How to evaluate lower extremity pseudoaneurysms on ultrasound

26th Feb 2021

Pseudoaneurysms are caused by a penetrating injury to the arterial wall. This causes blood to leak from the artery and pulsate into the surrounding tissues. 

One cause of a pseudoaneurysm is an iatrogenic puncture during catheterization. Suspect a pseudoaneurysm if a pulsatile groin mass appears after surgery involving groin catheterization. 

Thankfully, pseudoaneurysms are easily evaluated on ultrasound. Let’s take a look at how to examine, treat, and perform follow-ups for a pseudoaneurysm. 


How to examine and measure a pseudoaneurysm on ultrasound

Measurement of a pseudoaneurysm, similar to stents, follows a standard protocol:

  1. Measure the pseudoaneurysm sac using a transverse two-dimensional (2D) view.
  2. Turn on color Doppler and look for the yin-yang sign and neck.
  3. Measure the length and width of the neck.
  4. Capture Doppler waveforms at the neck.

Step 1: Measure the pseudoaneurysm using the transverse 2D view

In a transverse 2D view, measure the pseudoaneurysm from the outer wall to the opposite outer wall and note any thrombus. 

Pseudoaneurysm with a thrombus being measured on ultrasound from outer wall to outer wall. Ultrasound image.

Figure 1. Measure the pseudoaneurysm from the outer wall to the opposite outer wall using a transverse two-dimensional view and note any thrombus.

Step 2: Turn on color Doppler and look for the yin-yang sign and neck

The pseudoaneurysm’s appearance on color Doppler is referred to as the yin-yang sign. This represents the swirling flow of color from the blood jetting through the neck of the pseudoaneurysm. The leaking artery and the blood collection can be visualized on ultrasound. 

You can also visualize the pseudoaneurysm neck, which is the length of blood flow between an artery and a pseudoaneurysm sac.

Pseudoaneurysm sac on color Doppler with yin-yang appearance, neck, and leaking artery. Ultrasound image.

Figure 2. When examining a pseudoaneurysm on ultrasound, turn on color Doppler and look for the characteristic yin-yang sign of the pseudoaneurysm sac. As well, note the pseudoaneurysm neck and the leaking artery. 

Step 3: Measure the length and width of the neck

The pseudoaneurysm neck can vary in length and width, and occasionally there won’t be a discernable neck separating the pseudoaneurysm from the artery. When measuring the neck, keep in mind that the measurements are more accurate without color. This is because color can bleed over the edges of the vessel walls on the ultrasound screen. However, if the pseudoaneurysm neck is difficult to see without color, you may need to measure the neck with the color on. 

A pseudoaneurysm on black and white and color Doppler ultrasound. Image.

Figure 3. A pseudoaneurysm neck on duplex ultrasound is easier to see in the color Doppler mode than in the black and white mode.

Step 4: Capture Doppler waveforms at the neck

When assessing Doppler waveforms of the neck, the to-and-fro flow will be apparent on the waveforms since it pulses above and below the baseline.  

Doppler waveforms from a pseudoaneurysm neck. Ultrasound image.

Figure 4. The Doppler waveforms of a pseudoaneurysm neck demonstrate to-and-fro flow with waveforms above and below the baseline. 


Pseudoaneurysm treatment and follow-up

Watch-and-wait approach

The treatment of a pseudoaneurysm consists of a few options. If the pseudoaneurysm is not quickly expanding, a watch-and-wait approach with serial follow-up visits is appropriate. 

Twenty-minute compression

If it does not clot on its own, then a twenty-minute compression of the pseudoaneurysm neck can be performed with the ultrasound probe in an attempt to achieve thrombosis. This method is not frequently used because it causes pain for the patient, is strenuous for the ultrasound technologist, and is time-consuming. 

After this treatment, the common femoral artery should be examined for evidence of pseudoaneurysm clot extension.

Injection of thrombin

Another option is an injection of thrombin into the pseudoaneurysm sac. This is the preferred method to treat pseudoaneurysms because it is relatively fast, not as difficult for the operator, and not as uncomfortable for the patient. 

The injection of thrombin is ultrasound-guided, which helps confirm needle placement, visualize the injection, and ensure there is no clot extension into the native artery. Clot extension can cause an occlusion of the native artery (e.g., clot embolism) from the pseudoaneurysm sac into the legs. 


What to look for on follow-up ultrasounds of a pseudoaneurysm 

Pseudoaneurysms can clot on their own, which is why a watch-and-wait method is often a reasonable option. During this period, serial ultrasounds help track spontaneous thrombosis.  

On color flow duplex ultrasound, a partially thrombotic pseudoaneurysm will demonstrate diffuse blood flow within the thrombus. 

A partially thrombotic pseudoaneurysm on color flow duplex. Ultrasound image.

Figure 5. A partially thrombotic pseudoaneurysm demonstrating diffuse blood flow within the thrombus on color flow duplex ultrasound. 

When a pseudoaneurysm is mostly clotted, you can see varying gray tones in a 2D view which represent clotted blood. Any remaining active bleeding will show up as an anechoic (e.g., completely black) section. 

Mostly clotted pseudoaneurysm on two-dimensional ultrasound. Image.

Figure 6. This pseudoaneurysm is mostly clotted, as seen by varying gray tones representing clotted blood. The anechoic (e.g., completely black) section on the bottom is the remaining active bleeding.

Manual compression of the neck, or a thrombin injection into the pseudoaneurysm sac, speeds complete thrombosis of a pseudoaneurysm. With a fully thrombotic pseudoaneurysm, the pseudoaneurysm sac should show no flow, which can be confirmed by color Doppler. 

Fully thrombotic pseudoaneurysm on color flow duplex ultrasound. Image.

Figure 7. A fully thrombotic pseudoaneurysm shows no characteristic yin-yang flow on color Doppler and a fully patent artery.

After the successful treatment of a pseudoaneurysm, you should be able to compare the pre- and post-treatment images. To confirm a successful thrombosis, note that the pseudoaneurysm sac no longer has blood flow on examination with color Doppler. The thrombotic pseudoaneurysm is now referred to as a hematoma. 

The neck (if there still is one) should not show any to-and-fro flow. As well, its waveforms should only show pulses above the baseline. 

Pre- and post-treatment color flow and Doppler ultrasound images of a pseudoaneurysm.

Figure 8. Pre- and post-treatment images of a small pseudoaneurysm with a long neck after ultrasound-guided compression. The pre-treatment Doppler waveforms from the neck show pulses above and below the baseline; the post-treatment waveforms are all above the baseline. 


Case demonstrating a pseudoaneurysm found on duplex ultrasound after a normal ABI 

Remember, a patient with a pseudoaneurysm will have a normal ankle-brachial index (ABI). At first, an ABI report can be confusing to look through—but don’t let it intimidate you! Start by looking at the ABI calculations.

In this case, the patient’s ABI ratios were 1.25 for the right posterior tibial artery (PTA) and 1.18 for the dorsalis pedis artery (DPA), which are considered normalHowever, when a duplex ultrasound was performed in the right groin, a pseudoaneurysm was found with its characteristic yin-yang appearance and neck.  

Ankle-brachial index (ABI) report illustration showing normal ratios and duplex ultrasound images showing a pseudoaneurysm.

Figure 9. A patient case presenting with a pseudoaneurysm and normal ankle-brachial index (ABI) ratios. The pseudoaneurysm with its characteristic yin-yang appearance and neck was found on duplex ultrasound.

If you suspect a pseudoaneurysm, all you need is a duplex ultrasound! Medmastery note.

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