Ruptured venous aneurysm associated with a dural arteriovenous fistula: Two case reports

Abstract

BACKGROUND

In general, venous aneurysm associated with dural arteriovenous fistula (dAVF) is considered to be developed under long standing venous hypertension and manifested as venous ectasia of draining vein itself. However, discrete saccular shaped venous aneurysm without angiographic evidence of venous hypertension arising from the draining vein, like cerebral arterial aneurysm, is quite rare and its pathomechanism remains unclear in patients with dAVF.

CASE SUMMARY

In this report, we present two cases of ruptured saccular venous aneurysms associated with dAVF without venous hypertension or venous ectasia. In both cases, significant curve or stenosis is observed in draining vein, which is located in just distal portion of the venous aneurysms. These aneurysms were successfully treated with a transarterial embolization. Underlying mechanism of venous aneurysms in these cases is discussed.

CONCLUSION

Although there is little doubt that hemodynamic stress has a critical role in the development of venous aneurysms in patients with dAVF, preceding venous hypertension or venous ectasia is not necessary for development and enlargement of venous aneurysms. Considering the significant risk of rupture, a careful review of draining vein features including tortuosity or stenosis is needed, especially in venous aneurysms without evidence of venous hypertension.

Key Words: Dural arteriovenous fistula; Venous aneurysm; Hemodynamic stress; Intracranial hemorrhage; Embolization; Case report

Core Tip: Venous aneurysms associated with dural arteriovenous fistula (dAVF) have been generally considered to be developed in the setting of venous hypertension or venous ectasia. However, saccular venous aneurysm in patients with dAVF could develop without preceding venous ectasia or venous hypertension and this situation is very rare. So, its pathomechanism remains unclear in patients with dAVF. In this report, we present rare cases of venous aneurysms in the absence of venous hypertension, and describe underlying unique angiographic features; presence of curved or stenotic portion within long and tortuous draining vein.

INTRODUCTION

There has been an established consensus that treating intracranial dural arteriovenous fistula (dAVF) with cortical venous drainage (CVD) reduces the risk of intracranial hemorrhage (ICH), that is associated with increased mortality as high as 10.4%[1].

However, clinicians often face dilemma when dAVFs are detected incidentally or presented with benign symptoms without CVD. Moreover, when angiogram reveals several unique radiologic features such as deep vein drainage, long tortuous drainage vein, or venous aneurysm in asymptomatic patients with dAVF, it is difficult to establish treatment plan.

Venous aneurysms seem to be developed from ectatic drainage vein under long standing venous hypertension and are significantly related to an increased risk of ICH[2,3]. However, discrete saccular venous aneurysm arising from the draining vein, like cerebral arterial aneurysm, without angiographic evidence of venous hypertension or venous ectasia is quite rare and little is known about its natural course and pathomechanism.

In this report, we present rare cases of ruptured venous aneurysm associated with dAVF without venous hypertension, successfully treated with transarterial embolization, and we discuss the underlying angiographic features.

CASE PRESENTATION

Chief complaints

Case 1: A 65- year-old female was emergently transferred to our hospital due to a sudden onset of headache and dizziness.

Case 2: A 58- year-old male was admitted to our hospital due to a persistent headache that had lasted for several months.

History of present illness

Case 1: A 65- year-old female was emergently transferred to our hospital due to a sudden onset of headache and dizziness.

Case 2: The 18 months ago, he had detected an ICH in the right occipital lobe accompanied by an aneurysmal lesion. However, he received conservative treatment without further examination at that time.

History of past illness

Case 1: She had a medical history of hypertension and diabetes mellitus.

Case 2: He had no previous medical history.

Personal and family history

There were no relevant personal and family history.

Physical examination

Case 1: Upon arrival, her Glasgow Coma Scale score was 14 (E3, V5, M6).

Case 2: There was no significant any neurological deficits in the physical examination.

Laboratory examinations

Platelet counts and coagulation profile were normal at the time of admission.

Imaging examinations

Case 1: A computed tomography (CT) scan revealed an intraventricular hemorrhage (IVH), particularly in the 4^th ventricle (Figure 1A and B). In addition, CT angiography (CTA) showed an aneurysmal lesion with hemorrhage in the 4^th ventricle (Figure 1C). Initially, we suspected that this hemorrhage was due to a ruptured PICA aneurysm. However, digital subtraction angiography (DSA) revealed dAVF at the posterior cranial fossa supplied by the petrosal branch of the right middle meningeal artery and drained into the left transverse sinus. The dilated pouch through the course of the draining vein suggested a venous aneurysm, which is consistent with CTA findings (Figure 1D and E). A significant stenotic segment of the draining vein is detected immediately distal to the aneurysm (Figure 1F).

Figure 1 Images of case 1. A and B: Axial computed tomography (CT) shows acute intraventricular hemorrhage in all ventricles; C: There is an aneurysmal lesion within the 4^th ventricle hemorrhage on CT angiography. Right antero-posterior and lateral external carotid artery angiogram showing the dural arteriovenous fistula with venous aneurysm (black arrowhead) fed by petrosal branch of the right middle meningeal artery and drained to left transverse sinus; D and E: There is no evidence of venous ectasia or obstruction in the left transverse sinus; F: Note that the draining vein immediately distal to the aneurysm shows a significant angled appearance (black arrows); G: Transarterial embolization with histoacryl (mixed with lipiodol) was performed and final angiogram shows complete obliteration of the fistula; H: Magnetic resonance angiography, obtained 1 year after embolization, shows no evidence of recurrence with disappearance of venous aneurysm.

Case 2: Previously, CT, magnetic resonance imaging (MRI), and magnetic resonance angiography (MRA) scans from another hospital 18 months ago had detected an ICH in the right occipital lobe accompanied by an aneurysmal lesion (Figure 2A and B). The MRI and MRA scans at admission revealed an enlarged previous aneurysmal lesion within encephalomalacic change resulting from a previous hemorrhage (Figure 2C and D). This lesion was supplied by the right occipital artery and drained into the dilated internal cerebral vein, suggesting dAVF. Subsequently, DSA was performed, revealing a dAVF supplied by the right occipital artery and drained into the superior sagittal sinus and internal cerebral vein. The dilated pouch through the course of draining the vein suggested venous aneurysm was noted, which is consistent with MRA findings (Figure 2E and F). An obvious curve and stenosis were observed at the immediately distal segment of the aneurysm within the draining vein (Figure 2G).

Figure 2 Images of case 2. A and B: Axial computed tomography and magnetic resonance angiography (MRA), 18 months before admission, shows intracerebral hemorrhage in the right occipital lobe, and there is an aneurysmal lesion within the hemorrhage; C and D: At admission, MRA shows slightly enlarged previous aneurysmal lesion, and this lesion was supplied by a right occipital artery with dilated internal cerebral vein suggesting dural arteriovenous fistula (dAVF) (white arrowheads); E and F: Right antero-posterior and lateral external carotid artery angiogram shows the dAVF with venous aneurysm fed by the right occipital artery and drained to internal cerebral vein and superior sagittal sinus. There is no definite evidence of venous ectasia or obstruction in the venous outlet; G: A rotational 3-dimensional imaging demonstrates a significant curve and stenosis immediately distal to the aneurysm (white arrows); H: Transarterial embolization with histoacryl (mixed with lipiodol) was performed, and the final angiogram showed complete obliteration of the fistula.

FINAL DIAGNOSIS

Ruptured venous aneurysm associated with dAVF.

TREATMENT

Case 1

Considering the risk of recurrent bleeding, transfemoral arterial embolization with histoacryl (mixed with lipiodol) was performed. Immediately after embolization, DSA showed a complete obliteration of the fistula (Figure 1G).

Case 2

Considering the history of ICH associated with this lesion, transfemoral arterial embolization was performed using histoacryl (mixed with lipiodol). Immediately after embolization, DSA showed a complete obliteration of the fistula (Figure 2H).

OUTCOME AND FOLLOW-UP

Case 1

A follow-up CTA and DSA obtained 2 weeks after embolization showed disappearance of the venous aneurysm. Throughout her admission, the patient gradually recovered to baseline neurologic condition without any complications. A follow-up MRA at 1 year after embolization showed no evidence of recurrence (Figure 1H).

Case 2

He was discharged without any complications.

DISCUSSION

Clinical symptoms of dAVF range from asymptomatic to severe symptoms such as ICH or non-hemorrhagic neurologic deficits, including seizures, parkinsonism, and cerebellar symptoms[4,5]. These symptoms almost always correlate with the pattern of venous drainage and the anatomic location of the fistula[6,7].

ICH has been reported in 35%-42% of dAVF cases, and it is generally accepted that the venous drainage pattern is the most important factor in predicting ICH[1,8]. Several studies have reported that the presence of CVD further increases the risk of hemorrhage, especially when coupled with cortical venous ectasia or aneurysm formation[9,10]. Cognard et al[11] reported that hemorrhage was present in 40% of direct CVD cases and in 65% of direct CVD cases with venous ectasia. In addition, sinus outflow thrombosis or obstruction may accelerate the formation and progression of venous ectasia, potentially leading to rupture.

However, although most venous ectasia or venous aneurysms tend to develop and progress in scenarios involving venous hypertension, such as venous outlet thrombosis, they have also been observed to develop or enlarge without any associated venous hypertension or changes in the venous outlet[2,12,13]. Hashiguchi et al[2] reported ruptured venous aneurysm associated with a dAVF of anterior cranial fossa. In this report, venous aneurysm had developed at the branching site of the two major venous drainers, which may cause increased hemodynamic stress without venous hypertension. Im et al[12] also concluded that venous aneurysm associated with a dAVF of anterior cranial fossa may result from increased hemodynamic stress in the absence of changes in the venous outlet.

In our cases, the venous aneurysms were located in the stenotic, a significantly curved section within long and tortuous draining veins, just distal to the aneurysm. There was no clear sign of venous ectasia or occlusion of the venous outlet. Thus, we could postulate that preceding venous hypertension is not necessarily required to develop a venous aneurysm. Similar to arterial aneurysms, venous aneurysms may develop in the areas with a significant curve or stenosis in the draining veins where hemodynamic stress occurs in patients with dAVF. Increased localized intravenous pressure in these areas may contribute to the development and enlargement of aneurysm.

In the histopathological study, the venous aneurysms presenting with ICH differed from those developed under venous hypertensive conditions in patients with dAVF[6]. Degenerative changes, including irregular wall thickness, loss of internal elastic lamina, and decreased smooth muscle cells, were more severe in venous aneurysms presenting with ICH than in those with venous hypertension. This result also supported that patients with venous aneurysms presenting with ICH do not necessarily manifest venous hypertension before the insult, and thus it remains unclear whether venous aneurysms presenting with ICH accompanied by venous hypertension progress to venous aneurysms.

Hemodynamic stress undoubtedly plays a major role in the formation of venous and enlargement of venous aneurysms may be part of the natural course of dAVF leading to ICH. However, more complex interactions between hemodynamic stress, degenerative factors, and anatomical factors may seem to be involved in the formation of venous aneurysms. These factors may include location of dAVF, degenerative factors leading to histological changes in drainage vein, and factors related to drainage vein, which is most important, such as existence of stenotic and curved portion, or branching site within the drainage vein, in the setting of long and tortuous drainage course. Further study is needed to fully understand venous aneurysms in patients with dAVF.

CONCLUSION

Although rare, venous aneurysms associated with dAVF could develop without preceding venous ectasia or venous hypertension. When dealing with these lesions, care should be taken not to overlook the radiologic features of draining veins as seen in our cases predicting enlargement and rupture of venous aneurysm.