Nonvascular Findings Encountered During Venous Sonography

Introduction

It is not unusual to encounter incidental findings during the course of a venous examination. Some of these findings may be the cause of extremity pain or swelling apart from venous disease. Recognition of the sonographic features associated with different pathologies is critical for accurate diagnosis. Many of these diagnoses are common, such as edema, hematoma, lymph nodes, or popliteal (Baker) cysts. Other findings are less common, but no less important, including abscess, joint effusion, adenopathy, benign or malignant tumor, and metastatic disease.

It is always important to discuss severity, timing, and location of pain and/or swelling with the patient during the study. Be sure to examine the areas of concern in addition to your standard protocol views. Not only does this improve your detection of important findings, it also allows your patient an opportunity to describe the reason for their visit.

Soft Tissue Edema

Lower extremity edema is a common cause of limb swelling and is associated with either elevated venous pressures or lymphatic obstruction (lymphedema), or both. Causes of increased hydrostatic pressure within the venous system include heart failure (HF; venous congestion), fluid overload, deep vein thrombosis (DVT), venous compression, and other causes of venous obstruction. These problems result in leg swelling and soft tissue edema.

There is a change in venous flow patterns in cases of heart failure. We expect to see phasic, nonpulsatile waveforms in the normal lower extremity veins. In right-sided heart failure, the waveforms are usually more pulsatile and typically bidirectional, with components seen above and below the baseline ( Fig. 22.1 ). As noted in Chapter 1 , causes of increased venous pressure such as heart failure or tricuspid insufficiency lead to increased transmission of cardiac phasic changes in pressure and blood flow to the peripheral veins of the upper and lower limbs. These changes result in increased pulsatility in the peripheral vein waveforms. Pulsatility in the venous system may resemble arterial pulsations because of the bidirectional pattern of blood flow. Comparison of the arterial and venous flow patterns is key to distinguishing pulsatile venous signals from arterial flow. On close inspection, the phases of the venous pattern are less periodic than the typical triphasic waveforms found in the arterial system. Other clues to the nature of the flow abnormality are the direction of flow and the communications with the superficial veins. Another distinguishing characteristic is the change in venous flow that occurs with the Valsalva maneuver. This does not occur on the arterial side.

Pulsatile venous waveforms from venous congestion are frequently mistaken for signals associated with arteriovenous fistula (AVF). Although blood flow patterns seen with both venous congestion and AVF will demonstrate increased pulsatility, there are major differences. The waveforms identified from both the arterial and venous sides of an AVF will show an arterialized pattern with a low-resistance (high-diastolic) component. Blood flow in the fistula will only be in one direction toward the venous or lower-pressure side without reversal of flow. This is very different from the typical biphasic (above and below the baseline) pattern seen with venous congestion.

Gray-scale imaging may show a marbled, reticulated pattern when edema collects in the subcutaneous fat. Small collections of fluid may be seen when edema collects in the superficial tissues ( Fig. 22.2 ) and can be associated with significant soft tissue swelling. Attenuation of sound may occur that can restrict visualization of deep tissues and underlying vascular structures. A sound approach to this problem is to switch transducers to allow lower-frequency imaging. Changing from the usual 5 to 7 MHz linear array probe to a 2 to 5 MHz curved array transducer should allow deeper penetration of sound and improved visualization of the deeper areas of interest.

Bilateral leg swelling is a typical presentation for patients with venous congestion. It is also a common indication for venous sonography. Studies have shown that the likelihood of identifying DVT in patients with bilateral leg swelling without significant risk factors is low (≤5%). Conversely, Naidich and associates showed that 23% of patients with bilateral symptoms and risk factors had underlying DVT. In this group, 78% of patients had risk factors for DVT. DVT cannot be reliably diagnosed or excluded on clinical grounds alone.

Venous compression and venous obstruction are also causes of leg swelling and edema. The unexplained presence of edema, in association with abnormal waveforms should prompt an investigation of the proximal (or central) venous structures for thrombosis or compression.

Unlike the increased pulsatility seen with increased venous pressures and venous congestion, decreased phasicity is noted with venous obstruction or compression ( Fig. 22.3 ). Causes of central venous thrombosis include inferior vena cava and iliac vein DVT. Venous compression may be caused by lymphadenopathy, metastatic tumor, aneurysm, fluid collection, pelvic mass, gravid uterus, and an overdistended bladder.

Lymphedema

Lymphedema is also associated with leg swelling and can mimic DVT. Obstruction of the lymphatics due to malignancy, trauma, or surgery will cause extremity swelling and pain. Patients will typically present with unilateral or bilateral leg swelling. The appearance of lymphedema is indistinguishable from soft tissue edema associated with venous congestion. There may or may not be lymph node enlargement to suggest the etiology of the leg swelling.