Spinal Dural Fistula
Pearls
Delayed venous drainage from the artery of Adamkiewicz is present in the majority of patients presenting with spinal dural arteriovenous fistulas (DAVFs).
In the 10 to 15% of cases where the spinal DAVF is supplied by a radiculomedullary artery that also supplies the anterior or posterior spinal arteries, open surgical obliteration is indicated.
There has been no study demonstrating a difference in clinical symptoms in patients successfully treated by surgery or endovascular methods.
In the past several years, intraoperative indocyanine green (ICG) near-infrared videoangiography has emerged as a rapid and safe alternative to spinal digital subtraction angiography (DSA) for confirmation of the obliteration of a fistula.
There have been reports of late clinical deterioration following long periods of improvement or stabilization.
Spinal dural arteriovenous fistulas (DAVFs) are the most common heterogenous group of spinal vascular malformations, with varied natural histories, pathophysiologies, and treatment strategies.1 – 3 Although these lesions represent a rare cause of myeloradiculopathy, they remain potentially curable if diagnosed in a timely fashion.4 , 5 Due to the insidious nature of symptom onset, these patients rarely seek care from a neurosurgeon directly, but rather present to their primary care physician or neurologist. For that reason, knowledge of this disease must extend past the neurosurgical community. With advances in modern imaging through magnetic resonance imaging (MRI) and computed tomography (CT) angiography, there are now improved noninvasive means available for earlier diagnosis.6 Along with advances in imaging, therapeutic options have been refined and include both endovascular and microsurgical options.4 , 7 , 8 Both can be effective in obliterating the arteriovenous shunt.
♦ History (Table 26.1)
The earliest descriptions of spinal vascular malformations were made by Virchow in 1865, who described them as neoplasms of the spine.9 Gaupp characterized these lesions in 1888 as “hemorrhoids” of the pia mater.2 These early descriptions led Fedor Krause to attempt the first exposure of one of these lesions in 1910. After the laminectomy, no attempt was made at treatment, and the patient had a poor outcome. Charles Elsberg in 1912 reported the first excision in a 13-year-old boy. Although this patient did not improve, a later attempt in 1916 in a densely paraplegic patient led to complete recovery in 3 months.2 This surgery concentrated on removing a 2-cm section of abnormally dilated vein. This successful attempt, the first recorded in the literature, was performed on purely clinical grounds without any preoperative imaging. A later trend toward more aggressive surgery with extensive stripping of the dilated, arterialized veins failed to match the results of Elsberg’s success and actually worsened the condition by exacerbating the underlying venous hypertension.
Sir Percy Sargent first correctly described the insidious neurologic decline through observations of his own patients and a review of the previous medical literature.2 Diagnosis of this disorder relied on these clinical symptoms until the first preoperative diagnostic study for a spinal dural arteriovenous malformation was completed by Perthes in 1927 using Pantopaque myelography.2 , 9 In 1926, Foix and Alajouanine described a rapidly progressing necrotic myelopathy that led to paraplegia and death. This syndrome, which bears their names, is believed to be due to an end-stage spinal DAVF.9
With a means of identifying these lesions, attempts were made to classify them based on anatomic structure. Cushing and Bailey in 1928 initially categorized these malformations as neoplasms and arteriovenous malformations.9 WyburnMason further refined this classification system in 1943 by differentiating the lesions into arteriovenous malformations (AVMs) and purely venous malformations.2
The development of spinal angiography and the field of interventional neuroradiology in the 1960s redefined spinal DAVFS and allowed for a detailed understanding of the angioarchitecture of these lesions. Centers in London, Paris, and the National Institutes of Health (NIH) in the United States collaborated in these advances, making way for improved preoperative planning and advanced treatment options.9 Kendall and Logue10 first localized the spinal DAVF to the dural sleeve in 1977. They described a simple means to treat this lesion with surgical interruption of the fistulous point.
Since that time, the most often utilized classification system categorizes vascular malformations in four basic groups. Spinal DAVFs are classified as a type I lesion and are the primary topic of this chapter.
♦ Classification
Purpose of Schemes
The drive to classify spinal vascular malformations began in earnest with the descriptions by Wyburn-Mason based on posthumous histopathology and has since been redefined by selective angiography.9 Various classification schemes have been used since that time with varying nomenclature.1 , 2 , 11 The most often used classification scheme differentiates spinal vascular malformations based on the location of the pathology, the arterial supply, and the venous drainage. This classification is valuable, not only for its simplicity, but also for its insight into the pathophysiology, natural history, and treatment options. Although this classification system works for most lesions, some spinal vascular malformations may incorporate multiple characteristics from various classes. We will mention the other classes of spinal AVMs briefly, as it is important to understand what distinguishes type I spinal DAVFs from other spinal vascular malformations.
Type I: Spinal Dural Arteriovenous Fistulas
Previously called angioma racemosum venosum by WyburnMason, the type I spinal AVMs are DAVFs between a radicular artery and a medullary vein at the nerve root sleeve2 , 9 , 12 ( Fig. 26.1A ). These lesions are further classified into type Ia, where there is a single arterial feeder, and type Ib, where there are multiple fistulous points. The majority of spinal DAVFs are single arterial feeder types (Ia) and are low-flow lesions.12 It has been reported that 3 to 12% of all spinal cord lesions are vascular in pathology. Of this group, approximately 70 to 80% are spinal DAVFs.2 , 5 They occur most commonly in the lower thoracic and upper lumbar spine at the level of the conus medullaris. Type I spinal arteriovenous fistula (AVFs) are found predominantly in men over 40 years of age, with the median age being 57 years.
The lesion may have multiple arterial feeders but drain to a single draining vein. The fistulous point lies transdurally at the nerve sleeve, with the draining vein located intradurally.3 Venous drainage from the fistula is directed rostrally in most cases. As a result of the fistula, the direction of flow reverses in the valveless medullary vein, and blood travels from the intradural medullary vein into the coronal venous plexus, which becomes engorged and dilated.13 These dilated veins are present solely on the dorsal surface of the spinal cord in 85% of cases.2 It is important to note that spinal DAVFs typically do not share blood supply with the neural parenchyma of the spinal cord.
Although most commonly located in the thoracic and upper lumbar spine, these lesions may be found throughout the spinal cord. In the cervical spine, the radicular feeding arteries may arise from the thyrocervical, costocervical, vertebral, or external carotid arteries. In the lower lumbar and sacral spine, arterial feeders can include branches from the iliac arteries. Spinal dural AVMs are believed to be acquired lesions, a belief supported by the age at presentation. Spinal DAVFs in young patients are very rare. There are also reports in the literature of patients undergoing diagnostic studies for disk disease with negative results, and later presenting with progressive myelopathy and a spinal DAVF.
Type II: Intramedullary Arteriovenous Malformations
Intramedullary AVMs are composed of a distinct, intramedullary nidus of vessels that is fed by the anterior or posterior spinal arteries ( Fig. 26.1B ). As with intracranial AVMs, there are direct connections between arteries and veins without intervening capillary beds. These congenital lesions are often referred to as glomus AVMs. Differing from spinal AVFs, intramedullary AVMs are high-flow and high-pressure systems.
Unlike type I lesions, intramedullary AVMs occur with equal incidence in both men and women and may be located throughout the spinal cord. They typically present in children and young adults with acute symptoms of hemorrhage from the AVM but ultimately may present at any age. Treatment often includes a combination of presurgical embolization and subsequent surgical resection.
Type III: Diffuse Spinal Arteriovenous Malformations
Diffuse, metameric, or juvenile AVMs are extensive congenital vascular malformations that tend to involve both intramedullary and extramedullary tissues2 ( Fig. 26.1C ). These lesions may extend to the extraspinal tissues including the surrounding bone and skin. The least common of the spinal cord vascular malformations, they are also the most difficult to treat. These lesions normally present in adolescents and young adults and are characterized by their large size, high flow, and numerous feeding arteries. The nidus of the AVM is different from type II AVMs as it is large, loose, and interspersed within the spinal cord. There is functional spinal cord present inside the AVM, adding to the difficulty of treating these lesions. Cobb’s syndrome refers to an extremely rare type III AVM that involves multiple embryologic layers.2 Although the treatment for type III AVMs is similar to that for type II, outcomes are typically worse.
Type IV: Perimedullary Arteriovenous Fistulas
Type IV AVMs are intradural, extramedullary, direct arteriovenous fistulas from the anterior spinal, or, less commonly, the posterior spinal artery to the venous system on the pial surface of the cord.11 , 14 Unlike type II and III AVMs, these lesions are completely outside the spinal cord ( Fig. 26.1D ). The resultant fistula leads to venous hypertension within the spinal cord. Perimedullary fistulas most commonly occur in the thoracolumbar region at the conus medullaris of the spinal cord. There is no sex predilection in type IV lesions. These congenital or acquired lesions may be subclassified as types IV-A, IV-B, or IV-C based on the size and flow characteristics. Treatment options are based on subclassification and are summarized in Table 26.2 .
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