
1. Long standing Central venous catheters
2. Transvenous pacemakers
3. Postoperative or post-radiation effects.
Extrinsic causes:
1. Malignancies (Most common)
2. Compression from mediastinal masses,
3. Fibrosing mediastinitis.

32. INTRINSIC EXTRINSIC

33. FIBRIN SHEATH
• A fibrin sheath is a heterogeneous
matrix of cells and debris containing
variable amounts of thrombus,
endothelial cells, and collagen that
forms around most hemodialysis
catheters by the end of the 1st week of
placement
• On Xray it can be seen as linear,
irregularly shaped, calcified or
noncalcified, structure within a central
vein

34. THROMBUS
• 2 types , either bland or tumour thrombus.
• Infection and thrombosis are the most common complications of long-
standing CVCs or implantable central venous devices.
• On Non enhanced CT – Difficult to identify.
• On Contrast enhanced CT- central or eccentric non enhancing filling defect
in the SVC, usually in relation to a CVC or pacer lead.
• Performing nonenhanced and gadolinium-enhanced MR imaging helps in
identifying bland thrombus. As opposed to bland thrombus, tumor
thrombus often shows heterogeneous contrast enhancement at MR
imaging
• Tumor thrombus is generally larger and lobulated and is associated with an
adjacent mass or wall invasion

36. TRAUMA
• RARE
• Mostly due to penetrating trauma
• It is usually seen at the junction of the
SVC and right atrium because of the
relative mobility at this hinge point and
results in a contained mediastinal
hematoma
• Hemopericardium with pericardial
tamponade physiology may be seen.

37. PRIMARY NEOPLASMS

38. To Summarise. . .
• SVC is an important and often ignored structure.
• This is best visualized on contrast enhanced CT .
• There are not many pathologies associated with SVC
but important one is the Persistent Left SVC which is an
incidental finding while doing post CVC X-Ray.
THANK YOU

39. References
• Sonavane SK, Milner DM, Singh SP, Abdel Aal AK, Shahir KS, Chaturvedi A.
Comprehensive Imaging Review of the Superior Vena Cava. Radiographics. 2015
Nov-Dec;35(7):1873-92.doi: 10.1148/rg.2015150056. Epub 2015 Oct 9. PMID:
26452112.
• Liu, Haitao & Li, Yahua & Wang, Yang & Yan, Lei & Zhou, Pengli & Han, Xinwei.
(2021). Percutaneous transluminal stenting for superior vena cava syndrome caused
by malignant tumors: a single-center retrospective study. Journal of Cardiothoracic
Surgery. 16. 10.1186/s13019-021-01418-w.
• Netter Atlas of Human Anatomy 7th Edition.
• Inderbir Singh’s Human Embryology 11th Edition.