Review: Body and Extremity Magnetic Resonance Venography
Key findings
- At Massachusetts General Hospital, most magnetic resonance venography (MRV) protocols employ both non-contrast and contrast-enhanced techniques; gadoterate meglumine (Dotarem®) is the most commonly used contrast medium
- Time-resolved MRV provides higher temporal resolution than single-phase contrast-enhanced MRV through rapid sequential imaging, but there's a trade-off between temporal and spatial resolution
- MRV is useful for evaluating conditions arising from venous compression: May–Thurner syndrome, nutcracker syndrome, and Paget-Schroetter syndrome (effort thrombosis), a rare venous form of thoracic outlet syndrome
- MRV is particularly useful for detecting tumor thrombus
Magnetic resonance venography (MRV) is increasingly used instead of, or in addition to, duplex ultrasound and computed tomography venography. It doesn't require ionizing radiation and can be performed without intravenous contrast, and recent technical advances have improved its sensitivity, image quality, and acquisition times.
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In Magnetic Resonance Imaging Clinics of North America, MRV experts at Massachusetts General Hospital recently reviewed commonly used body and extremity MRV techniques, clinical applications, and cases where off-label ferumoxytol can replace gadolinium.
The authors are Rory L. Cochran, MD, PhD, of the Division of Abdominal Imaging, Brian B. Ghoshhajra, MD, MBA of the Division of Cardiovascular Imaging in the Department of Radiology, and Sandeep S. Hedgire, MD, division chief of the Division of Cardiovascular Imaging.
Techniques
At Mass General, most MRV protocols combine non-contrast and contrast-enhanced (CE) techniques. Gadoterate meglumine (Dotarem®) is the contrast medium most commonly used. A table in the article provides a sample MRV protocol for the pelvis.
A relatively new technique, time-resolved MRV, provides higher temporal resolution than single-phase CE-MRV through rapid sequential imaging. A full-resolution non-contrast image is followed by multiple sequential incomplete acquisitions focusing on the center of k-space, so there is a trade-off between image contrast and spatial resolution.
Venous Compression Syndromes
The authors discuss the use of MRV to evaluate deep vein thrombosis, disorders of the inferior and superior vena cava, central venous stenosis, and pelvic venous congestion. They also describe the use of MRV to evaluate patients suspected of having venous compression syndromes:
May–Thurner syndrome is compression of the left common iliac vein between the right common iliac artery and the anterior aspect of the fifth lumbar vertebral body, resulting in ipsilateral deep vein thrombosis. MRV with time-of-flight (TOF) and CE sequences enables the evaluation of vessel patency, altered flow dynamics, and the severity of the syndrome.
MRV findings include focal narrowing of the left common iliac vein in the affected segment, reversal of flow on TOF images, and ipsilateral pelvic venous collaterals.
Nutcracker syndrome, which can be anterior or posterior, is compression of the left renal vein as it crosses the aorta before joining the inferior vena cava. MRV findings include focal narrowing of the left renal vein in the shape of a bird's beak, and this "beak sign" has high diagnostic sensitivity and specificity. Increasing angle acuity between the superior mesenteric artery and the aorta is also a useful diagnostic metric.
Other characteristic findings on MRV are ipsilateral retrograde gonadal vein flow on TOF images and pelvic varicosities and cross-pelvic collaterals on CE-MRV.
Paget-Schroettersyndrome (PSS), also called effort thrombosis, is a rare venous form of thoracic outlet syndrome (vTOS) in individuals who develop deep vein thrombosis of the axillary and subclavian veins. It results from dynamic compression of the subclavian vein as it exits the thoracic outlet through the costoclavicular space.
The typical patient is a young, athletic male with unilateral upper extremity pain, swelling and cyanosis after exercise. Intermittent subclavian vein compression with symptoms but no thrombosis is known as McCleery syndrome.
MRV findings of vTOS include dynamic subclavian vein narrowing with arm abduction, fixed stenosis at the site of dynamic narrowing, venous collaterals bypassing the stenotic segment, axillosubclavian vein thrombosis and aberrant anatomy (osseous and/or soft tissue). Venous compression alone at the costoclavicular space is not diagnostic because many patients without vTOS demonstrate focal compression.
Oncologic Applications of MRV
MRV is incredibly useful in distinguishing bland from tumor thrombus. This is particularly important in renal cell carcinoma and hepatocellular carcinoma, as a tumor in the vein influences staging and management of those diseases.
Features characteristic of a tumor in the vein are venous expansion (more prominent than observed with an acute bland thrombus), malignant thrombus that seems contiguous with the primary tumor, enhancement of the venous filling defect, and enhancement features resembling the primary tumor. When diffusion sequences are obtained, tumor thrombus often restricts diffusion, whereas bland thrombus usually does not.
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