Arterial · IR Playbook

Ultrasound-Guided Thrombin Injection for Pseudoaneurysm (USG guided thrombin inj)

Ultrasound-guided thrombin injection is a minimally invasive treatment for an iatrogenic peripheral arterial pseudoaneurysm, most commonly arising from the common femoral artery after catheterization. Thrombin injected directly into the pseudoaneurysm sac converts fibrinogen to fibrin and usually produces thrombosis within seconds. Reported technical success is approximately 94–99%, with serious complications in about 1%, principally thrombin escape causing native-artery thrombosis or distal embolization.

Learning objectives

• Confirm pseudoaneurysm anatomy and distinguish it from hematoma, arteriovenous fistula and active uncontrolled bleeding.
• Select pseudoaneurysms suitable for direct thrombin injection and recognize lesions requiring surgical or endovascular treatment.
• Perform low-dose, endpoint-driven thrombin injection while continuously visualizing the needle tip and native artery.
• Recognize and manage distal embolization, native-artery thrombosis, venous thrombosis, recurrence and hypersensitivity reactions.

Indications

• Symptomatic iatrogenic peripheral arterial pseudoaneurysm causing pain, tenderness or an enlarging pulsatile swelling.
• Persistent pseudoaneurysm approximately ≥2 cm, particularly when spontaneous thrombosis is unlikely.
• Pseudoaneurysm enlarging on serial duplex ultrasound.
• Pseudoaneurysm persisting despite observation or ultrasound-guided compression.
• Pseudoaneurysm in a patient receiving anticoagulant or antiplatelet therapy, in whom compression is less likely to succeed.
• Selected femoral, brachial, radial or other superficial peripheral pseudoaneurysms with a clearly visualized sac, neck and parent vessel.

Absolute contraindications

• Known hypersensitivity to the selected thrombin preparation or, for bovine thrombin, known antibodies or severe hypersensitivity to bovine products.
• Active infection involving the pseudoaneurysm or overlying soft tissues.
• Rupture with hemodynamic instability, uncontrolled hemorrhage, threatened skin, compartment syndrome, distal ischemia or progressive neurologic compression requiring urgent surgical or endovascular repair.
• Inability to continuously visualize the pseudoaneurysm sac, neck, parent artery and needle tip with ultrasound.

Relative contraindications

• Very short or wide pseudoaneurysm neck because thrombin can escape into the parent artery.
• Associated arteriovenous fistula because thrombin may enter the venous circulation and cause venous thrombosis or pulmonary embolism.
• Large pseudoaneurysm, particularly ≥6 cm, because repeat injection or endovascular or surgical treatment may be required.
• Pseudoaneurysm arising from a small distal artery with limited collateral supply.
• Multiloculated pseudoaneurysm with poorly communicating chambers.
• Severe coagulopathy or thrombocytopenia that may reduce durable thrombosis.

Equipment

• High-resolution ultrasound unit with 5–12 MHz linear transducer, color Doppler and spectral Doppler capability.
• Sterile ultrasound probe cover, sterile gel, skin preparation solution, drapes and gloves.
• 21–25 G needle; a 22 G spinal needle is commonly used for a deep femoral pseudoaneurysm.
• 1 mL Luer-lock syringes for controlled low-volume injection.
• Thrombin preparation reconstituted according to manufacturer instructions, commonly to 1000 IU/mL.
• 1% lidocaine with a 25 G needle for local anesthesia.
• Normal saline, gauze and dressing materials.
• Resuscitation equipment and drugs for anaphylaxis, including intramuscular adrenaline.
• Immediate access to heparin, angiography, aspiration thrombectomy or surgical support for arterial thromboembolic complications.

Procedure steps

1. Perform complete duplex examination of the pseudoaneurysm, parent artery and adjacent vein. Measure the sac and neck, identify all chambers and exclude an associated arteriovenous fistula, distal ischemia, infection or rupture.Pearl: Do not rely only on the yin-yang sign; demonstrate the to-and-fro waveform at the neck to confirm the diagnosis.
2. Record distal pulses, Doppler waveforms and, when relevant, ankle-brachial index before injection. Confirm patency of the parent artery and adjacent vein.Pearl: A documented baseline makes subtle post-injection arterial embolization easier to recognize.
3. Reconstitute thrombin using the manufacturer-specified diluent and concentration, commonly 1000 IU/mL. Transfer a small volume into a 1 mL Luer-lock syringe and clearly label it.
4. Position the patient to provide a stable acoustic window and expose the pseudoaneurysm. Perform sterile preparation, draping and local anesthesia while avoiding puncture of the sac during lidocaine infiltration.
5. Advance a 21–25 G needle under continuous real-time ultrasound into the residual flowing portion of the pseudoaneurysm. Place the needle tip near the periphery of the sac and as far from the neck as practical.Pearl: Use an in-plane trajectory and keep the needle tip visible at all times.
6. Before injection, confirm that the needle tip lies freely within the flowing sac and not in the parent artery, neck, adjacent vein or mural thrombus. Use real-time B-mode during injection because color Doppler may momentarily obscure the needle and developing echogenic clot.
7. Slowly inject approximately 100–200 IU at a time, equivalent to 0.1–0.2 mL when using 1000 IU/mL thrombin. Observe for echogenic clot forming around the needle tip and spreading through the sac over several seconds.Pearl: Dose to the Doppler endpoint rather than to sac volume; many pseudoaneurysms thrombose with 200–500 IU.
8. Pause after every aliquot and reassess the sac with color Doppler. If flow persists, confirm that the needle tip remains within the residual perfused compartment before administering another small aliquot.Pearl: Allow several seconds for thrombus propagation before deciding that additional thrombin is required.
9. Stop injecting immediately when color Doppler shows complete absence of flow within the pseudoaneurysm. Do not inject the remaining prepared thrombin once the endpoint has been achieved.
10. Reassess the parent artery, distal arteries and adjacent vein using color and spectral Doppler. Recheck distal pulses, limb temperature, capillary refill and neurologic status before leaving the procedure area.Pearl: New distal pain, paresthesia, pulse loss or waveform deterioration should be treated as arterial embolization until excluded.
11. Remove the needle, apply brief gentle pressure to the skin puncture and place a sterile dressing. Avoid aggressive compression that may distort the newly formed clot or compromise the parent vessel.
12. Perform immediate final duplex documentation and arrange repeat duplex ultrasound at approximately 12–24 hours. Repeat injection may be undertaken if clinically significant residual or recurrent flow persists and the anatomy remains suitable.

Complications

• Native-artery thrombosis or distal thromboembolism, approximately 0.8%
• Deep venous thrombosis, approximately 0.2%
• Residual flow or recurrent pseudoaneurysm, approximately 4–6%
• Hypersensitivity or anaphylaxis, rare
• Pseudoaneurysm rupture or expanding hematoma, rare
• Local infection or abscess, rare

Exam pearls

• Yin-yang flow is seen within the sac; the to-and-fro waveform at the neck is the diagnostic spectral Doppler sign.
• Position the needle away from the neck and inject the lowest effective dose in small aliquots.
• Stop injecting immediately when Doppler flow disappears; do not dose according to sac volume.
• UGTI remains effective in many anticoagulated patients, whereas anticoagulation reduces the success of compression therapy.
• Always document parent-artery, distal-artery and adjacent-vein patency before and after injection.
• A short wide neck and associated arteriovenous fistula increase thromboembolic risk.
• New distal pain or loss of pulse during injection is arterial embolization until proven otherwise.

Viva questions

What are the diagnostic Doppler findings of a pseudoaneurysm?

Color Doppler demonstrates bidirectional swirling yin-yang flow within the sac. Spectral Doppler at the neck shows a to-and-fro waveform, with systolic flow into the sac and diastolic flow back into the parent artery.

Where should the needle tip be positioned during thrombin injection?

The tip should lie within the residual flowing portion of the sac, preferably near its periphery and as far from the neck as possible. The needle tip, neck and parent artery must remain visible throughout injection.

What thrombin concentration and dose are commonly used?

A commonly used concentration is 1000 IU/mL. Thrombin is injected in small 100–200 IU aliquots with Doppler reassessment after each dose; many pseudoaneurysms thrombose with a total dose of approximately 200–500 IU, although the required dose varies.

What is the endpoint of thrombin injection?

The endpoint is complete disappearance of Doppler flow within the sac and neck, with preserved patency of the parent artery, distal arteries and adjacent vein and unchanged distal perfusion.

Why is a short, wide neck dangerous?

A short, wide neck permits thrombin to escape rapidly into the parent artery, causing native-artery thrombosis or distal embolization. Protected techniques or surgical or endovascular alternatives should be considered.

Can thrombin injection be performed during anticoagulation?

Yes. Unlike ultrasound-guided compression, UGTI usually remains effective during therapeutic anticoagulation. Anticoagulation should be interrupted only after assessing the indication, bleeding severity and thrombotic risk.

What is the most feared complication of UGTI?

The most feared complication is thrombin escape into the parent artery causing acute arterial thrombosis or distal embolization. Immediate recognition requires continuous ultrasound monitoring and comparison of distal pulses and arterial waveforms before and after injection.

How do you manage recurrent flow after initially successful injection?

Repeat duplex mapping and perform another low-dose injection if the sac and neck remain suitable. Repeated failure, a wide neck, associated arteriovenous fistula or a very large lesion should prompt balloon-assisted treatment, covered stent placement, embolization or surgery.

References