How to evaluate lower extremity pseudoaneurysms on ultrasound
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:
- Measure the pseudoaneurysm sac using a transverse two-dimensional (2D) view.
- Turn on color Doppler and look for the yin-yang sign and neck.
- Measure the length and width of the neck.
- 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.
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.
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.
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.
Pseudoaneurysm treatment and follow-up
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.
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.
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.
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.
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.
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 normal. However, when a duplex ultrasound was performed in the right groin, a pseudoaneurysm was found with its characteristic yin-yang appearance and neck.
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