Medical Therapy
There are nno acceptable pharmacologic means to treat spinal vascular malformations. Use of glucocorticoids may improve the patient's neurologic function for a short period. These steroids decrease vasogenic edema, but they do not treat the underlying pathology of the disorder. Unfortunately, these medications have long-term adverse effects. Prolonged use of steroids is associated with adverse systemic effects such as gastric ulceration, elevated blood glucose levels, and suppression of the immune system.
Surgical Therapy
Open surgical treatment
Each spinal vascular malformation is a unique lesion; therefore, an individualized treatment algorithm must be tailored to each patient. Surgical treatment options include open surgical ligation or resection of the malformation, endovascular occlusion, spinal radiation, and a combination of these techniques.
Dural arteriovenous fistulas (AVFs) can be treated via open or endovascular ligation. Both techniques yield excellent results, with occlusion rates higher than 80% reported. The benefit of the endovascular technique is that it is less invasive than the open surgical technique. If a patient has multiple sites of fistula formation, open ligation is more appropriate because all feeding vessels may be ligated under direct vision. Open surgery is necessary if the arterial feeding vessel is impossible to access because of tortuous vascular anatomy or if the vessel supplies blood to healthy regions of the spinal cord. [16, 17, 18, 19, 20, 21]
Intradural AVMs typically are best treated via endovascular surgery and, if required, by open surgery and resection.
Endovascular treatment
Treatment options are dictated by the location of the lesion, the patient's medical condition, and the risk-versus-benefit ratio. The most important factor in determining treatment options is the presence of intramedullary or extramedullary shunting. Malformations that are subpial in location are less likely to be cured. These are usually supplied by subcommissural branches of the anterior spinal artery (ASA). The role of partial embolization is not clear. Long-term clinical results in patients with symptomatic spinal AVMs have included a lower incidence of recurrent hemorrhage; this may have a role in treatment of difficult lesions. Lesions on the surface of the spinal cord that are supplied by circumferential branches of the ASA may be safely treated with either embolization or surgery.
The new generation of liquid embolic materials and microcatheters has made interventional treatment for spinal AVMs safer, yielding better results. [22, 23] The goal of any intervention is to eliminate the shunt. Microcatheterization is of paramount necessity in achieving effective results. Delivery of embolic material to the nidus of the lesion reduces the AVM and lowers the risk of inadvertent embolization of normal vessels.
Liquid embolic agents are the first choice for treatment of most spinal AVMs because they are most likely to fill the distal nidus and they are associated with a low recanalization rate. The authors' agents of choice are n-butyl cyanoacrylate (n-BCA) and Onyx (ethylene vinyl alcohol copolymer). Embolization of lesions supplied by the ASA requires selective catheterization and deposition of embolic material. Permanent deficits due to embolizations in the ASA territory occur in up to 11% of patients. [24]
Manipulation of the viscosity of the liquid embolic material as in the case of n-BCA or use of different viscosity Onyx (Onyx-18 vs Onyx-34) helps to ensure more precise deposition. Polymerization should occur in transit through the arteriovenous shunt. For higher-flow lesions, hypotension is pharmacologically induced, typically with a mean arterial pressure of 50 mm Hg. With larger draining vessels, the Valsalva maneuver helps to delay transit time.
When preoperative embolization is planned, polyvinyl alcohol microparticles (PVAs) are a reasonable choice of embolic material. They are also useful for embolization of type 2 AVMs. Advantages of PVAs are that embolization may be performed at a more proximal location and the size of the particles can be determined according to the size of the lesion and its collaterals. The goal of treatment with either agent is to provide distal occlusion of the nidus. Proximal occlusion results in collateral reconstitution, with little hope of cure.
Regardless of the material chosen for embolization, all procedures should be performed with the patient under general anesthesia with neurophysiologic monitoring, depending on the location of the lesion. Somatosensory-evoked potentials (SSEPs) are highly accurate in assessing spinal cord function. Motor-evoked potentials (MEPs) are useful when a spinal AVM is supplied by the ASA.
Preoperative, Intraoperative, and Postoperative Details
Preoperative
Preoperative evaluation consists of a detailed neurologic examination, a baseline urodynamic evaluation, and appropriate imaging studies that confirm the diagnosis of a vascular malformation. Magnetic resonance imaging (MRI) of dural AVFs at the thoracolumbar junction usually shows serpiginous vessels in the intradural compartment, along with vasogenic edema in the spinal cord. Intradural vascular spinal malformations appear as lesions in the spinal parenchyma.
Once the diagnosis is considered, the anatomy of the malformation can be further defined with the use of spinal arteriography. Spinal arteriography illustrates detailed anatomy through dynamic images, providing the surgical team with the information necessary to decide the best treatment option.
(See the images below.)
Spinal malformation. This is a sagittal T2-weighted MRI of the thoracic spine of a 68-year-old woman with a 9-month history of back pain and sensory loss, progressing to the point of loss of bowel and bladder function along with a sudden onset of paraparesis. Note the thoracolumbar junction with an edematous spinal cord and dilated serpiginous intradural venous plexus.
Spinal malformation. This is an axial T2-weighted MRI of the thoracic spine of a 68-year-old woman with a 9-month history of back pain and sensory loss, progressing to the point of loss of bowel and bladder function along with a sudden onset of paraparesis. Note the lumbar spine with an edematous spinal cord and dilated intradural venous plexus.
Intraoperative
Once the lesion has been defined and the surgical treatment plan (endovascular, open surgical, or a combination of the two) has been determined, the patient is taken to the operating room or to the endovascular suite. The procedure is performed with the patient under general anesthesia with the use of neurophysiologic monitoring. Intraoperative monitoring allows analysis of ischemia to the spinal cord, so that normal vascular channels are not inadvertently permanently disturbed. Arteriography may be performed in the operating room via an endovascular or an open technique to confirm closure of the fistula.
Indocyanine green videoangiography has been used at some neurologic surgery centers during treatment of spinal dural AVFs. This technology allows surgeons to view, in real time, the vasculature within the operating field to ensure that the AVF has been obliterated. [25]
Postoperative
When surgery has been completed, the patient is awakened from anesthesia and is taken to a monitored setting, where serial neurologic examinations can be performed. With ligation of the dural AVF, most patients show neurologic improvement and can begin physical therapy. Improvement in neurologic examination findings may take several weeks. If arteriography was not performed in the operating room, it should be performed during the immediate postoperative period to document closure of the fistula.
Follow-up
Patients should be monitored with serial neurologic examinations and imaging studies in an outpatient setting to confirm closure of the fistula. With intradural lesions, a procedure is deemed successful based on intraoperative assessment of complete resection and a postoperative arteriogram that shows no arteriovenous shunting. If patients experience any worsening from their neurologic baseline, appropriate evaluation with imaging studies is completed to rule out fistula recurrence.
Postoperative MRI findings do not necessarily correlate with clinical outcomes. It is not uncommon for spinal cord abnormalities to persist on MRI for many months, even when treatment is successful. [26]
Complications
Open surgical or endovascular treatment
Risks of this procedure include the following:
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Skin infection or cellulitis
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Bleeding
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Injury to nervous tissue, causing paralysis, bladder or bowel dysfunction, or sexual dysfunction
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Chronic pain syndromes
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Thrombosis of epidural veins and neurologic loss
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Recurrence of fistula
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Spinal cord infarction
Open surgical ligation or resection
Complications include the following:
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Infection of meninges (meningitis)
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Cerebrospinal fluid leak
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Wound dehiscence
Endovascular technique
The following complications have been noted:
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Femoral hematoma
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Pseudoaneurysm and thrombosis
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Arterial dissection
Outcome and Prognosis
Vascular disorders of the spine are more rare than cerebral vascular entities but can result in significant morbidity. [2] Prompt recognition and timely management of vascular disorders of the spinal cord can improve patient outcomes. [27] Advances in neurovascular imaging, along with increased utilization of these advances, have resulted in more frequent and timely identification of these lesions. [1] Treatment modalities include endovascular and surgical therapy. Endovascular treatment offers the advantages of a less invasive approach; therefore, it is usually chosen as primary therapy. [10]
Favorable safety profiles and cure rates can be achieved with appropriate patient selection and judicious use of different treatment modalities. [28] Surgery and, to a lesser extent, stereotactic radiosurgery are used when endovascular approaches are impossible or have proved unsuccessful. [29]
Typically, the clinical presentation of a spinal vascular malformation is insidious, and patients' symptoms are regularly attributed to other conditions. Although previous studies have characterized neurologic outcomes after treatment for these lesions, little is known about the pretreatment patient characteristics associated with poor and/or positive patient outcomes. Misdiagnosis has been relatively common among patients with spinal vascular malformation and has contributed to delays in treatment, which appear to be associated with worse clinical outcomes for patients who, ultimately, do receive treatment. [30]
Patient outcome is directly related to neurologic function at the time of surgical intervention. Patients who are able to ambulate when treated tend to remain ambulatory and may increase their strength with physical therapy. Patients who do not have antigravity strength in the lower extremities before treatment are unlikely to regain neurologic function to the point of ambulation. Patients who present with bowel or bladder dysfunction have limited return of neurologic function.
Diagnosing these lesions early and providing appropriate treatment are important if patients are to achieve optimal neurologic outcomes.
Future and Controversies
Magnetic resonance imaging (MRI) should be the first diagnostic modality used when a spinal vascular malformation is suspected. If a lesion is found, spinal angiography is considered the criterion standard for optimal analysis of angioarchitectural features.
With rapid advancements in endovascular therapy, treatment for spinal arteriovenous malformations (AVMs) continues to evolve. The decision to use endovascular versus surgical therapy largely depends on the type of lesion identified and its anatomic location. Studies have shown that endovascular treatment is effective for extradural arteriovenous fistulas (AVFs), intradural ventral (perimedullary) AVMs, and intramedullary spinal AVMs. Surgery and, to a lesser extent, stereotactic radiosurgery are used when endovascular approaches are impossible or have proved unsuccessful. [29] Extradural-intradural (juvenile) AVMs and conus AVMs remain difficult-to-treat lesions. [30, 31]
Spinal AVMs are rare disorders with a low prevalence; treatment for patients with this complex diagnosis usually requires the collaboration of professionals from several neuroscience disciplines. [32] Because delayed initial diagnosis leads to irreversible damage of the spinal cord, neurosurgeons should always include spinal AVM in the the differential diagnosis. [8]
Embolization with a liquid embolic agent is the first-choice treatment for type 2-4 malformations, whereas surgery may be a better option for type 1 malformations. The prognosis for patients with these lesions seems to be better than was previously thought, especially with advances in endovascular techniques and available embolic agents that offer a high success rate with low morbidity.
Further advances in endovascular and microneurosurgical techniques should include smaller, more navigable catheters that can be manipulated through tortuous anatomy.
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Spinal malformation. This is a sagittal T2-weighted MRI of the thoracic spine of a 68-year-old woman with a 9-month history of back pain and sensory loss, progressing to the point of loss of bowel and bladder function along with a sudden onset of paraparesis. Note the thoracolumbar junction with an edematous spinal cord and dilated serpiginous intradural venous plexus.
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Spinal malformation. This is an axial T2-weighted MRI of the thoracic spine of a 68-year-old woman with a 9-month history of back pain and sensory loss, progressing to the point of loss of bowel and bladder function along with a sudden onset of paraparesis. Note the lumbar spine with an edematous spinal cord and dilated intradural venous plexus.
