MANAGEMENT OF SPINAL DURAL ARTERIOVENOUS FISTULA, A REVIEW WITH ONE CASE REPORT

Spinal dural arteriovenous fistulas (SDAVFs) are rare acquired vascular malformations of the spinal cord which if not treated properly, can lead to inevitable severe morbidity with progressive spinal cord symptoms. The management is still at high interest among specialists. If microsurgical treatment is still considered as a treatment of choice for SDAVFs, endovascular treatment is increasingly growing in interest with the development of endovascular techniques and new embolization materials. In this article, a short discussion is made about the spinal dural arteriovenous fistulae in respect to anatomy, etiology, diagnosis and treatment. Careful patient selection, a multidisciplinary approach and standardized surgical techniques can lead to excellent results with virtually no complications. Introduction ascular malformation of the spinal cord represents rare clinical condition characterized by a difficult diagnosis and complex management. Spinal dural arteriovenous fistulas (SDAVF) are the most common condition in these pathological entities with important clinical implications. These direct communications between radicular artery and medullary vein usually results in myelopathy due to venous hypertension. Assessment of a SDAVF is often difficult because of non-specific findings on non-invasive imaging modalities. With the advances in neuroimaging, micro neurosurgery and neuro endovascular techniques, the complete treatment of these pathological situations is very feasible with the possibility of complete remission of clinical symptomatology. Endovascular embolization was reported as an effective therapy in the treatment of SDAVFs that can be used as singular and definitive intervention in some particular cases. We present a particular case with SDAVF treated by endovascular embolization and discuss the treatment possibilities to more fully understand the optimal management of these lesions. Vascular Anatomy: Spinal cord vascularization is provided by the anterior spinal artery (ASA) and the paired posterior spinal arteries (PSA). The ASA consists of the junction of two branches originating from the two vertebral arteries proximal to the vertebra basilar junction. On its path, it receives contributions from branches of vertebral and ascending cervical arteries in the cervical region as well as from intercostal and lumbar arteries at the corresponding levels. The spinal meningeal arteries are branches of the segmental arteries founded at almost every spinal level supplying the dura in the spinal canal. Unlike these, spinal medullary arteries, which exist only at some levels, are implicated in spinal cord vascular perfusion. The artery of Adamkiewicz (great anterior spinal V Bas J Surg, June, 24, 2018 63 Management of spinal dural arteriovenous fistula M El Husseini, H Mouawia, A Mrad & T Chaaban Bas J Surg, June, 24, 2018 64 medullary artery) is the dominant thoracolumbar segmental artery with variable origin from T8 to L1 vertebral segments that connects to ASA and supplies the spinal cord (figures 1, 2a&b). The posterior spinal arteries arise from either the posterior inferior cerebellar or vertebral arteries (V3 or V4 segments) and as they descend on either side of the dorsolateral cord surface, they are reinforced by segmental/radicular branches. It make anastomoses with its fellow and with the anterior spinal artery. Fig.1, 2 a&b: Vascular anatomy of spinal cord Sited from: J.Vasc.Bras.2015,14(3):248-252 Etiology, Epidemiology and Pathophysiology: The etiology of vascular malformations of the spinal cord has not been clearly defined. Intradural parenchymal malformations arises in younger patient population and are believed to be congenital. However, spinal arterial dural fistulas commonly arises in elderly population and are believed to be due to trauma. These AVF malformations develops near a spinal dural artery, forming an abnormal arteriovenous communication with the venous circulation. SDAVF represents 70% of spinal arteriovenous shunts that commonly occur in the thoracic and lumbar spines of middle aged men. However, the disease seems to be underdiagnosed. The majority of SDAVFs occurs spontaneously, but a post-traumatic etiology cannot be excluded in a significant proportion of them. Typically, this disease affects male patients (in 80% of cases). The pathophysiology in spinal cord venous hypertension is due to one or a few small low-flow arteriovenous shunts between a spinal meningeal artery and a spinal medullary vein, typically located in the intervertebral foramen within the dura. The retrograde venous drainage circuit in SDAVF is represented by a spinal medullary vein into the peri medullary venous system and finally the medullary veins. The venous drainage of Management of spinal dural arteriovenous fistula M El Husseini, H Mouawia, A Mrad & T Chaaban the SDAVF is slow and expansive, and may reach the cervical spinal canal or cauda equina by ascending or descending blood reflux. Because the spinal medullary veins are not anatomically numerous, the presence of SDAVF is often associated with epidural veins congestion and thrombosis. That explains why the low-flow arteriovenous shunt of SDAVF induces a rises of venous pressure (74% of the mean arterial pressure) which leads to decreased arteriovenous gradient, segmental spinal cord edema that may progress into congestive ischemia and necrotizing myelopathy. Venous hypertension can be confirmed with angiography of the artery of Adamkiewicz by demonstrating severe prolongation of the venous phase. The caudo-cranial progression is favorized by a valveless venous system of the cord resulting in ‘arterialization’ of these veins with thickened and tortuous walls. The pressure in the draining vein also varies with arterial pressure and may lead to an exacerbation of symptoms. Because the SDAVFs is a slow-flow fistulae, hemorrhage is a rare clinical manifestation. Subarachnoid hemorrhage is rarely encountered especially in high cervical localization. Classification: Many classification systems were reported and changed over the time in the literature. Between 1971 and 2011, seven major classification systems have been enunciated based on the evolution of diagnostic methods and treatments for spinal AV shunts. The most used is the division of the vascular spinal lesions into SAVFs and SAVMs. SAVFs are further subdivided based on their extradural versus intradural location. The intradural SAVFs were divided in ventrally or dorsally due to their relation to the spinal cord. In turn, intradural ventral SAVFs are further divided into types A, B and C depending on the number and size of feeding branches. Extradural SAVFs represents direct connection between a branch of a radicular artery and the epidural venous plexus (figure 3). These are rare entities characterized by enlargement of epidural veins with medullary venous congestion that may cause compression of the spinal cord or nerve roots. More recently, these lesions are divided into; type A (SAVFs drain into both the epidural venous plexus and perimedullary venous plexus) and type B (SAVFs drain only into Batson’s plexus). Type B1 lesions compress the thecal sac due to an enlarged epidural venous plexus and type B2 lesions lack such compression. Intradural dorsal SAVFs are the most common type of spinal vascular malformation consisting in a direct connection between a dorsal spinal medullary artery and a medullary vein at the dural nerve root sleeve as shown in figure 4. Fig.4 SAVF: The connection between dorsal spinal medullary artery and medullary vein Fig.3 SAVF: The connection between radicular artery and the epidural venous plexus Bas J Surg, June, 24, 2018 65 Management of spinal dural arteriovenous fistula M El Husseini, H Mouawia, A Mrad & T Chaaban Progression of venous hypertension to the coronal venous plexus leads to venous congestion and progressive myelopathy. Intradural ventral SAVFs are typically high-flow direct fistulas between the ASA and coronal venous plexus. The lesions develops in the ventral subarachnoid space and can be further categorized into three subtypes according to their size; Type A fistulas, are singlefeeder lesions with slow blood flow and mild venous hypertension. Type B fistulas are progressively high-flow lesions with multiple minor feeders. Type C fistulas are usually large fistulas with a markedly enlarged venous drainage. Clinical symptoms: Patients with AVFs are typically older than 40 years. These AVFs occur much more frequently in males than in females. Most clinical reports showed a delay between the onset of clinical symptoms and diagnosis of these vascular lesions (between 12 and 44 months), largely due to nonspecific clinical presentation. The symptoms usually includes a combination of unilateral or bilateral lower extremity motor weakness that is worsening by intense movements. Gait disturbance, sensory symptoms (pain, paresthesias, diffuse or irregular sensory loss, hyperesthesia) and sphincter/bladder disturbances are also seen and commonly leads the clinicians to consider or exclude many other disorders before considering SDAVFs. Often misleading, mono or poly radiculopathy and low back pain are encountered and contribute to the difficulty of true diagnosis. Bowel and bladder incontinence, sexual dysfunction and urinary retention are seen late in the course the disease process. The symptoms are typically progressive and the natural evolution of untreated patients is to sever aggravation over a period of 6 months to 2 years. Spontaneous recovery has not been reported so far as sudden worsening has been more and more common. Misdiagnosis usually includes degenerative spine diseases, spinal cord tumours, neuromuscular diseases, peripheral vasculopathy or neurogenic claudication. Imaging Diagnosis: Typically, a spinal MRI is ordered as a first-line screening method for the evaluation of myelopathy and diagnosis of SDAVFs. On T2weighted sequences, the cord ed