Superior Vena Cava Syndrome Imaging
Updated: Apr 26, 2021
Author: Michael J Cumming, MD; Chief Editor: Kyung J Cho, MD, FACR, FSIR
Practice Essentials
Superior vena cava (SVC) syndrome (SVCS) is a constellation of symptoms that result from obstruction of the SVC (see the images from a single case, below). The superior vena cava (SVC) is formed in the upper middle part of the mediastinum by the junction of the brachiocephalic veins. It is 6-8 cm long and drains into the right atrium at approximately the level of the right mainstem bronchus. The azygous vein loops over the right mainstem bronchus and connects to the posterolateral wall of the SVC. The SVC lies in a relatively confined space and is surrounded by several lymph node groups that predispose it to compression, invasion, or involvement in inflammatory conditions.[1, 2, 3, 4, 5]
A CT scan of the chest is the initial test of choice to determine whether an obstruction is being caused by external compression or a thrombosis. Diagnosis of SVC thrombosis by CT includes lack of SVC enhancement; intraluminal filling defects or narrowing; and visualization of the collateral vessels. The modality of choice for SVCS is contrast-enhanced CT with multiple phase imaging. The SVC can be studied during routine contrast-enhanced chest CT.[2, 6, 7, 8, 9, 10]
SVCS is caused by compression, invasion, and/or thrombosis of the superior vena cava and/or the brachiocephalic veins.[3] Obstruction of blood flow in the SVC can be characterized by facial, neck, and upper extremity swelling; facial plethora; distended chest and neck veins; and cyanosis.[4]
Although some cases of SVCS are caused by nonmalignant conditions, such as thrombosis and fibrosing mediastinitis, thoracic malignancies have been reported to be responsible for 60-85% of cases.[4, 11, 12] The most frequent malignancies are bronchogenic carcinoma (in order of decreasing frequency: small cell carcinoma, squamous cell carcinoma, adenocarcinoma, large cell carcinoma), followed by non-Hodgkin lymphoma. Many other malignancies have been reported; essentially, any mediastinal mass may compress or invade the SVC.
Benign causes include central venous catheters (increasing in frequency), pacemaker wires, fibrosing mediastinitis, thoracic aortic aneurysms, and a multitude of unusual conditions.[13]
Superior vena cava syndrome (case 1). The patient was a 35-year-old man with a 3-year history of progressive upper-extremity and fascial swelling. The patient had undergone treatment for histoplasmosis in the past. CT scan shows a narrowed superior vena cava with adjacent calcified lymph nodes and posterior soft tissue thickening.
Superior vena cava syndrome (case 1, cont'd). Sonogram shows markedly damped venous waveform with complete loss of normal venous pulsatility and minimal respiratory variation.
Superior vena cava syndrome (case 1, cont'd). Venogram shows almost complete occlusion of the superior vena cava with dramatic collateral drainage through the left superior intercostal vein.
Superior vena cava syndrome (case 1, cont'd). A Palmaz P308 stent mounted on a 12-mm balloon was deployed in the superior vena cava after it was predilated to 8 mm. The stent was subsequently dilated to 14 mm.
Superior vena cava syndrome (case 1, cont'd). Venogram obtained after stenting shows a widely patent superior vena cava with no collateral drainage. Pressure measurements after stenting showed a 1- to 2-mm residual gradient.
Superior vena cava syndrome (case 1, cont'd). Sonogram obtained 1 year after stenting shows near-normal venous pulsatility and respiratory phasicity. The patient experienced a complete resolution of symptoms.
Imaging Modalities
The examination of a patient suspected of having superior vena cava syndrome depends on the patient's prior medical history. All patients should undergo chest radiography and Doppler ultrasonographic evaluation of the central veins. If normal venous waveforms are seen in the brachiocephalic, subclavian, and internal jugular veins, the presence of a significant SVC stenosis is unlikely.[14, 15, 6, 7, 2, 16, 17, 18, 13]
Radiographs
SVCS can neither be confirmed nor ruled out by radiographs, but radiographs may show masses or pleural effusions or indirect signs of pulmonary embolism. Plain radiographs are not recommended in emergency situations.[3] On frontal radiographs, the SVC forms an interface along the upper right mediastinal border that fades above the medial end of the clavicle. A widening of this interface suggests SVC dilatation or a mediastinal mass. A round or oval opacity at the right tracheobronchial angle marks the terminal portion of the azygos vein and is an important landmark for identifying malposition of a central line. An abnormal dilatation of the azygos can be a sign of central venous obstruction.[2]
CT and MRI
In patients with suspected malignancy, CT of the thorax should be performed.[19, 20, 1, 21] A CT scan of the chest is the initial test of choice to determine whether an obstruction is being caused by external compression or a thrombosis. CT can provide more accurate information regarding location of obstruction. In addition, it may help guide attempts at biopsy by mediastinoscopy, bronchoscopy, or percutaneous fine-needle aspiration, as well as provide information on other critical structures, such as the bronchi and the vocal cords.[2]
Diagnosis of SVC thrombosis by CT includes lack of SVC enhancement; intraluminal filling defects or narrowing; and visualization of the collateral vessels. Visualization of the collateral vessels has a reported sensitivity and specificity of 96% and 92%, respectively, for the diagnosis of SVC obstruction.[8, 9]
The modality of choice for SVCS is contrast-enhanced CT with multiple phase imaging. The SVC can be studied during routine contrast-enhanced chest CT. Sonovane et al noted that in their experience, contrast-enhanced CT performed 60-75 seconds after injection of a contrast agent into a peripheral vein achieved excellent uniform enhancement of the SVC. They also note that streak artifacts can be minimized by using diluted contrast material and vascular window settings (window level, 100 HU; window width, 600–700 HU), and that to minimize mixing artifacts, additional delayed acquisition at 60 seconds with limited z-axis coverage over the SVC is often useful when SVC thrombus is a clinical concern[2, 3]
Nonenhanced CT can demonstrate SVC duplication, narrowing, and enlargement; central venous catheter position; and calcifications along the SVC.[2]
Magnetic resonance venography may be used to image the central veins for patients with allergies to contrast material.[22] If the findings of noninvasive imaging studies are uncertain or if the clinical diagnosis of SVCS is uncertain, venography with contrast medium or carbon dioxide, as well as pressure measurements, are extremely useful. MR venography has been shown to be as sensitive and specific as conventional venography for central venous obstruction. Gadolinium-enhanced MR venography can include static high-resolution first-pass, time-resolved, or steady-state acquisitions.[2]
Ultrasound
The presence or absence of venous thrombosis must be determined. Acute onset or a change in symptoms suggests acute thrombosis. Ultrasonography is useful for excluding thrombus in the upper extremity, axillary, subclavian, and brachiocephalic veins in most patients. The SVC cannot be directly imaged because of the lack of an adequate acoustic window. SVC patency may be indirectly determined with normal waveforms in the subclavian and brachiocephalic veins.
Venography
Contrast-enhanced venography may be required to exclude central venous thrombosis when ultrasonographic findings are suboptimal or inconclusive. Transesophageal echocardiography may also be used to image the SVC and right atrium.[23]
Tissue diagnosis
Obtaining a tissue diagnosis is the first step in the treatment of patients with SVC syndrome (SVCS) caused by a mediastinal mass. The workup of patients varies according to the patient's age, medical history, and imaging findings. Mediastinal masses may be examined by means of percutaneous biopsy under CT guidance and, occasionally, under ultrasonographic guidance. In certain circumstances, mediastinoscopy is required. Large core samples are needed for patients with suspected lymphoma. Pleural effusions may be aspirated and sent for cytology.