Spinal extradural arteriovenous fistula (SEDAVF) is defined as an abnormal direct connection between paraspinal or paravertebral arterial system and neighboring veins, particularly those of the extradural venous plexus, without any intervening vessels such as normal capillaries or dysplastic nidus.^1)6)11) It is known as an exceedingly rare disease that arises secondarily after iatrogenic or mechanical trauma and occurs spontaneously in connective tissue disease.¹²⁾

SEDAVF can cause compressive radiculopathy or myelopathy due to mechanical compression of root sleeve or thecal sac by dilated extradural venous plexus,^14)22)27) and congestive myelopathy due to increased medullary venous pressure by intradural retrograde blood reflux.¹³⁾¹⁷⁾ In addition, in the case of high-flow arteriovenous shunting in which arterial feeder occurs directly in vertebral artery (VA), there can be not only sensations of bruit or tinnitus,^7)19)20)28) but also cerebellar symptoms such as vertigo and ataxia caused by vascular steal effect.¹⁶⁾

Because of the complicated anatomical structures, uncommon nature and diverse clinical manifestati ons of SEDAVF, early diagnosis and proper treatment of the disease are not easy. The treatment goal in SEDAVF is to obliterate the vascular shunting point, blocking all anomalous pathways. In the present study, we report a rare case of cervical SEDAVF presenting compressive radiculopathy of right upper extremity and treated using transarterial balloon-assisted coil embolization.

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A 77-year-old woman complained of radiating pain in right posterior neck and shoulder that had lasted a month, as well as intermittent tingling sensation from posterior neck to fingertips that had persisted for 2 weeks. The woman had no mechanical trauma history but had undergone internal jugular catheterization for mitral valve replacement operation 4 years ago. A local spine clinic made a provisional diagnosis of cervical spondylosis, and multiple osteophytes of cervical spine were observed in cervical spine computed tomography (CT) without contrast medium. The patient underwent a nerve block to relieve pain, and the pain was somewhat relieved. According to the doctor’s advice, she took oral medication for pain relief and had enough rest for 2 weeks.

However, the patient visited the emergency medical center at our hospital immediately upon discovering subjective weakness of right shoulder abduction and elbow flexion. Upon physical examination, the patient showed a manual muscle testing (MMT) grade of 4 for both right shoulder abduction and elbow flexion, accompanied by hypoesthesia of light touch in the right C6 dermatome. The deep tendon reflex (DTR) of her right biceps and brachioradial muscle were reduced, but those of her right triceps muscle were normal, and no upper motor neuron sign was observed.

Cervical spine magnetic resonance imaging (MRI) without contrast medium showed no signs of high signal intensity or swelling in the spinal cord, but axial T2-weighted images revealed multiple abnormal flow voids in the right intervertebral foramina at C1–2, C2–3, C3–4, C4–5, and C5–6. Subsequently, because we suspected that these lesions are due to the spinal vascular malformation, we performed MRI with contrast medium, which clearly showed irregular enhanced lesion at the same levels. However, there were no signs of spinal cord compression, intradural flow voids, or enhanced perimedullary vessels penetrating inside the thecal sac (Fig. 1). In maximum intensity projection reconstruction of neck carotid magnetic resonance angiography (MRA), an engorged paraspinal venous system was observed in most cervical spine. Using volume-rendered images of computed tomographic angiography (CTA), we found anomalous fistulous communication between the extraosseous VA and its adjacent vertebral vein, just before entry into the C6 transverse foramen (Fig. 2).

The patient was hospitalized to allow digital subtraction angiography (DSA), which provided a definitive diagnosis of spinal arteriovenous shunting. Meanwhile, her MMT grades for right shoulder abduction and elbow flexion had worsened to 2 and 3, respectively. The thyrocervical and costocervical trunks of the right subclavian artery were not involved in the pathological lesion, nor were any branches of the external carotid artery. Selective injection into the right VA revealed a high-flow fistula occurring directly at the C6–7 level and draining into the neighboring extradural venous plexus. Consequently, abnormal observations of the vertebral vein, intervertebral vein, and anterior internal vertebral venous plexus were made in the arterial phase (Fig. 3).

Based on cervical spine MRI, neck carotid CTA, and DSA, the patient was diagnosed with a high-flow cervical SEDAVF of the vertebro-vertebral subtype with a single orifice and without intradural perimedullary venous reflux, which appears to be caused iatrogenically by internal jugular catheterization. The patient’s symptoms were manifestations of compressive radiculopathy caused by a dilated paraspinal venous system. We decided to obliterate this pathological lesion using endovascular treatment. To eliminate the fistula, we scheduled transarterial balloon-assisted coil embolization and administered 100 mg of aspirin and 75 mg of clopidogrel daily for 1 week before the operation.

Under local anesthesia and systemic heparinization, a 5-Fr diagnostic catheter (Simmons^®; Terumo, Tokyo, Japan) was inserted into the left femoral artery to confirm the flow of the left VA responsible for the blood supply of the posterior circulation. A 6-Fr guiding catheter (Envoy^®; Codman, MA, USA) was then inserted into the right femoral artery and guided to the right VA for fistula obliteration. Distal 1.7-Fr and proximal 2.4-Fr microcatheters (Headway 17^®; Microvention, CA, USA), along with 0.014 inch microwire (Transend^®; Stryker, MI, USA), were navigated to the right VA as close to the shunt point as possible through the right-side guiding catheter, and then entered into the oval venous pouch of the right vertebral vein. To prevent coil herniation, balloon inflation was performed in front of the fistula orifice during embolization using a 4×15 mm (diameter×length) occlusion balloon (Scepter C^®; Microvention, CA, USA). Five varied sizes of detachable coils (10×34 mm [Presidio^®; Codman, FL, USA], 6×10 mm, 5×20 mm, 4×10 mm [Axium^®; Medtronic, MN, USA], and 3×6 mm [Orbit Galaxy^®; Codman, FL, USA]) were deployed into the venous pouch of the SEDAVF and repositioned carefully until a stable position was obtained. Blood flow to the fistula was significantly reduced by packing the coils and the arteriovenous connection of the right VA and vertebral vein was finally occluded (Fig. 4).

No new neurological complications occurred, and the radiating pain in the woman’s right posterior neck and shoulder dramatically improved, as did the tingling sensation in her right arm. Brain MRI showed no ischemic or hemorrhagic lesions. The patient was discharged with a prescription of 100 mg of aspirin daily. Since the procedure, the patient has continued to participate in clinical follow-ups through outpatient department. After 5 months, the patient’s MMT grade for right shoulder abduction and elbow flexion improved significantly to 4, and her motor weakness and pain completely disappeared after 8 months, although she remained slight hypoesthesia in right wrist. Neck carotid CTA performed after 12 and 24 months showed no signs of fistula recurrence (Fig. 5).

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Unlike spinal dural arteriovenous fistula (AVF), whose shunt point can be predicted relatively well and which has a higher prevalence among spinal vascular malformations, the concept and classification of SEDAVF remains unclear as seen in mixed terminologies, such as paraspinal AVF, paravertebral AVF, vertebro-vertebral AVF, vertebro-jugular AVF, and intercoastal AVF. SEDAVF is difficult to diagnose early because this clinical entity is too rare to be reported only in case reports or small case series, and it presents a wide range of clinical manifestations depending on the location of the fistula and on whether intradural drainage is present.²³⁾²⁴⁾ Unfortunately, in our case, it was regarded as a common cervical spondylosis in the elderly, so the low possibility of spinal vascular malformation was not predicted until motor weakness occurred. In addition, some reported cases involving venous hypertension in the spinal cord have led to irreversible results within a short period, with patients suffering permanent disability.^{5)9)13)17)18)} Thus, early detection and evaluation are the first key to achieving favorable outcome.

SEDAVF shows different neuropathological characteristics depending on whether there is intradural involvement.²³⁾²⁴⁾ SEDAVF with pure extradural drainage causes compressive radiculopathy or myelopathy due to mass effect by engorgement of extradural venous plexus.^14)22)27) The patient’s right C5 and C6 radiculopathy was attributable to the dilation of the right intervertebral veins and anterior internal vertebral venous plexus. SEDAVF with intradural perimedullary venous drainage causes congestive myelopathy by prolonged chronic high pressure, and if left unrecognized, it can also trigger spinal cord infarction or hemorrhage,^5)9)17) and even subarachnoid hemorrhage at high cervical location.¹³⁾¹⁸⁾ High-flow SEDAVF with direct shunting of VA uniquely causes cerebellar symptoms by vertebrobasilar insufficiency as well as pulsatile bruit or tinnitus,^{7)16)19)20)28)} but our patient did not show such a distinctive symptom. Therefore, although SEDAVF is rare, this pathology should be considered in the differential diagnosis of spinal radiculopathy or myelopathy and other mentioned symptoms.

Endovascular treatment is currently the favored initial method of treatment in cases of SEDAVF due to its lesser invasiveness.^1)11)23) Trying direct surgical manipulation on multiple arterial feeders, large venous pouch, high flow fistula, or involvement at multiple spinal levels is a risk of massive bleeding. Various endovascular techniques and instruments used in cerebral vascular disease, are similarly used to successfully eliminate lesions. However, unlike the brain, there are some differences and limitations. Onyx is a liquid embolic agent that can safely permeates small, tortuous, and distal vessels, but liquid agents are inappropriate because they can trigger unintentional migration in high-flow SEDAVF with large-volume venous pouches, such as that seen in the present case. For this reason, it is limitedly used as a supplementary purpose for embolizing the remaining fistulas after coil packing.²¹⁾ A transvenous route through the dural sinus can be useful in the brain, but in the spine, it can be very restrictively considered only when the location of the fistula is accessible from vertebral vein or internal jugular vein.¹⁹⁾ Therefore, it is vital that clinicians plan appropriate treatments for which approach routes to access and which embolic materials to apply through a comprehensive understanding of the vascular structure of the arterial feeders, fistulas, and draining veins.

Complete obstruction of the parent artery where the fistula is located is probably the most effective method to block the shunt, but a few studies have reported vertebrobasilar ischemia or infarction when the VA is sacrificed.³⁾⁴⁾ This is likely to be more likely with dominant VA, but the risk for this has not been clearly identified, so some studies have attempted to block the lesions while preserving the parent artery (Table 1). In some limited cases with a single arterial feeder or a small fistula orifice, selective coil packing was possible only in the fistula.^2)3)10)25) When embolization was not feasible with transarterial coiling alone, the balloon and covered stent were used as alternatives. The balloon assistance, as in our case, can be used to reduce the high-flow of fistula and prevent coil herniation or migration.¹⁹⁾ The sole use of detachable balloon was also reported,⁸⁾ but it has not been approved in our country. The covered stent can be used when the fistula has a large orifice or there is a risk of exacerbation of compressive symptoms resulting from coil embolization.^7)15)28) However, it might be somewhat inappropriate in the tortuous upper segment of VA because of the stiffness of covered stent and the risk of occlusion of small branch vessels. No best treatment guideline has yet been established so far, and further research such as systemic review and meta-analysis is required.

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It should be recognized that the SEDAVF can be a causative disease in patients with spinal radiculopathy or myelopathy. It is also important to precisely diagnose using comprehensive radiologic imaging modalities. That is, prompt detection and evaluation, accurate diagnosis, and proper treatment can lead to a good clinical outcome despite the complexity and peculiarity of SEDAVF. Through the endovascular treatment with transarterial balloon-assisted coil embolization, we were able to obtain complete closure of SEDAVF with preservation of the parent artery by occluding only the venous pouch.

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