INTRODUCTION
Scalp arteriovenous fistulas (sAVFs), also referred to as cirsoid aneurysms or scalp arteriovenous malformations (AVMs), are infrequent vascular anomalies defined by direct communication between feeding arteries and draining veins without an intervening capillary bed. These lesions frequently involve branches of the external carotid artery (e.g., superficial temporal or occipital arteries) and drain into the superficial venous system. sAVFs are clinically relevant due to their potential for cosmetic disfigurement, hemorrhage, and neurological symptoms such as tinnitus or headache [1-4].
The pathogenesis of sAVFs includes congenital, traumatic, and iatrogenic etiologies. Congenital variants may be associated with syndromic presentations or occur as isolated anomalies. Acquired sAVFs often result from penetrating trauma, surgical interventions, or procedures such as hair transplantation [5-8].
Digital subtraction angiography (DSA) remains the gold standard for vascular mapping, while computed tomography angiography and magnetic resonance angiography are used adjunctively to assess intracranial-extracranial connections [7]. Historically, management included surgical resection or ligation, with high recurrence and morbidity. The advent of endovascular techniques, particularly the use of liquid embolic agents (LEAs), has revolutionized the treatment paradigm [6-9].
ihtObtura is a newer nonadhesive LEA composed of ethylene-vinyl alcohol (EVOH) copolymer dissolved in dimethyl sulfoxide (DMSO) and combined with an iodine-based radiopaque component. In the CLARIDAD trial [10], ihtObtura was evaluated for the embolization of brain AVMs, dural AVFs, and tumors, demonstrating feasible delivery, effective embolization, and progressive post-embolization radiopacity loss. However, its use in superficial extracranial vascular lesions, where cosmetic outcomes and follow-up imaging are particularly relevant, remains limited.
CASE REPORT
A patient in their 30s presented to the National Institute of Neurology and Neurosurgery in 2022 with an enlarging pulsatile scalp mass of left frontotemporal region, increasingly audible bruit, and progressive worsening headache. The patient denied any history of trauma, surgical interventions, or other risk factors associated with the development of sAVFs.
One year ago, the patient had undergone partial endovascular treatment with PHIL 25 (MicroVention) at another institution. Despite the intervention, the lesion persisted with progressive enlargement and symptoms exacerbation. Physical examination revealed a prominent pulsatile mass over the frontotemporal region, with audible bruit. DSA confirmed a high-flow AVF supplied by branches of the superficial temporal arteries, and both ophthalmic arteries with dilated venous drainage (Fig. 1).
Treatment and Procedure
The patient underwent percutaneous embolization under general anesthesia. A direct puncture technique was employed to access the venous dilation associated with the fistula. Under fluoroscopic guidance, a 21-gauge needle was inserted into the dilated venous structure. Previously, a compression belt was positioned around the head in order to reduce the venous outflow and control the migration of LEA into the lungs. Contrast injection confirmed the positioning of the needle withing the draining vein of sAVFs close to the fistulous connection (Fig. 1).
A total of 12 mL of ihtObtura 20 was slowly administered while the outflow vein was compressed to successfully close the draining vein, and retrogradely, fill the fistulous connections and the feeding arteries, achieving complete occlusion and total exclusion of the fistula from the circulation. The procedure was carefully monitored using real-time fluoroscopy to ensure effective embolization without dangerous reflux or non-target embolization. Post-procedure angiography confirmed the successful obliteration of the fistula. No intraoperative complications were observed (Fig. 1).
Outcome and Follow-Up
The patient experienced immediate clinical improvement after the procedure, with resolution of the audible bruit and pulsatility of the scalp mass. Follow-up imaging at 3, 6, and 12 months demonstrated persistent complete occlusion of the sAVF, without residual or recurrent fistula, and the patient remained asymptomatic at the 36-month clinical follow-up. Fluoroscopic assessment showed progressive loss of ihtObtura radiopacity, with complete radiopacity loss observed by 8 weeks. Clinically, the treated region showed progressive contour improvement, absence of skin tattooing or discoloration, and volume reduction of the embolized mass. No additional surgical intervention was required (Fig. 1).
On CT and magnetic resonance imaging (MRI) follow-up, the imaging appearance of ihtObtura was consistent with previously published observations for this embolic agent [10-14]. Specifically, CT demonstrated reduced beam-hardening artifact over time, while MRI showed no relevant susceptibility-related artifact.
DISCUSSION
ihtObtura is a 3rd-generation LEA based on EVOH copolymer dissolved in DMSO and combined with a non-metallic iodine-based contrast agent. Unlike tantalum-based EVOH agents such as Onyx and Squid, and iodine-bound copolymers such as PHIL, ihtObtura has distinctive follow-up imaging properties, including progressive post-embolization radiopacity loss, reduced beam-hardening artifacts on CT, and absence of relevant susceptibility-related artifacts on MRI [10-14].
Table 1 summarizes selected compositional, handling, and follow-up imaging characteristics of ihtObtura and other commonly used LEAs. This comparison is based on published descriptions of these agents and available clinical experience and should be interpreted cautiously because direct head-to-head comparative clinical data remain limited.
The disappearance of radiopacity is primarily due to the intrinsic radiolucency of EVOH and the progressive diffusion of the iodine-based component out of the vascular malformation post-embolization [13].
This property allows for improved assessment of embolized regions during follow-up imaging, reducing artifact-related obscuration seen with other agents such as Onyx, and is of special interest in case of a recurrence when retreatment is needed, or in high volume lesions that require management in a staged treatment strategy [10].
In clinical trial experience, operators have reported highly favorable penetration and diffusion of ihtObtura compared with their prior experience using other available LEAs, with low observed rates of vascular rupture and microcatheter occlusion. However, these observations should be interpreted cautiously because direct head-to-head comparative clinical data remain limited [10-14].
Current LEA such as Onyx and Squid, which are EVOHbased agents containing tantalum powder for radiopacity, produce persistent subcutaneous tattoo effects in superficial AVMs which is an important cosmetic drawback [9]. Although PHIL, a copolymer agent with iodine-based contrast, was developed to avoid tantalum LEA limitations, the precipitation kinetics has limited its expansion. ihtObtura represents a new LEA with a lack of tantalum with precipitation kinetics similar to Onyx-Squid.
Another postembolization drawback of Onyx, Squid, and PHIL is the presence of a permanent mass after embolization, which is a recognized reason for surgical resection to improve cosmetic results, even if complete occlusion of the lesion has been achieved. In our first experience with ihtObtura in a superficial vascular malformation, we observed a significant and progressive reduction in the residual mass, present after embolization, during the following weeks.
The mechanism underlying the progressive reduction of the treated superficial mass remains uncertain and is likely multifactorial. In this case, the finding may reflect elimination of high-flow arteriovenous shunting, thrombosis and remodeling of the arterialized venous pouch, and reduction of the embolized compartment after definitive occlusion. Although previous studies have described progressive radiopacity loss after ihtObtura embolization, attributed to elimination of the iodine-based radiopaque component over time, as well as favorable follow-up imaging characteristics [10-14], a direct relationship between the material properties of ihtObtura and volume reduction in superficial lesions has not yet been established. In our case, the reduction of the mass after embolization was clinically relevant, and the planned surgical excision was ultimately cancelled. This observation is promising because it suggests a potential role for ihtObtura in selected superficial vascular lesions in which avoidance of surgery, local complications, and postsurgical scarring is desirable. However, this finding should be considered preliminary and requires confirmation in larger series with standardized volumetric and cosmetic follow-up.
This case illustrates the successful treatment of a sAVF using ihtObtura, with complete angiographic occlusion, durable clinical improvement, absence of skin tattooing, and progressive reduction of the embolized superficial mass. These findings suggest that ihtObtura may be a useful option for selected superficial vascular lesions in which durable occlusion, follow-up imaging, and cosmetic outcome are clinically relevant.
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