Scalp arteriovenous fistulas (AVFs) are rare vascular anomalies characterized by abnormal connections between the arterial and venous systems within the scalp. These lesions can be congenital or acquired, with trauma and surgical interventions being the most common etiologies in adults [1-9]. Although scalp AVFs are uncommon, their clinical significance is substantial due to the potential for serious complications, including chronic headaches, tinnitus, cosmetic deformities, and, in severe cases, high-output cardiac failure or intracranial hemorrhage [3,10].

Current treatment strategies for scalp AVFs include endovascular embolization, surgical ligation, or a combination of both [11-17]. The choice of treatment is guided by the characteristics of the scalp AVF [18]. In this report, we present a case of scalp AVF that underwent transvenous embolization with balloon occlusion and Onyx (Medtronic).

A middle-aged female patient was admitted to the hospital, presenting with a pulsating mass on the left parietal scalp area for 20 years. She had no history of trauma or surgical procedure. Physical examination revealed a soft, tender, and pulsatile subcutaneous mass in the parietal region, measuring 3×4 cm, and there was no skin color change on the lesion. On brain magnetic resonance imaging, an AVF was detected in the left parietal scalp with multiple feeding arteries from the external carotid artery (ECA) and main venous drainage into the left external jugular vein (EJV). Cerebral angiography confirmed a scalp AVF with multiple arterial feeders of the occipital artery, middle meningeal artery, superficial temporal artery, supraorbital artery, and vertebral artery on the left side, draining mainly into the left superficial temporal vein (STV) and the left EJV (Fig. 1A–F).

The treatment strategy was discussed by the neurovascular team, and endovascular embolization was decided upon before surgery. Under general anesthesia, a transvenous and transarterial approach was performed at the same time; a 5 Fr Envoy guiding catheter (Cerenovus) was introduced into the left occipital artery, and a 6 Fr Envoy guiding catheter was introduced into the distal STV via the left EJV. Initially, the transarterial approach was attempted and failed because the tortuosity of the feeding arteries prevented access with a microcatheter to the distal fistulous point. Therefore, transvenous embolization with a balloon was attempted due to the single venous route, which can control outflow and deliver the embolic agent to the arterial bed during balloon occlusion. After occlusion of the left STV with a Sceptor C balloon catheter (4×10 mm, MicroVention), embolization was performed with 7.5 mL of Onyx-18 (Medtronics) through the same balloon catheter (Fig. 1G–I). Control angiography showed complete obliteration of the scalp AVF, and the patient was discharged without complications 2 days after embolization. At follow-up, no symptoms were noted, including mass effect, inflammation, and discoloration.

Scalp AVF is a rare vascular pathology with a heterogeneous angioarchitecture. Sofela et al. [3] reported that scalp AVFs were spontaneous in 60%, traumatic in 32%, and iatrogenic in 8% of cases. AVF and pseudoaneurysm were the most common manifestations, while AVF was even rarer. Scalp AVF was common in young females with a median duration of 3 years, and the most common symptoms were a pulsatile mass, headache, and tinnitus.

Surgical excision represents the initial treatment option for this vascular lesion, which can be complicated by the potential for significant bleeding and the possibility of scalp injury. As a result, endovascular therapy has been widely used as an alternative or adjunct to open surgery. A variety of endovascular techniques, including transarterial, transvenous, and direct puncture, have been developed to occlude the arteriovenous shunt, and various embolic materials such as coils, glues, and Onyx have also been used [2,11,12,14-17]. In a systemic review of 243 cases of scalp AVF [3], more than 50% of cases were treated with surgical excision alone, 21.6% with endovascular embolization alone, and 14.5% with hybrid methods. Complications were significantly higher in the EVT group, which showed transient scalp pain and the presence of residual mass after embolization, whereas scalp necrosis and wound infection were most common in surgical treatment [3,19]. However, there is a low recurrence rate after treatment regardless of the modality [3].

This complex vascular lesion was classified into 3 types by Yokouchi et al. [18]: type A, a single fistula fed by a single proximal feeding artery; type B, a single fistula fed by multiple arterial feeders; and type C, multiple fistulas with plexiform feeding arteries and a main dilated draining vein. Our case was type B, with multiple feeders from the ECA and draining mainly into the STV. In scalp AVF, the transarterial approach can be challenging due to the severe tortuosity of the feeders from the ECA. While distal access to the fistulous point may be achievable, pulmonary embolism from liquid embolic agents should be considered, given the characteristics of this scalp lesion with high-flow AVF. In this case, the balloon catheter was accessible via the STV as the primary venous route, and the liquid embolic agent could be safely injected during occlusion of the venous outflow, allowing retrograde filling of the feeding arteries. It was fortunate to achieve a successful embolization of the scalp AVF in a single session, and the symptom was resolved immediately with no procedural complications.

In this case, transvenous Onyx embolization was performed with the Sceptor C balloon, which has a dual-channel design that allows both balloon occlusion and Onyx injection within the balloon catheter. As a result, this embolization procedure was very simple and took less than 1 hour. In a previous report, transvenous embolization was performed using a single-channel Hyperform balloon (Medtronic), and Onyx embolization required an additional microcatheter for Onyx injection [17]. In addition, Onyx was chosen as the initial option because of its ability to occlude the shunt from the venous outlet to the arterial feeders, a process that may be facilitated by the non-adhesive properties of Onyx.

In conclusion, this case demonstrates that transvenous embolization with balloon occlusion is an effective treatment for complex scalp AVFs, especially when transarterial approaches are challenging. The successful outcome without complications highlights the importance of tailoring treatment strategies to the specific vascular anatomy of each patient.