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ORIGINAL CONTRIBUTIONS

Received: October 22^nd 2014

Accepted: March 6^th 2015

Endovascular treatment of spinal dorsal intradural arteriovenous fistulas

Jorge Arturo Santos-Franco,^a María Griselda Lizbeth Collado-Arce,^a Julio César Dávila-Romero,^a Rafael Saavedra-Andrade,^a Miguel Antonio Sandoval-Balanzario^a

^aServicio de Neurocirugía, Hospital de Especialidades Centro Médico Nacional La Raza, Instituto Mexicano del Seguro Social, Distrito Federal, México

Communication with: Jorge Arturo Santos-Franco

Telephone: (55) 2096 9023

Email: jasantosfranco@hotmail.com; jorge_santos@unam.mx

Background: The dorsal spinal intradural arteriovenous fistulas (DSIAF) are infrequent and complex injuries are underdiagnosed condition and disability. The aim is to present our experience in the endovascular management.

Methods: A retrospective and prospective study of patients with DSIAF treated by endovascular therapy (EVT) with n-butyl-cyanoacrylate during the period 2007-2013.

Results: 15 patients, 12 men and 3 women, mean age 37 years, were included. In 12 cases, the presentation was progressive and insidious over a period between 6 months and one year, while 3 had bleeding. The lesion in the thoracic location had 73 % of cases, lumbar 20 % and cervical 7 %. Prior to treatment observed disability grades 5 and 4 in 73 %, and 67 % had micturition disturbances. Complications grade 3, only one patient had transient deterioration of alert 6 hours after the procedure. Improvement to grades 1 and 2 disability at 48 hours, 3 and 6 months, 53 %, 73 % and 87 % respectively was found.

Conclusions: EVT has a short operating time, bleeding volume is very low and the hospital stay is short compared with other surgical techniques. EVT is a safe and significant effectiveness in treating DSIAF procedure. This is the first series of cases treated with EVT in Mexico.

Keywords: Arteriovenous fistula; Arteriovenous malformations; Spinal cord vascular diseases

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Spinal vascular malformations are complex and uncommon injuries representing a heterogeneous group of injuries that directly or indirectly affect the spinal cord. The group includes arteriovenous malformations and dural arteriovenous fistulas which in turn are divided into epidural and intradural.^1-5

Dorsal spinal intradural arteriovenous fistulas (DSIAF) lead to patient disability, either through: hypoxia (vascular steal phenomenon), through congestion and compression (for ectasia and venous hypertension) or hemorrhage (rare). Because of its natural history, which is ominous for spinal function, DSIAF should be treated. Endovascular treatment has evolved substantially.⁵

Methods

From November 2007 to October 2010, records and imaging studies were reviewed retrospectively for patients with DSIAF who were treated by neurological endovascular therapy (NET) in the service of the Neurocirugía del Hospital de Especialidades at the Centro Médico Nacional La Raza. From November 2010 to November 2013 patients were prospectively enrolled with the same characteristics, and data such as sex, age and occupation were recorded.

To establish a clinical evaluation, all patients were classified in on the scale of degree of motor impairment, gait and urination according to Aminnof and Logue (Tables I-III).⁶ Time was recorded from the beginning of the clinical evaluation until the time of diagnosis.

Patients were treated with NET under sedation and analgesia. Via the femoral artery the radicular artery involved in the fistula was catheterized. The arterial flap was selectively catheterized by 1.5 F microcatheter mounted on a 0.008 "or 0.007" microwire. Superselective embolization was performed with a mixture of lipiodol with n-butyl cyanoacrylate, from the pedicle to the foot of the vein. Eventualities or complications from treatment (Figure 1) were recorded. Patients were assessed 48 hours after the procedure, and length of hospital stay was recorded. Patients followed a physiotherapy program in hospitals with rehabilitation services (Hospital de Rehabilitación Colonia, Hospital “Dr. Victorio de la Fuente Narváez” y Hospital de Traumatología y Ortopedia Lomas Verdes).

Patients were evaluated 3 and 6 months later by Aminoff and Logue motor disability scale, and Barthel disability index.

Results

During the study period 20 patients with DSIAF were examined, 12 in the retrospective part and 8 in the prospective phase. Of these, two patients were excluded for refusing an invasive treatment and only 18 patients were treated. Fifteen patients were managed by EVT, and three were treated by thoracic laminectomy. Of 15 patients, 12 were male (80%) and 3 female (20%), the average age was 37 years (R: 17-62).

The course of the DSIAF was insidious and progressive in 12 cases (80%) with an average of 6 months to 1 year prior to definitive diagnosis. Three patients (20%) suddenly presented with spinal hemorrhage, causing quadriplegia in one and paraplegia in two. One of these patients developed intracranial subarachnoid hemorrhage complicated with acute hydrocephalus, which confused and delayed the etiologic diagnosis (Figure 2).

The most frequent symptoms were motor and sensory disturbances. There was decreased strength in 100% of patients to varying degrees, from mild paresis to paraplegia in 3 patients and quadriplegia in one. In 5 patients (33%) claudication appeared.

By analyzing patients with the Aminoff and Logue motor condition scale we observed that 7 patients (47%) were in grade 1, and 3 patients (20%) in grade 2, which shows the severity of the motor damage (Table I).

Among the sensory disturbances, diffuse or poorly defined hypoesthesia was found. Hypoesthesia below the level of involvement of the vascular lesion was present in 14 patients (93%), and 1 patient (7%) had no sensitivity condition. Radicular pain occurred in 8 cases (53%).

Sexual disorder characterized by erectile dysfunction occurred in 67% of males (8/12), and all cases manifested micturition disorders with incontinence or urinary retention. On the Aminoff and Logue scale of micturition disorders we observed that 67% were in grade 3.

In assessing the degree of functional impairment according to the Aminoff and Logue modified scale of disability for walking, it was observed that at diagnosis, 60% and 13% of patients were in grades 5 and 4, respectively (Table II).

All patients underwent magnetic resonance imaging (MRI). In the 3 cases of acute onset, hemorrhage was seen. The most important findings were medullary thickening in 8 cases (53%), and T2 hyperintensity sequence in 9 (60%). These changes indirectly indicate medullary suffering. Vascular tortuosity image was observed in all cases. A patient with thoracic vascular injury also presented cervical syringomyelia (Figure 2).

Selective spinal angiography was performed on all patients. The shunt was thoracic in 11 patients (73%), lumbar in 3 (20%) and cervical in only one case (7%). In 10 cases (67%) the shunt consisted of a single afferent (type A) and 5 cases (33%) two afferents (type B). In assessing the venous drainage, it was observed that in 11 cases (73%) it was caudal, in 3 cases (20%) it was in cephalic and caudal, and in one case (7%) it was only cephalic.
Patients were treated with EVT with the selective injection of n-butyl-cyanoacrylate. The procedures were uncomplicated and without immediate contingencies, except in one patient who presented severe sensory and motor deterioration 6 hours after the procedure (case 8) because of probable perimedullary vein thrombosis secondary to inadvertent migration of embolization material into the venous drainage. Fourteen patients (93%) were discharged within 48 hours of the procedure, while the patient who presented the complication was hospitalized for a week. We assessed patients according to Aminnof and Logue level of disability for walking and urination, upon discharge, at 3 months and at 6 months. Functional evolution toward improvement was evident, reaching grades 1 and 2 in 40%, 60% and 70% at 48 hours, 3 months and 6 months respectively. The details of the evolution are shown in Figures 3 and 4. Patients who remained in grade 5 up to 6 months were those who presented hemorrhagic lesion with cervical localization and the patient with the aforementioned complications.

According to the Barthel index, which measures the degree of dependence of patients, we found that at 6 months 73% of patients are independent, while one (6%) had a slight dependence and 20% severe dependence.

The average time of endovascular procedure was 40 minutes, the average bleeding volume was 30 ml, and average hospital stay was three days, due to in-hospital administrative issues.

Discussion

Intradural spinal arteriovenous fistulas are classified into dorsal and ventral, and are entities with different anatomical location and clinical behavior.^4,7

DSIAF occurs when an afferent radicular artery abnormally communicates with the venous system of the spinal cord in the dural sleeve of the nerve root causing venous hypertension.^8-12 They are classified as type A and B, if there are one or more than one afferent radicular artery, respectively.¹³ They represent about 70% of spinal vascular lesions and their incidence is higher in men.⁵ They are often located in the thoracic spine and their etiology is unknown, but they are associated with spinal conditions such as infection, trauma and surgery. The clinical course is usually progressive and insidious and occasionally they bleed.^5,12,14,15

In our study 20% began with hemorrhage. Motor symptoms occur in almost all cases. Flaccid paresis is almost as common as spastic. Sensory symptoms are present in 69 to 90% of cases and more than half experience pain. MRI is usually the method of initial diagnosis and the most common findings are T2 spinal hyperintensity and enhancement with gadolinium administration in T1.⁵ The coronal venous plexus has a nodular characteristic, and a shaggy and tortuous appearance with multiple signal voids conditioned by afferent and drainage vessels. There may be changes in signal intensity on T2 representing marrow edema due to venous congestion. Subacute bleeding is observed as an increase in signal T1 images. The association of vascular malformation and syringomyelia is rare,¹⁶ but it has been seen in one patient (Figure 2).

Angiography is the gold standard⁵ and shows a characteristic pattern of low flow produced by the radiculomedular afferent artery penetrating the dura mater at the level of dural cover of the root, and at that level the fistula is formed that arterializes the coronal venous plexus.^17-19

The functional prognosis of DSIAF is bad, and most patients may develop abnormal motion within a year from the start of symptoms and only 9% can roam unrestricted three years out, and 50% are effectively invalids.^20,21

Before deciding on treatment, one must be certain of the type of injury, based on a spinal angiography and proper analysis of the images of RM.^14,22-24 There is no uniformity in the classifications, and that makes the analysis of DSIAF more complicated. The classification proposed by Spetzler et al. is the most appropriate.^4,5,15,24 DSIAF can be treated by surgery or EVT. Some authors prefer to treat them in the first instance by surgery, which was traditionally accepted.^4,14 Spitteler et al. reported very low morbidity with 80% improvement, however, in 10% clinical condition worsened and 10% remained unchanged.⁴

Surgery is a good strategy, without being fully effective, entailing the need for general anesthesia, laminectomy or laminoplasty of at least two or three levels, prolonged procedure time, postoperative pain and risk of infection, in addition to hospitalization generally in excess of 72 hours.

Embolization was considered useful as an adjunct or alternative to surgery,²⁵ however, today many authors recommended it as first-line treatment of choice.^1,5,26,27

Even so, one must affirm that endovascular treatment is not good because recanalization rate is high. This is based on a study of 3 patients recruited in a period of 4 years²⁸ treated by embolization, which all showed short vascular recanalization. Claiming that embolization is inadequate for DSIAF according to that article is wrong because: 1) it includes only three patients with arteriovenous fistula, without defining whether they are ventral or dorsal, and 2) the polyvinyl alcohol particles used for embolization have a high rate of recanalization and the risk of passing very far into the venous side of the shunt.^5,27,29,30

In conclusion, it is a study with no force because of its inadequate definition of DSIAF, with few patients and endovascular technique outside the current context. Furthermore, the article refers to 13 studies available then, 157 spinal vascular lesions, not defined with recanalization at 8%, with varied embolization materials such as collagen gel, polyvinyl alcohol, microballoons, muscle, fragments of dura mater, iso-butyl-cyanoacrylate and n-butyl-cyanoacrylate.^31-42

Meta-analyses and reviews of the effectiveness of endovascular management in spinal fistulas report it as a safe and effective technique, and point out that the current trend is to regard it as the first line of treatment.^5,26 With the emergence of new microcatheter technology and liquid embolic materials, especially n-butyl-cyanoacrylate, permanent healing has been reported between 70 and 100%.^{5,23,25,26,43-47} Another cause of recanalization is poor endovascular technique. Embolic material penetration should include the proximal portion of the draining vein (vein foot).^1,5,27 Ethylene-vinyl alcohol (EVOH) is a liquid embolic material widely used in the world because its injection is more controllable than n-butyl-cyanoacrylate, as well as its safety and effectiveness in managing various intracranial vascular pathologies, especially in arteriovenous malformations (AVM) and fistulas.^48,49 EVOH seems to be ideal in the treatment of the DSIAF, and has been reported to be effective in other types of spinal vascular lesions,⁵⁰ but more studies are required to document its clinical utility. The presence of very small arterial pedicles preventing superselective catheterization, severe atherosclerosis of the pedicles or anastomosis with the anterior spinal artery and / or the Adamkiewicz artery that cannot be avoided, are the major technical limits for endovascular management. These cases should be treated first by surgical management.⁵

Few articles report both surgical and endovascular complications, however you can see spinal ischemia by occlusion of normal arteries, especially the anterior spinal artery or the Adamkiewicz artery.^26,51 In our study, one patient presented deterioration of spinal function due to venous thrombosis resulting from very distal passage of liquid embolic material into the coronal venous plexus, a complication that has not been reported previously and would probably have been avoided by using a more controllable embolizing agent as EVOH.

Conclusions

Vascular spinal malformations are uncommon injuries, still not well understood, and they lack a unified classification criterion. DSIAF should be diagnosed as early as possible because of their poor functional prognosis. Endovascular management and surgery are a good strategy for treatment, however, embolization has advantages over surgery, such as being minimally invasive, use of sedation, shorter procedure time, the absence of extensive laminectomy or laminoplasty than could cause long term instability of the spine and the rare possibility of infection, and the possibility of early rehabilitation. For these reasons endovascular therapy could be considered as the first choice, leaving surgery as an alternative treatment for these injuries. To our knowledge, this is the largest Latin American study described and the first in Mexico that reports on the endovascular management of this type of injury.
Furthermore, in this series we present a case of syringomyelia and intracranial subarachnoid hemorrhage associated with spinal arteriovenous fistula, which are rare situations.

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