Figura 1. Magnetic resonance angiography. .

Figura 2. Baseline angiography.

Figura 3. Embolization of the second pedicle. Percutaneous puncture of the third pedicle.

Figura 4. Final angiography.

Clinical case:

A 17-year-old male patient with no history of cardiovascular disease presented with right plantar angioma. He had a history of multiple unsuccessful embolizations (partial results). Due to persistent symptoms, including swelling and pain in the right heel that significantly impacted his quality of life, he sought consultation at our Department.

His assessment began with a contrast-enhanced magnetic resonance angiography (MRA) of the right foot. The study revealed a 50-mm lobulated formation within the posterior subcutaneous adipose tissue, located beneath the calcaneal margin and in contact with the plantar fascia. This lesion was compatible with an arteriovenous malformation (AVM), showing arterial supply and venous drainage. Arterial supply to the AVM originated from the peroneal and posterior tibial vascular bundles (Figure 1).

Following a multidisciplinary discussion, a decision was made for endovascular treatment involving embolization of the AVM using Onyx 18® and Onyx 34® as embolizing agents. The decision-making process considered the following aspects: 1) the stability of the material, (2) the anatomical location of the AVM and the need to preserve the plantar fat pad, since Onyx® does not cause tissue necrosis, and (3) the material’s controlled release, which would allow for complete penetration and occlusion of the vascular lesion without subsequent degradation.

The procedure was performed under epidural anesthesia using a percutaneous antegrade puncture of the right femoral artery. Operators placed a 6-Fr introducer sheath. A lower limb arteriography confirmed that the posterior tibial artery was the sole feeder of the AVM (Figure 2).

Selective injections into the posterior tibial artery revealed three feeding pedicles.

A Rebar 27® microcatheter (Medtronic Minneapolis, USA) was advanced into the proximal pedicle, and embolization was successfully performed using one vial of Onyx 18® and one vial of Onyx 34®. A Rebar 18® microcatheter was then placed in the second pedicle, and embolization was completed with one vial of Onyx 18®. While the procedure was successful, it was insufficient to fully occlude the AVM (Figure 3). A third Rebar 18® microcatheter (Medtronic Minneapolis, USA) was advanced toward the third pedicle; however, a safe position for embolization could not be achieved. After heparin reversal, ultrasound-guided puncture of the AVM was performed using a 20-G Abbottcath® needle. Once correct positioning was confirmed angiographically, another vial of Onyx 18® was administered. This achieved success and the procedure was finalized (Figure 4).

The patient showed favorable post-procedural progress with adequate pain control and is currently under joint follow-up with the orthopedic team. To date, there has been no symptomatic recurrence of the malformation.

This case was presented due to the highly unpredictable prognosis of peripheral AVMs, the less common type of malformation. These vascular anomalies result from disrupted vascular system development at different stages of embryogenesis. They are defined by abnormal connections between arteries and veins, characterized by the absence of a capillary network. These abnormal connections form the “nidus” of the malformation.

AVMs are usually asymptomatic for years and may become evident after trauma or during puberty, due to hormone changes.

The treatment is aimed at occluding or eliminating the AVM nidus while avoiding proximal ligation or embolization. This objective can be achieved through endovascular, surgical, or mixed treatment approaches. In symptomatic, simple AVMs, the first-line treatment is endovascular embolization with a strategy tailored to the specific AVM type. If possible, excision surgery of the nidus should be combined with this approach to achieve a potentially definitive treatment. A combination of endovascular techniques—including transarterial, transvenous, and direct puncture approaches—is frequently used in the management of these malformations.

Currently, there are several agents available for endovascular embolization, with liquid (ethanol) and semi-liquid (Onyx®, histoacryl) agents being the most commonly considered. In this case, Onyx® was chosen as the embolizing agent due to its biocompatibility, non-degradable nature, and non-adhesive properties. This agent is available in two formulations:

Onyx 18® (6% EVOH), which is less viscous and more suitable for distal embolizations, and

Onyx 34® (8% EVOH).

Recommendations to prevent complications during and after Onyx® use:

Shake Onyx® for at least 20 minutes in a specialized machine right before administration.

Use a specialized microcatheter that is DMSO resistant, to prevent its dissolution.

After flushing the microcatheter with saline, the lumen should be filled with DMSO to prevent copolymer precipitation.

Once injected, Onyx® advances like molten lava into the embolization site. The injection should be slow, never exceeding 0.3 mL/min, and can be spaced up to 2 minutes, so that prior injections can set and redirect the embolizing agent. Final solidification occurs within 5 minutes from administration.

Onyx® reflux should not be allowed beyond 1 cm from the catheter tip.

After completing the procedure, operators should wait a few seconds, apply slight aspiration, and gently stretch the catheter to detach it from the solidified Onyx®.

This material is contraindicated in cases or renal and/or hepatic dysfunction, prior reaction to DMSO, vasospasm impairing blood flow, and unstable catheter positioning preventing safe embolization.

We can conclude that arteriovenous vascular malformations are rare pathological entities requiring a multidisciplinary approach. The primary treatment goal is the complete elimination of the nidus, thus preventing recurrence. Given the availability of multiple embolizing agents, endovascular therapy should be strongly considered, as it can often lead to definitive resolution and consequently improve patient quality of life.

1. Senkichi J. Embolic agents. Intervencionismo. 2016;16(1):16-26

2. Escalante J. Vargas Román A. Embolization of Arteriovenous Malformations with Onyx. Neuroeje 25 (2) Julio-Diciembre 2012

3. Fernandez-Alonso L.Tratamiento quirúrgico de las malformaciones vasculares. Anales Sis San Navarra [online]. 2004, vol.27, suppl.1 [citado 2022-09-15], pp.127-132.

4. Lojo Rocamonde IM. Endovascular treatment of congenital vascular malformations: Materials and techniques. Lojo Rocamonde, I. M. (2014). Tratamiento endovascular de malformaciones vasculares congénitas. Materiales y técnicas. Angiología, 66(5), 274–276.

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