1. Correct Answer: C. Between the media and adventitia

Rationale: A pseudoaneurysm, also known as a false aneurysm, is a collection of blood that forms between two of the layers of an artery, whereas a true aneurysm involves all three layers of the arterial wall. They typically form between the media and adventitia following trauma to the vessel. Pseudoaneurysms most commonly involve the femoral artery following angiography. The presentation may vary from clinically silent to life-threatening emergencies. Symptoms depend on the size and location of the pseudoaneurysm. Pain is common and occurs from increased pressure from swelling or nerve compression. On clinical examination, a pulsatile mass may be palpable, associated with a thrill or murmur. Pseudoaneurysms may cause significant morbidity due to an increased risk of rupture, thromboembolism, extrinsic compression of nearby neurovascular structures, or necrosis of overlying skin and subcutaneous tissue. Risk factors for pseudoaneurysms include a lower femoral puncture site, larger sheath size, anticoagulation or antifibrinolytic therapy, older age, and arterial hypertension.

Ultrasound of pseudoaneurysms can reveal a pulsatile anechoic saccular lesion with variable echogenicity, depending on the presence of an intraluminal thrombus. When there is no thrombus, it is anechoic; when the pseudoaneurysm is completely thrombosed, it may be difficult to differentiate from a hematoma. Images can also reveal swirling or fluid-fluid levels within a pseudoaneurysm. Color Doppler imaging shows a bidirectional, turbulent, swirling blood-flow pattern known as the yin-yang sign.

1. Chun EJ. Ultrasonographic evaluation of complications related to transfemoral arterial procedures. Ultrasonography. 2018;37(2):164-173.

2. Correct Answer: D. A heterogeneous, predominantly hypoechoic area

Rationale: The ultrasound appearance of pseudoaneurysms is expected to be heterogeneous. The variable echogenicity represents fluctuations of bleeding and rebleeding from the arterial wall lesion (Figure 71.4). Prior to thrombus formation, pseudoaneurysms are hypoechoic because they are predominantly anechoic liquid blood. Color flow Doppler may reveal a pulsatile, turbulent flow. The pathognomonic sign for pseudoaneurysm is a to-and-fro waveform within the arterial lesion on spectral or color Doppler imaging, often referred to as the yin-yang sign.

1. Alerhand S, Apakama D, Nevel A, Nelson BP. Radial artery pseudoaneurysm diagnosed by point-of-care ultrasound five days after transradial catheterization: a case report. World J Emerg Med. 2018;9(3):223-226.

2. Rybyinski A. Sonography-guided interventional procedures. In: Kawamura D, Nolan T, eds. Abdomen and Superficial Structures. 4th ed. Wolters Kluwer; 2018:795-811.

3. Correct Answer: D. Bidirectional turbulent, swirling blood flow through the pseudoaneurysm

Rationale: The yin-yang sign seen with color Doppler ultrasound is a bidirectional, turbulent swirling, or fluid-fluid level within a pseudoaneurysm. This sign is commonly noted on large pseudoaneurysms that will partially thrombose, and blood may fill only part of the lesion.

The sign is created when blood on one side of an aneurysm or pseudoaneurysm travels toward the probe, and blood on the other side travels away from the probe in a turbulent pattern (Figure 71.5). Although this sign is helpful in differentiating aneurysms or pseudoaneurysms from hematomas, cysts, or solid masses, it is not solely associated with vascular abnormalities. Some neoplasms, such as solid and papillary epithelial neoplasms, may also demonstrate the “yin-yang sign.” Furthermore, the absence of this sign does not rule out a pseudoaneurysm.

1. Chun EJ. Ultrasonographic evaluation of complications related to transfemoral arterial procedures. Ultrasonography. 2018;37(2):164-173.

2. Helms WE. Vascular ultrasound. In: Klein J, Vinson EN, Brant WE, Helms CA, eds. Brant and Helms’ Fundamentals of Diagnostic Radiology. 5th ed. Wolters Kluwer; 2019:1252-1276.

3. Lupattelli T. The yin-yang sign. Radiology. 2006;238:1070-1071.

4. Correct Answer: A. Observation