Pure arterial malformation (PAM) is a rare cerebrovascular anomaly characterized by a coil-like cluster of dilated, tortuous, and overlapping arteries without associated venous components or arteriovenous shunting [1,2]. Since first being described as a distinct entity in 2013 by McLaughlin et al. [2], PAM has remained poorly understood, and its natural history is still under debate. Initially considered a benign vascular anomaly, PAM is often discovered incidentally on imaging studies performed for unrelated conditions [3,4]. However, growing evidence suggests that PAMs may exhibit progression or even rupture, particularly when associated with aneurysmal changes [5-7].

While most cases have been managed conservatively, recent reports have shown that symptomatic or progressive PAMs may benefit from interventional approaches, including microsurgical resection [8], bypass surgery [9], endovascular embolization [6,10], or radiosurgery. Nevertheless, the role of stereotactic radiosurgery in the treatment of PAMs has not been well established, and to date, no standardized treatment protocol exists.

We present a case of a PAM located at the origin of the left anterior choroidal artery, which was treated with Gamma Knife radiosurgery (GKRS). Follow-up imaging at 6 months showed significant lesion regression, and complete obliteration was confirmed 3 years post-treatment with no neurological complications. To our knowledge, this is one of the few reported cases of angiographically confirmed PAM obliteration following stereotactic radiosurgery. This case highlights the potential role of GKRS in the management of selected PAMs and contributes to the evolving understanding of this rare vascular entity.

A 58-year-old man was referred to our institution following the incidental detection of a vascular abnormality on brain magnetic resonance imaging (MRI) performed during routine health screening. A retrospective review of a brain MRI acquired approximately 2 years earlier showed no definite vascular abnormality at the corresponding location (Fig. 1A). On the current MRI, a fusiform dilatation in the lateral branch of the left posterior cerebral artery was observed (Fig. 1B).

Digital subtraction angiography (DSA) demonstrated a tightly clustered, tortuous arterial lesion originating from the left anterior choroidal artery without early venous drainage, consistent with a PAM. Of particular note was the presence of pseudoaneurysmal dilatation, characterized by focal dilation lacking a clearly definable vessel wall. Based on these features and previously described criteria by McLaughlin et al. [2], we diagnosed this lesion as a PAM associated with pseudoaneurysm (Fig. 1C, D).

Stereotactic radiosurgery was performed using Gamma Knife, delivering a marginal dose of 18 Gy at the 50% isodose line. The radiosurgical target was delineated based on high-resolution MRI (Fig. 2A), and the treatment plan was constructed to conform precisely to the lesion (Fig. 2B).

Follow-up MRI obtained 6 months after treatment showed a marked reduction in the size of the vascular lesion, with loss of its characteristic tortuous appearance (Fig. 2C). At the 3-year follow-up, DSA confirmed complete obliteration of the malformation and normalization of arterial morphology (Fig. 2D, E). The patient remained neurologically intact with no treatment-related complications throughout the follow-up period.

PAMs are rare intracranial vascular lesions defined by a cluster of tortuous, dilated arterial loops without any associated venous component or early venous drainage [2]. First delineated as a distinct entity in 2013, PAMs have since been reported across a range of anatomical sites, predominantly in young females and often involving the anterior circulation [1,4,9]. The anatomical features of PAM are illustrated in Fig. 3, adapted from McLaughlin et al. [2] with permission. Histologically and angiographically, PAMs must be carefully distinguished from other vascular anomalies such as dolichoectasia, arteriovenous malformations (AVMs), or fusiform aneurysms [11]. Unlike AVMs, PAMs do not display arteriovenous shunting, and unlike dolichoectasia—which typically involves the vertebrobasilar system and shows elongated but continuous vessels—PAMs present as a tightly coiled arterial mass often mimicking a nidus [3,11]. The pathological nature of PAMs remains incompletely understood. Since its first definition by McLaughlin et al. [2], PAM has been primarily recognized through imaging characteristics, including a tightly coiled cluster of dilated arteries without arteriovenous shunting or venous components. However, these features overlap with other vascular anomalies such as AVMs, dolichoectasia, and pseudoaneurysms. AVMs typically exhibit early venous drainage and a nidus, dolichoectasia demonstrates elongated, tortuous vessels with continuous flow patterns, and pseudoaneurysms present with localized outpouchings lacking intact arterial walls. In contrast, our case showed no venous component, no shunting, and a lesion configuration consistent with PAM. While histological confirmation was not feasible, our diagnosis was grounded in characteristic angiographic features supported by multiple previous reports.

While many PAMs are asymptomatic and incidentally discovered on magnetic resonance angiography or DSA [4,12], accumulating evidence suggests that their clinical behavior may not be universally benign. Several reports have described radiographic progression [3,6,13], symptomatic presentations such as compressive neuropathies [14], and even hemorrhagic events, particularly when PAMs are associated with aneurysmal dilatations [5,7,10]. In a systematic review of 37 PAM cases, Wójtowicz et al. [7] reported a hemorrhage rate of 44.4% in PAMs with aneurysms versus 15.8% in those without, highlighting the importance of vigilant monitoring and individualized treatment planning. PAM lesions associated with pseudoaneurysmal changes have been reported to carry increased risks of hemorrhage or progression. Thus, the decision for therapeutic intervention in our asymptomatic patient was based on careful consideration of potential risks, particularly due to lesion location and pseudoaneurysmal dilatation. GKRS effectively led to complete obliteration of both PAM and pseudoaneurysmal components without complications.

Treatment strategies for PAMs are not standardized and must be tailored to lesion location, accessibility, symptomatology, and presence of aneurysmal transformation. Microsurgical clipping or resection may be feasible in accessible locations, particularly when associated aneurysms are the suspected source of hemorrhage [8,15]. Endovascular options such as Onyx embolization and NBCA have been employed in select cases [10,16], while flow diverter stents have shown promise in hemodynamically complex lesions [17]. However, each modality carries procedural risks, especially when dealing with lesions involving eloquent or deep-seated arteries such as the anterior choroidal or perforating branches of the posterior circulation [10,18]. Although the patient was asymptomatic at the time of diagnosis, the decision to proceed with GKRS was based on the lesion’s deep location within the anterior choroidal territory and the presence of pseudoaneurysmal dilatation, which are both factors associated with an elevated risk of hemorrhage or progression. Prior reports have demonstrated that even asymptomatic PAMs may evolve or rupture, especially when aneurysmal features are present [18]. Given the surgically challenging location and potential complications of conservative observation, stereotactic radiosurgery was considered a justified and low-risk treatment approach in this context.

In our case, the lesion originated from the anterior choroidal artery, an anatomically critical and surgically challenging region. Stereotactic radiosurgery using the Gamma Knife system was selected to deliver a focused dose of 18 Gy to the nidus. The dose of 18 Gy was selected based on a balance between efficacy and safety. Given the lesion's location within the anterior choroidal territory—an eloquent and high-risk zone—we aimed to deliver a dose sufficient for vascular obliteration, referencing established protocols for deep-seated AVMs. Low-dose radiosurgery for AVMs has already been widely practiced, demonstrating effective outcomes in select cases. Additionally, reports of successful low-dose radiosurgery for cavernous malformations further supported our dosing rationale. Therefore, we selected a marginal dose slightly lower than typically used for AVMs, but slightly higher than the common dose for cavernous malformations, aligning with the lesion’s intermediate risk profile. Follow-up imaging revealed progressive lesion reduction at 6 months and complete obliteration at 3 years without neurological deficits or radiological evidence of radiation-induced injury. This case demonstrates the potential utility of GKRS in selected cases of PAM, particularly when traditional approaches pose significant technical or safety limitations.

The exact mechanism of radiosurgical effect on PAMs is not well established. However, by analogy to AVM treatment, focused irradiation may induce endothelial cell damage, vessel wall thickening, and eventual thrombosis, resulting in gradual lesion obliteration [3]. Radiosurgery may also offer a favorable safety profile by minimizing damage to surrounding brain structures, a critical advantage in treating deep or eloquent PAMs.

To our knowledge, this case is one of the first to document angiographically confirmed obliteration of a PAM following GKRS. It expands the therapeutic landscape of PAMs and suggests that, in appropriately selected patients, radiosurgery may serve as a viable, low-morbidity alternative to more invasive interventions. Nevertheless, further longitudinal data are needed to clarify optimal treatment criteria, define long-term efficacy, and understand radiographic predictors of favorable radiosurgical response.

PAMs are rare cerebrovascular anomalies with an incompletely understood natural history. While many are managed conservatively, selected cases with high-risk anatomical features or uncertain progression may benefit from intervention. In this report, we describe a case of a PAM originating from the anterior choroidal artery that was successfully treated with GKRS, resulting in complete angiographic obliteration without complications. This case highlights the potential role of stereotactic radiosurgery as a safe and effective alternative in anatomically challenging PAMs. Further studies are warranted to clarify treatment indications and long-term outcomes of radiosurgical management in this unique vascular entity.

Given the nature of a single case report, our findings should not be interpreted as establishing a standard treatment guideline for PAM. Rather, this case aims to contribute to the growing body of anecdotal evidence and stimulate further research into the radiosurgical management of PAMs, particularly those with pseudoaneurysmal components and surgically inaccessible locations.