The Institute for Advanced Medical Education is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.

The Institute for Advanced Medical Education designates this educational activity for a maximum of 1 AMA PRA Category 1 Credit(s) TM. Physicians should only claim credit commensurate with the extent of their participation in the activity.

These credits are accepted by the American Registry for Diagnostic Medical Sonography (ARDMS).

Faculty: Joseph F. Polak, MD, MPH;Director of Cardiovbascular Imaging, New England Medical Center , Boston MA with the assistance of: Jean M. Alessi-Chinetti, RVT, RDMS Technical Director Vascular Diagnostoic Laboratory, Brigham and Women's Hospital, Boston MA

Course: Peripheral Arterial Studies: Non-Atherosclerotic Pathologies

Topics presented in this presentation are discussed in more detail in the following textbook: Peripheral Vascular Sonography.  2nd edition.  by Joseph F. Polak   Lippincott, Williams and Wilkins 2004

Target Audience: Physicians, sonographers and others who perform and/or interpret vascular ultrasound.

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For any questions or problems concerning this program or for problems related to the printing of the certifcate, please contact IAME at 914-921-5700 or email us. .

Estimated Time for Completion of tutorial: approximately 50 minutes Date of Release and Review: June 30, 2008
Expiration Date: June 30, 2011

Disclosure: In compliance with the Essentials and Standards of the ACCME, the author of this CME tutorial is required to disclose any significant financial or other relationships they may have with the manufacturer(s) of any commercial product(s) or provider(s) of any commercial service(s) discussed in this program.

Dr. Joseph F. Polak and Jean M. Alessi-Chinetti, RVT, RDMS have indicated that no such relationships exist.

IAME discloses no relevant financial relationships with commercial interests. 

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Peripheral Arterial Studies: Non-Atherosclerotic Pathologies

Joseph F. Polak, MD, MPH
Director of Cardiovbascular Imaging,
New England Medical Center,
Boston MA
with the assistance of:
Jean M. Alessi-Chinetti, RVT, RDMS
Technical Director
Vascular Diagnostoic laboratory,
Brigham and Women's Hospital,
Boston MA

(DIRECT TO QUIZ)

Objectives

After completing this course, the participant should be able:

• to describe an arterio-venous (A-V) fistula
• to describe the typical waveform of a pseudoaneurysm
• to discuss the ultrasound evaluation of dialysis access fistula or grafts
• to discuss the differential diagnosis of palpable masses in close proximity to arteries

Introduction

Doppler sonography and color Doppler imaging can be used to accurately diagnose the presence of native arterial lesions and stenoses developing in bypass grafts. Doppler sonography also serves broader diagnostic needs by permitting the diagnosis of a broad range of pathologies not directly related to atherosclerosis. Doppler ultrasound offers the ability to document the presence or absence of blood flow within masses located in close proximity to vessels. The clinical request for an arterial Doppler evaluation often comes in a patient with recent trauma or following an arterial catheterization. Many patients present with an unexpected clinical finding, typically the presence of a pulsatile mass. Another scenario is the presence of a bruit detected during a clinical examination. Finally, a dialysis access grafts or access fistula showing clinical evidence of poor function can be easily evaluated with Doppler ultrasound.

The following paragraphs review some of the findings that can be seen when Doppler ultrasound is used to evaluate patients with this broad range of clinical presentations.

Arterio-Venous (A-V) fistula

A fistulous communication will occasionally occur following cardiac catheterization or any other angiographic procedures. This pathology can be quickly detected using color Doppler imaging (figure 1). The fistula causes elevated blood flow velocities in the communicating channel. This causes soft tissue vibrations detected as broad color Doppler signals in the surrounding soft tissues. Setting the color Doppler velocity scale to a high value helps in using the color Doppler image to delineate the site of the fistulous communication between vein and artery. The recipient vein has abnormal Doppler waveforms with spectral broadening (broad differences in the direction of blood flow) and an irregular contour (turbulence) to the Doppler waveform envelope (figure 2). The fistula will most often enter the common femoral or profunda femoral vein (figure 1). Doppler waveform analysis can sometimes show an arterialized appearance (figure 2).

		Figure 1: This color Doppler image clearly shows a communication between the profunda femoral artery (PFA, in red) and the profunda femoral vein (PFV, in blue). The area of high frequency signals identifies the location of the fistula (arrow). The ability to identify such a communication is dependent on the Doppler technique used. A high velocity scale (or PRF, peak repetition frequency) is required. To view an enlargement, click on the image.
		Figure 2: The Doppler tracing within the communicating channel will show a broad mixture of background frequencies (the hissing sound heard on the audio component of the Doppler signal). The arterial waveforms are discernible on the tracing since the Doppler gate was placed over the fistula communication. Turbulence is discernable as a shaggy contour to the waveform during systole. To view an enlargement, click on the image.

The communicating channel seen on color Doppler imaging is impossible to localize on gray scale images alone. If only waveform analysis is done, the Doppler gate must be moved throughout the soft tissues since the channel is typically small and can easily be missed. The arterialized signals will typically be seen in the communicating channel itself or in the efferent vein close to the entry site of the fistula (figure 3). The inflow artery can show a low resistance pattern due to the low resistance outflow through the fistula into the vein. The bigger the size of the fistula, the more diastolic flow is seen. The arterial waveform distal to the level of the fistula regains a more typical appearance. The communicating channel and the vein close to the channel show an arterialized signal and a broad frequency range of signals (figure 2).

Figure 3: The typical effect of an arterio-venous fistula on the Doppler tracings is shown on this diagram. The inflow artery can show a low resistance pattern due to the low resistance outflow into the vein. The bigger the effective fistula, the more diastolic flow is seen. The arterial waveform distal to the fistula regains a more typical appearance. The communicating channel and the vein close to the channel show an arterialized signal and a broad frequency range of signals (figure 2). To view an enlargement, click on the image.

The communicating channel is best discernable when the Doppler velocity scale is set to a high velocity setting (figure 2). An indirect sign of the hemodynamic significance of an arterio-venous fistula is persistence of blood flow pattern in the efferent vein during a Valsalva maneuver. In a normal vein, a Valsalva maneuver should stop returning venous blood flow completely. The raised intra-abdominal pressure impedes venous return and blood flow ceases.

Figure 4: This figure shows a Doppler tracing of the common femoral vein (transverse) while a Valsalva maneuver is being performed. During the "hold" of the Valsalva, blood flow continues. The blood flow signals have an arterial appearance. This is an indication of a relatively large arterio-venous fistula. Sampling of the Doppler waveform during the Valsalva maneuver should be done as close as possible to the site of the fistula. To view an enlargement, click on the image.

With small A-V communications, the venous velocity signals can easily decrease during the Valsalva maneuver. Complete abolition of the flow signals during the Valsalva maneuver suggests that the fistula is likely to spontaneously occlude over the next two to three weeks.

Transcutaneous therapy aimed at achieving closure of the fistula as been described using ultrasound monitoring and by applying pressure over the fistula for periods of 20 to 60 minutes. Success rates of transcutaneous repair attempts are 30% or lower. This approach has been abandoned and either surgery or percutaneous closure is now typically done.

A perceived bruit on physical examination can also be caused by an arterial stenosis and the increased blood flow velocities associated with it. In addition, the use of percutaneous closure devices has increased the likelihood that the device can migrate and cause a stenosis by obstructing the arterial lumen (figure 5). These entities are part of the differential diagnosis and care should be given to carefully examine the native artery for the presence of such abnormalities.

		Figure 5: This gray scale image shows the remnant of a femoral puncture site into the common femoral artery (black arrow). Evidence of a "closure device" is seen as an echogenic structure abutting the near wall (white arrow). Closure devices can migrate into the artery lumen and cause a stenosis. To view an enlargement, click on the image.

A pseudoaneurysm is a complete rupture through the three walls of the artery. The intima, media and adventitia are compromised. In the lower extremity, the escaping blood pools as a well circumscribed mass and is constrained by the surrounding soft tissues. Pseudoaneurysms can develop following penetrating trauma or arterial catheterization. The communicating channel between pseudoaneurysm and arterial lumen is detectable by color Doppler imaging. Often, a high velocity scale (PRF, peak repetition frequency) is needed since blood flow velocities are very high.

The presence of a "to-and-fro" or "forward-backward" waveform is typically seen when the Doppler gate is placed over the communicating channel of the pseudoaneurysm (figure 6 and 7). The "to" or "forward" component is due to entry of blood into the collection as the soft tissues expand to accommodate entry of blood within the pseudoaneurysm cavity. This occurs during systole. The "fro" or "backward" component is seen during diastole as the blood stored in the cavity is ejected back into the artery. This is caused by the stored energy due to the elasticity of the surrounding soft tissues. Pseudoaneurysms can have multiple compartments as well as be solitary . Blood flow in a pseudoaneurysm cavity has a tendency to show a swirling pattern (figure 8).

Figure 6: The presence of a "to-and-fro" or "forward-backward" waveform is typically seen when the Doppler gate is placed over the communicating channel of the pseudoaneurysm. The "to" or "forward" component is due to entry of blood into the collection as the soft tissues expand to accommodate entry of blood within the pseudoaneurysm cavity. This occurs during systole. The "fro" or "backward" component is seen during diastole as the blood stored in the cavity is ejected back into the artery. This is caused by the stored energy due to the elasticity of the surrounding soft tissues. Pseudoaneurysms can have multiple compartments as well as be solitary. To view an enlargement, click on the image.

		Figure 7: This Doppler tracing is obtained from the communicating channel (sometimes call a neck) of the pseudoaneurysm. The forward and backward pattern of blood flow is clearly depicted. This image should be considered essential to confirming the presence of a pseudoaneurysm. To view an enlargement, click on the image.
		Figure 8: This color Doppler image shows a typical pseudoaneurysm. Blood flow in the pseudoaneurysm cavity has a swirling characteristic. The communicating channel (arrow) can be seen at its base. To view an enlargement, click on the image.

The Doppler tracing obtained from the communicating channel (sometimes called the neck) of the pseudoaneurysm should clearly depict a forward and backward pattern of blood flow. An image demonstrating this waveform should be considered essential to confirming the presence of a pseudoaneurysm (figure 7).

Once considered a relative medical emergency, the management of pseudoaneurysms has significantly been affected by the wide use of sonography. The natural history of pseudoaneurysms is often a benign one. Thrombosis of the patients' pseudoaneurysms commonly occurs spontaneously. Fellmeth et al. first described the use of transcutaneous repair of pseudoaneurysms following catheterization. They described a simple protocol of applying pressure with the ultrasound probe over the neck of the pseudoaneurysm. The probe was kept along the long axis of the artery as flow into the cavity was obliterated: a sequence of up to three applications, each lasting 10 to 20 minutes, was used. Transcutaneous therapy was successful in more than 80% of cases. There is increased difficulty of performing transcutaneous compression repairs when the patient is anticoagulated. The likelihood of success is better for smaller pseudoaneurysms and those with longer communicating channels. Pseudoaneurysms arising from other arteries, the axillary or the brachial aarteries have also successfully treated by transcutaneous compression repair.

The use of ultrasound directed injection of thrombin (1000 units in 1 cc or 1000 Units diluted in 20 ml of saline) has also been shown to be effective in successfully treating pseudoaneurysms. This approach has been adopted by most centers despite the fact that it is not an FDA recognized use of thrombin. Continuing experience shows that the technique is superior to that of compression ultrasound (figure 9). It has replaced compression ultrasound as a simple percutaneous treatment. The only pitfalls are inadvertent injection of the thrombin in the wrong location and possible allergic reactions. The inadvertent injections are unlikely when ultrasound guidance is used to place the needle tip in the pseudoaneurysm cavity and not in either the neck or the native artery.

Figure 9: This Doppler waveform is obtained from within a pseudonaeurysm cavity immediately following the administration of thrombin. The Doppler tracing shows a high resistance pattern as the flow signals are still inpart transmitted through the solidifying pseudoaneurysm. Such a tracing can also be obtained fro the communicating channel. These are transmitted pulsations from the contiguous artery rather than actual blood flow into the pseudoaneurysm cavity. To view an enlargement, click on the image.

Dialysis access fistula or grafts

Evaluation of the status of a dialysis fistula or graft is increasingly being requested, especially in centers where dialysis is performed. There are various types of dialysis access communications.

The native artery to vein anastomosis, typically done between radial artery and distal cephalic vein (Brescia-Cimino), has regained popularity over the use of synthetic loop grafts. The communication is between the radial artery and a superficial vein. This type of dialysis access is quite durable. Typically, as the recipient vein becomes arterialized, it dilates and becomes suitable for the insertion of needles needed for dialysis.

Loop grafts typically placed from the brachial artery to basilic or cephalic veins. The grafts are mostly synthetic (polytetrafluoroethylene; PTFE) or made of autologous vein. Problems common to both types of dialysis access include the development of aneurysms, peri-graft hematomas (figure 10) or stenoses in the conduit or at the anastomoses. Stenotic lesions are more commonly seen at the venous outflow of PTFE grafts or at the arterial anastomosis. Stenotic lesions within the synthetic graft conduit are uncommon.

		Figure 10a: The patient with this synthetic dialysis access graft presented with acute local swelling over the dialysis access graft. The differential diagnosis includes a hematoma or a rupture of the graft with pseudoaneurysm formation. Color Doppler imaging is a simple way of differentiating between the two possibilities. Here, there is evidence of a large hematoma (white arrows) surrounding the access graft (color channel). This makes insertion of the needles needed to perform dialysis very difficult. To view an enlargement, click on the image.
		Figure 10b: This native vein access fistula has developed a partly thrombosed pseudoaneurysm (small arrows). The vein lumen is to the side (large arrow). To view an enlargement, click on the image.

Duplex sonography can be used to detect stenoses: the accuracy of the technique is estimated at 90%. The loss in specificity can be explained by turbulent flow patterns set up within venous access fistulas. The diagnostic accuracy is improved in straight segment grafts to the efferent veins, where the accuracy increases to 95%.

Peak-systolic velocities in well functioning dialysis access grafts are typically above 100 to 200 cm/sec (figure 11), tending to be higher in the first 6 months after graft placement or shunt creation. Superimposed stenosis can therefore be difficult to detect given the high baseline velocities. The length of the graft or fistula must be examined with color Doppler imaging in order to insure detection of any significant stenoses. An area of increased blood flow velocity of 100% (velocity ratio of 2 or more) is considered to be consistent with a high grade stenoses. Color flow and gray scale images are also useful for confirming the presence of an anatomic lesion. Stenotic lesions tend to develop on the venous side of the access fistula in more than 80% of cases. Occasionally, the stenosis can be at the level of the subclavian vein, specifically in individuals who have had temporary hemodialysis access with indwelling large diameter catheters. Low flow states of 50 cm/sec or less are indicative of the presence of high-grade stenoses.

Figure 11: A typical dialysis access graft has blood flow velocities above 100 to 200 cm/sec. The double echogenic lines (white arrows) identifies this dialysis access channel as a PTFE graft. To view an enlargement, click on the image.

Lymph nodes and other masses

Although the patient that presents with a palpable mass might give a history of acute onset of the abnormality, the source is often a sub-acute and sometimes chronic abnormality. The differential diagnosis of palpable masses in close proximity to arteries is a wide one.

The possible etiologies include lymph nodes, lipomas, ganglia and rarely neoplasms.

Lymph nodes will have a typical kidney bean appearance with inflow artery and outflow vein arising from the center. Malignancy in a lymph node will normally distort the anatomy of the node, making the contour less regular often with loss of the well defined echogenic central portion of the node. Inflammatory or hyperplastic nodes can sometimes reach quite large sizes but tend to keep the normal nodal architecture. Lymph nodes show a cluster of color Doppler signals at the level of the hilum where the artery and vein exit and enter the node (figure 13). An echogenic central portion is typically seen. The contour of the node if regular and without irregular lobulations suggests a benign nature. An hyperplastic lymph node can contain strong arterial and venous signals (figure 14). The nodes can sometimes be mistaken for a pseudoaneurysm. The Doppler waveform from hyperplastic nodes will not show the typical to-and-fro waveform of the pseudoaneurysm and should be easily distinguished when

Lipomas are hypovascular and tend to be small in size. Their echogenic texture tends to be even and typically echodense and they are avascular. Ganglion cysts are also avascular and will normally be seen in close proximity to a joint (figure 15). They can present as a pulsatile mass since the arterial pulsations are transmitted from an artery that lies in close proximity.

		Figure 12a: The typical blood flow velocity in a dialysis access is in the 200 cm/sec range. This dialysis access fistula shows a decreased blood flow velocity (less than 100cm/sec). The waveform has a typical appearance, showing evidence of turbulence as witnessed by the shaggy contour of the waveform. Turbulence is manifest by a random fluctuation of the peaks seen in the spectral tracing from millisecond to millisecond. This accounts for the rough and shaggy contour of the Doppler spectral envelope. To view an enlargement, click on the image.
		Figure 12b: The reason for the decreased blood flow velocities in this fistula is the presence of a stenosis. This is associated with a bruit and a perceived "thrill" on physical examination. This is different from the expected "thrill" normally felt near to the arterial anastomosis within the vein. The thrill associated with the stenosis is felt higher up in the arm, in the outflow portion of the vein. To view an enlargement, click on the image.

		Figure 13: This enlarged lymph node shows a cluster of color Doppler signals at the level of its hilum. The echogenic central portion is not clearly delineated on this transverse projection. The contour of the node is regular and without irregular lobulations that are seen with malignancies. This hyperplastic node can, on occasion, be mistaken for a pseudoaneurysm. To view an enlargement, click on the image.
		Figure 14: The Doppler tracing obtained from the base of the node shows a typical low resistance waveform typical of an hyperplastic node. This patient had chronic cellulitis of the lower leg, accounting for the development of the enlarged draining node. Such a tracing confirms that this is not a pseudoaneurysm. Lipomas are hypovascular and tend to be small in size. The echogenic texture tends to be even and typically echodense and are avascular. Ganglion cysts are also avascular and will normally be seen in close proximity to a joint. They can present as a pulsatile mass since the arterial pulsations are transmitted from an artery that lies in close proximity. To view an enlargement, click on the image.
		Figure 15: This echolucent mass (arrows) displaces the radial artery superiorly. The patient presented with a pulsatile mass. This echolucent mass seen at the wrist is a ganglion cyst that displaces the radial artery superiorly. Ganglion cysts are a rare cause of a pulsatile mass at the wrist. A more common cause is that of a pseudoaneurysm developing following radial artery catheterization. To view an enlargement, click on the image.

Baker's cysts are typically located behind the knee and are hypoechoic. They are hypovascular although pannus formation in Rheumatoid Arthritis can also show areas of increased blood flow on color Doppler imaging. Various soft tissue neoplasms such as sarcomas, are rarely detected on ultrasound imaging. Color Doppler imaging of malignant lymph nodes and vascular tumors will often show central areas of arterial flow (figure 16). Abscess formation is typically accompanied by more peripherally located areas of increased vascularity. Neovascularity is typically seen at the level of the capsule that forms around the infected collection. Sub-acute hematomas may also be associated with a capsule that has evidence of increased arterial blood flow signals.

Figure 16: This hypoechoic mass lies behind the knee in a location that is typical of that of a Baker's (synovial) cyst. However, the mass contains areas of neovascularity and has well defined arterial branches. This excludes a Baker's cyst from the diagnosis. Although pannus formation can have areas of increased blood flow similar to what is seen her, the knee joint is devoid of any such changes. This mass is a relatively vascular sarcoma that has developed behind the patients' knee. An abscess is also unlikely since the areas of vascularity are in the center of the mass and not at the periphery. To view an enlargement, click on the image.

Summary

Doppler sonography is a versatile imaging approach for evaluating a wide range of pathologies associated with the arterial system. This diagnostic use extends beyond the traditional evaluation of peripheral arterial disease due to atherosclerosis. The use of this non-invasive technique extends beyond the simple diagnosis of suspected arterial stenoses and occlusions.

Reference List

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