Imaging Diagnosis of Venous TOS
When a doctor suspects the diagnosis of venous TOS on clinical examination, he or she will order imaging tests. The imaging diagnosis of venous TOS is quick and accurate. In general, ultrasound, venography, CT venography, or MR venography can confirm the presence of a blood clot. Each of these tests has advantages and disadvantages.
A physician should initially make the presumptive diagnosis of venous TOS based on its dramatic presentation. Typically, one arm appears swollen and blue, and appears quite different from the other arm. In addition, in most cases, the patient notes an abrupt onset of these symptoms. Together with the clinical presentation, the physician can find edema, cyanosis and collateral veins on physical examination. Unfortunately, in most cases, a doctor cannot directly demonstrate the underlying blood clot.
Therefore, after the physician makes the initial diagnosis of venous TOS, imaging diagnosis of venous TOS serves several purposes. Firstly, imaging tests confirm the presence and extent of venous blood clot. Secondly, imaging tests clarify the extrinsic structures compressing the vein. Thirdly, imaging tests show the intrinsic damage to the vein. It is important to realize that arm motion forwards or over the head causes vein compression in many people. Therefore, experts perform imaging tests with the arms down and with the arms elevated.
Some specialists have suggested that hypercoagulable blood, or ‘thick’ blood that clots easily, causes venous TOS. For this reason, some physicians will obtain blood clotting tests in patients with venous TOS. At this time, there is little data to support routine testing of blood clotting factors. However, in patients with other clinical evidence of a blood clotting disorder, the physician may consider blood testing.
It is important to bear in mind that venous TOS frequently recurs following treatment. Therefore, many physicians perform routine follow-up imaging for early detection of recurrent stenosis or blood clot.
Imaging diagnosis of venous TOS
While there are several tests that doctors use to diagnose venous TOS, each has its advantages and disadvantages. Treatment of venous TOS has evolved significantly, although debate continues regarding optimal treatment methods and timing. Nonetheless, if a doctor diagnoses and treats venous TOS promptly, treatment outcomes are usually excellent.
X-rays show excellent bone detail, but do not show soft tissue detail, and are limited to two dimensions. X-rays do not show arteries or veins, and are almost always normal in patients with venous TOS. In addition, venous TOS is likely to occur without cervical rib or other bone anomaly. Therefore, x-rays have no significant diagnostic or therapeutic value in patients with venous TOS.
Direct venography produces excellent images of the subclavian vein on one side. In detail, the physician inserts a small catheter into a hand or arm vein and injects dye into the vein. During the injection, the physician takes X-ray images as the dye passes through the veins towards the heart. Direct venography provides two major advantages besides confirming the presence of a clot. Firstly, a physician can perform thrombolysis, injection of a clot-dissolving medicine, directly after the venogram. Additionally, the physician can perform venoplasty, dilating a venous stenosis with a balloon, directly after the venogram. Notably, direct venography can examine only one side at a time, and utilizes a moderate radiation dose. As a result, a physician would need to perform two separate procedures in patients with bilateral symptoms. Significantly, direct venography can provide excellent information in patients with surgically-altered anatomy, including dialysis fistula or graft. CT venography or MR venography demonstrate structures that cause compression of the vein, which can be valuable for planning surgery.
Ultrasound is performed without any radiation, and demonstrates blood flow in the veins in real time. This allows ultrasound evaluation during dynamic movement of the arms. At the same time, bones interfere with ultrasound and create blind spots. Thus, ultrasound may not directly demonstrate venous compression in the thoracic outlet. However, ultrasound shows blood clots quite well, as well as abnormal venous waveforms just beyond the blind spot. Ultrasound does not demonstrate fibrous bands and muscle anomalies in detail.
CT venography (CTV) is performed by injecting contrast into a peripheral vein, without an arterial catheter. CTA is fast, and shows excellent detail of bones and arteries. However, CT venography does not show soft tissues in detail, including fibrous bands and muscle anomalies. Additionally, the patient receives a significant radiation dose during a CTV. In many centers, CTV is the first-line test for many vascular surgeons.
MR venography (MRV) can be performed in two ways. First is direct MRV. The physician injects contrast into a small arm vein. Shortly thereafter, the MRI scanner creates images as the contrast passes through the arm and chest. Direct MRV shows only veins, and only in one arm. In contrast is indirect MRV. Again, the physician injects contrast into a small arm vein. In contrast to direct MRV, scanning begins after a delay. First, injected contrast travels through the heart, the lungs, the arms, and returns through the arm veins. At this time, the MRI scanner creates images, showing both arteries and veins, in both arms. MRV shows the veins while eliminating other structures. MRV requires no radiation. If used in conjunction with MRI, superb soft tissue detail is available. Excellent depiction of fibrous bands, muscle anomalies, bones, and brachial plexus is possible with the combination of MRV and MRI.
This patient had an MR angiogram, followed by an MR venogram. Slide the handle side to side to see the difference between the two studies.
Treatment of Venous TOS
Primary treatment is performed by urgent treatment of the venous blood clot. Following this, structures that compress the vein are often reduced or removed, and repair of the vein is performed if it is damaged. Learn more about the treatment of venous TOS here.