INTRODUCTION
Dural arteriovenous fistulas (dAVFs) account for 10-15% of intracranial arteriovenous malformations and are defined by anomalous shunts between dural arteries and dural venous sinuses or cortical veins [2]. Clinical presentation is highly dependent on venous drainage pattern. Lesions with direct cortical venous reflux are classified as “aggressive,” carrying annual hemorrhage risks of 7-20% [8].
Venous aneurysms associated with dAVFs are generally believed to arise from long-standing venous hypertension, ectasia, and turbulent flow [5]. Most reported cases of venous aneurysm rupture in DAVFs are accompanied by angiographic evidence of venous congestion [12]. Localized focal hemodynamic stress caused by venous angulation or stenosis may also induce aneurysm formation and rupture in otherwise normal-calibre veins [10]. In contrast to diffuse venous hypertension, which results in widespread venous congestion and ectasia, focal venous hypertension acts locally on a single venous segment, producing a discrete saccular aneurysm rather than generalized dilation.
In this report, we present a rare case of ruptured venous aneurysm associated with a dAVF that showed no diffuse angiographic signs of venous hypertension. This case underscores the importance of recognizing localized venous pressure gradients as a potential mechanism for aneurysm formation and rupture.
CASE DESCRIPTION
A 51-year-old right-handed woman with no significant past medical history presented to the emergency department with a sudden-onset speech disturbance and right-sided weakness. According to family members, she developed acute dysphasia followed by collapse at home, without a preceding headache and seizures. There was no previous history of head injury, neurosurgical procedure, or intracranial infection.
On admission, she was alert but exhibited expressive aphasia with preserved comprehension. Neurological examination revealed dense right hemiparesis (Medical Research Council [MRC] grade 2/5 in the upper limb and 3/5 in the lower limb), brisk deep tendon reflexes, and an extensor plantar response on the right. Cranial nerve examination was unremarkable, and there were no signs of raised intracranial pressure. Blood pressure was within normal range, and no cranial bruit was detected.
Non-contrast computed tomography (CT) demonstrated a large left parietotemporal intracerebral hematoma with subarachnoid extension (Fig. 1). Digital subtraction angiography (DSA) confirmed a left temporal dural arteriovenous fistula (dAVF) supplied by the middle meningeal artery and draining via the veins of Trolard and Labbé into the superior sagittal sinus (Fig. 2).
Importantly, DSA demonstrated a discrete saccular venous aneurysm arising at a sharply angulated segment of the draining vein (Fig. 3). The remainder of the vein was of normal caliber, without diffuse ectasia or reflux, indicating the absence of diffuse angiographic venous hypertension. The aneurysm was therefore considered the most likely source of hemorrhage, attributed to focal hemodynamic stress at the site of angulation.
The patient underwent transarterial embolization via selective catheterization of the left middle meningeal artery using a microcatheter. Onyx-18 liquid embolic agent was injected under fluoroscopic guidance until complete obliteration of the fistulous connection and exclusion of the venous aneurysm were achieved (Fig. 4). The procedure was uneventful, and she was discharged on postoperative day 3. At one-month follow-up, her neurological recovery was excellent, with complete resolution of aphasia and marked improvement in motor function.
DISCUSSION
Venous aneurysms are rare vascular lesions and, when associated with dural arteriovenous fistulas (dAVFs), are traditionally regarded as sequelae of chronic venous hypertension within the draining system. The present case is remarkable because the venous aneurysm formed and ruptured in the absence of diffuse angiographic evidence of venous hypertension—such as venous congestion, reflux, or delayed emptying, thereby challenging the conventional paradigm of DAVF-related vascular pathology. Instead, a discrete saccular aneurysm was seen at a sharply angulated and stenotic venous segment, suggesting focal venous hypertension, which is restricted to a segment of a draining vein subjected to turbulent flow or outflow stenosis.
Venous ectasia represents a fusiform or diffuse dilation of the draining vein, whereas a venous aneurysm is a focal, saccular outpouching that typically arises at sites of venous tortuosity, branching, or angulation. Histopathologic studies have shown that aneurysmal segments exhibit loss of elastic lamina and smooth muscle, reflecting localized structural weakening of the venous wall. In large clinical cohorts, including the 511-patient analysis by Wan et al., venous complications such as ectasia, thrombosis, and hemorrhage were strongly correlated with cortical venous reflux and hypertension [12]. Likewise, most aneurysms described in the context of DAVFs are flow-related, developing either in arterial feeders or at venous outlets subjected to sustained hemodynamic stress [1,9].
However, recent reports indicate that venous aneurysm formation can occur without diffuse venous hypertension. Kim et al. presented two patients with ruptured venous aneurysms in dAVFs, both located adjacent to significantly curved or stenotic venous segments, suggesting that localized hemodynamic stress can act as an independent pathogenic factor [10]. Hashiguchi et al. similarly described an anterior cranial fossa DAVF complicated by a ruptured venous aneurysm at a venous branching point, implicating increased focal stress rather than diffuse hypertension [7]. Im et al. reported a comparable case with long-term observation, reinforcing that venous aneurysms may arise from altered local flow dynamics even in the absence of venous ectasia [8].
Histopathological studies also provide insight. Hamada et al. showed that venous aneurysms presenting with intracerebral hemorrhage exhibit more severe degenerative wall changes—such as thinning, loss of elastic lamina, and smooth muscle depletion—compared with those developing under venous hypertension [6]. These findings suggest that structural fragility of the venous wall may act synergistically with focal hemodynamic stress to predispose to rupture. Thus, our case likely represents the spectrum of localized focal venous hypertension that does not produce diffuse angiographic congestion but remains pathophysiologically significant.
In the absence of trauma or prior neurosurgical intervention, this dAVF may have developed spontaneously, possibly due to age-related venous sinus wall fragility or an unrecognized episode of dural sinus thrombosis leading to pathological arteriovenous shunting.
The clinical implications are substantial. Intracranial hemorrhage occurs in up to 42% of dAVFs with cortical venous drainage, with even higher rates when venous ectasia or aneurysm formation is present [2,3]. Cognard et al. reported that hemorrhage was observed in 40% of DAVFs with direct cortical venous drainage, and up to 65% when venous ectasia coexisted [4]. However, as illustrated by our case and similar reports, rupture may still occur despite the absence of diffuse angiographic hypertension. Therefore, any venous aneurysm identified in a dAVF should be considered clinically significant and treated proactively.
Management strategies must be individualized. Endovascular embolization remains first-line, enabling simultaneous treatment of both the fistulous connection and associated aneurysm, as in our case. Microsurgical disconnection continues to be valuable in selected situations when embolization is not feasible [9,10]. While spontaneous resolution of venous aneurysms has been reported following treatment of the underlying fistula [11], the unpredictable rupture risk—particularly in non-hypertensive aneurysms—argues for a proactive therapeutic approach whenever possible.
CONCLUSIONS
This case highlights that venous aneurysm rupture in a dural arteriovenous fistula (dAVF) may occur even in the absence of diffuse angiographic venous hypertension. The sharply angulated and stenotic draining vein in our patient likely produced localized focal venous hypertension, creating turbulent flow and structural weakening that culminated in aneurysm formation and rupture. Recognizing this distinction between diffuse and focal venous pressure changes broadens the understanding of dAVF pathophysiology and underscores that aneurysms should never be considered benign, even when global venous congestion is absent. Early angiographic identification and prompt endovascular treatment remain essential to prevent rebleeding and improve clinical outcomes.
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