Vascular Malformations of the Spinal Cord 

Updated: Feb 17, 2016
Author: James S Harrop, MD; Chief Editor: Brian H Kopell, MD 

Overview

Background

The spinal cord is composed of neuronal pathways, glial tissue, and interwoven vascular structures that perfuse the spinal parenchyma. Spinal cord vascular malformations (arterial and venous) represent a heterogenous group of blood vessel disorders that affect the spinal cord parenchyma either directly or indirectly. This group consists of spinal arteriovenous malformations (AVMs), dural arteriovenous fistulas (AVF), spinal hemangiomas, cavernous angiomas, and aneurysms. The focus of this article is the most prevalent spinal vascular malformations, AVMs and AVFs.

Spinal malformation. This is a sagittal T2-weighte 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.

AVMs and AVFs are rare disorders that may cause neurologic deterioration. An accurate diagnosis is important because these lesions may represent a reversible cause of myelopathy. Improvements in spinal cord imaging, such as MRI and angiography, have provided further insight into the anatomy and pathophysiology of these lesions. In addition, less-invasive treatment options such as neuroendovascular surgical approaches are presently being further explored.

In 1992, Anson and Spetzler classified spinal cord vascular malformations into the following 4 categories:[1]

  • Type 1: This dural AVF is the most common type of malformation, accounting for 70% of all spinal vascular malformations.[2] These fistulas are created when a radiculomeningeal artery feeds directly into a radicular vein, usually near the spinal nerve root. Dural AVFs are most commonly found in the thoracolumbar region.[3] Patients with type 1 malformations become symptomatic because the AVF creates venous congestion and hypertension, resulting in hypoperfusion, hypoxia, and edema of the spinal cord. Due to the slow-flow nature of type 1 AVFs, hemorrhage rarely occurs. Most dural AVFs are believed to occur spontaneously, but the exact etiology is still unknown.[3] Type I lesions are most frequently found in men between the fifth and eighth decades of life.

  • Type 2: Referred to as a glomus AVM, type 2 malformations consist of a tightly compacted group of arterial and venous vessels (nidus) inside a short segment of the spinal cord. Multiple feeding vessels from the anterior spinal artery and/or the posterior spinal circulation typically supply these AVMs. The abnormal vessels are intramedullary in location, although superficial nidus compartments can reach the subarachnoid space.[3] Type 2 AVMs are the most commonly encountered intramedullary vascular malformations, representing about 20% of all spinal vascular malformations. These lesions usually present in younger patients with acute neurologic deterioration secondary to their location, which is usually the dorsal cervicomedullary region. The mortality rate related to type 2 malformation is reported at 17.6%. After initial hemorrhage, the rebleed rate is 10% within the first month and 40% within the first year.

  • Type 3: These malformations are arteriovenous abnormalities of the spinal cord parenchyma fed by multiple vessels. These juvenile malformations are extensive lesions with abnormal vessels that can be both intramedullary and extramedullary in location. These lesions are typically found in young adults and children.

  • Type 4: Also known as pial AVFs, these malformations are intradural extramedullary AVFs on the surface of the cord that result from a direct communication between a spinal artery and a spinal vein without an interposed vascular network. They are usually seen in patients who are between their third and sixth decade of life.

Spinal vascular malformations can also be classified into 2 general groups. One group consists of the spinal dural fistulas (type 1), and the other group has intradural pathology (types 2-4).

Spinal dural arteriovenous fistulas (SDAVFs) are rare pathologies, with a yearly incidence of 5-10 new cases/million, constituting 60-80% of spinal arteriovenous malformations. Clinical symptoms include progressive paraparesis, paresthesias, bladder, and bowel disturbances.[4]

 

History of the Procedure

Spinal vascular malformations have been recognized as a potential cause of myelopathy for more than 100 years. In 1914, Charles Elsberg performed the first successful operation on a spinal cord malformation.

In the 1960s, significant advances were made in the techniques of spinal angiography, which produced further understanding of normal spinal vasculature and the pathophysiology of spinal cord malformations. Kendall and Loque used these modern imaging modalities to define a distinct subgroup of spinal AVMs classified as dural spinal AVFs. In 1977, Kendall and Loque treated these lesions with the less-invasive technique of directly ligating the fistula origin along the dural sleeve, with good results.[5]

The treatment of spinal cord malformations is being further expanded with the use of interventional neuroradiology. With further improvements in spinal angiography and endovascular techniques, these lesions may be embolized either as a primary treatment or as a complement to open microsurgical techniques.

Problem

Spinal vascular malformations consist of an abnormal connection between the normal arterial and venous pathways. These malformations do not benefit from intervening capillaries. As a result, venous pressure increases and the individual is predisposed to ischemia or hemorrhage.

Etiology

The etiology of vascular malformations of the spinal cord has not been clearly defined. Intradural parenchymal malformations arise in a younger patient population and are believed to be congenital. However, spinal arterial dural fistulas commonly arise in an elderly population and are believed to be due to a traumatic occurrence. These AVF malformations develop near a spinal dural artery, forming an abnormal arteriovenous communication with the venous circulation.

Pathophysiology

Spinal malformations can be separated into 2 subgroups.

The first subgroup is spinal AVFs, which are believed to be acquired lesions. They represent an abnormal connection between the spinal radicular artery and the medullary vein of the spinal cord. This fistula creates a slow-flow vascular malformation that typically develops over months to years. The high-pressure arterial flow from the radicular artery dilates the perimedullary venous system, causing venous stasis and hypertension. Venous hypertension results in a decreased arteriovenous gradient. The end result is venous outflow obstruction, hypoperfusion, and hypoxia of the spinal cord. Neurologic compromise is thought to occur secondary to this venous engorgement and to the resulting spinal cord ischemia.

The second subgroup is spinal intradural AVMs/AVFs, which are congenital lesions that consist of abnormal vasculature. These lesions recruit arterial blood vessels and have thin-walled venous vessels. Hemorrhage occurs when the high-flow arterial system overcomes the capacity of the abnormal venous vessels.

Presentation

Patient history and presentation are important factors in distinguishing spinal vascular malformations from other neurologic disorders. Patients with the more common dural AVF typically have presentations that are different from those of patients with intradural AVMs.

Typical characteristics of patients with dural AVF (type 1)

Patients with AVFs are typically older than 40 years. These AVFs occur much more frequently in males than in females. Symptoms increase over an extended period of months to years and include progressive weakness of the legs and concurrent bowel or bladder difficulties. Typically, pain is located in the distal posterior thoracic region over the spine, without a significant radicular component. However, painful radiculopathy may be present. Activity or a change in position may exacerbate symptoms in the thoracic or lumbar region and can result in thoracic spinal cord venous congestion and lower-extremity weakness.

These lesions can be mistakenly diagnosed as spinal stenosis and neurogenic claudication. The typical history of a patient with spinal claudication does not usually include lower-extremity weakness, but it can include a significant pain component similar to that of a spinal dural AVF.

Foix-Alajouanine syndrome is an extreme form of spinal dural AVF that affects a minority of patients. These patients present with a rapidly progressive myelopathy due to venous thrombosis from spinal venous stasis.

Typical characteristics of patients with intradural AVM (types 2-4)

The typical patient is younger than 30 years and presents with a subarachnoid or intraparenchymal hemorrhage, vascular steal phenomenon, and, rarely, mass effect on the spinal cord.

Patients with spinal intradural malformations typically present acutely either after intraparenchymal or subarachnoid hemorrhage. Patients with subarachnoid hemorrhage may experience sudden onset of a severe headache, meningismus, or photophobia. Acute subarachnoid hemorrhage with excruciating back pain is referred to as coup de poignard. A spinal AVM should be considered in the differential diagnosis of any patient with a subarachnoid hemorrhage who has negative cerebral angiography results.

If the hemorrhage is intraparenchymal, the patient presents with sudden neurologic deterioration, a sudden onset of pain, and a distinct spinal level of neurologic dysfunction. Rarely, patients present because of vascular steal phenomenon, in which oxygenated arterial blood shunted through the AVM causes the surrounding normal parenchyma to become hypoperfused.

Lastly, patients with intradural lesions can present with mass effect caused by growth of the AVM. The enlargement of the vascular malformation compresses the surrounding neural tissue, impairing neurologic function.

These intradural spinal vascular malformations (types 2-4) develop during embryogenesis and, therefore, are present in an even distribution throughout the spinal cord. Therefore, patients with intradural AVMs may present with upper- or lower-extremity difficulties, as opposed to patients with dural AVFs, who typically have only lower-limb–extremity involvement.

Physical examination findings and the type of spinal malformation are as follows:

  • Bruit over spinal cord - Intradural AVM

  • Hyperreflexia caudal to lesion - Dural AVF and intradural AVM

  • Upper motor signs - Dural AVF and intradural AVM

  • Weakness - Dural AVF and intradural AVM

  • Increased tone - Dural AVF and intradural AVM

  • Saddle region sensory disturbance - Dural AVF

  • Gait disturbances - Dural AVF

Relevant Anatomy

In order to understand and treat these arterial and venous malformations, knowledge of the normal spinal cord vascular supply is imperative. Unfortunately, the distribution of these spinal vessels is quite variable and inconsistent, but the major vessels are more consistent.

The aorta contributes to blood flow through the segmental arteries, which, in turn, supply the spinal medullary and radicular arteries. The radicular artery provides circulation to the nerve root dural sleeve. This is the artery typically involved in the formation of a spinal arteriovenous fistula (AVF) by its connection to the medullary spinal veins. This medullary artery bifurcates into anterior and posterior divisions, which then merge and form the spinal arteries. The spinal cord has 3 main spinal arteries (1 anterior and 2 posterior), which parallel the spinal cord.

The blood supply to the spinal cord can be divided into 3 anatomic regions:

  • The first is the cervicothoracic region, which receives segmental blood vessels from the vertebral arteries and the great vessels of the neck (ie, aorta, subclavian and carotid arteries).

  • The second is the midthoracic region, which receives most of its segmental blood supply from the aorta. This region of the spinal cord receives most of its blood supply from collateral circulation (superior and inferior arteries) and, therefore, is susceptible to infarction as a watershed area. For example, an aortic dissection or aortic atherosclerotic disease can send emboli to the anterior spinal artery (ASA); the patient presents with a sudden onset of painless lower-extremity paralysis with intact sensation. The spinal cord infarction affects the anterior motor portion because the ASA supply is lost but the posterior spinal arteries still perfuse the posterior spinal cord and sensory tracts.

  • The third is the thoracolumbar region, which receives segmental vessels from the abdominal aorta and the iliac arteries. The largest segmental vessel, the artery of Adamkiewicz, may be variably located between levels T9 and L2 and, in most cases, arises from the left side of the vertebral column.

The venous plexus in the spinal column, the Batson plexus, is unique compared with other venous plexuses in the body. This network of venous vessels does not have valves and thus does not prevent retrograde venous flow. Therefore, this valveless system allows an arterial fistula from the radicular artery to create congestion through the entire venous plexus, which can manifest as spinal cord ischemia.

Contraindications

Only relative contraindications exist for surgical obliteration of the fistula site, no absolute contraindications. Some of these relative contraindications include a hemodynamically unstable patient, active infection, and cardiac instability, among others.

 

Workup

Laboratory Studies

No laboratory studies are useful for the diagnosis of spinal cord vascular malformations. However, if the patient presents with symptoms of subarachnoid hemorrhage, a lumbar puncture or CT scan demonstrates blood in the spinal fluid.

Imaging Studies

Plain radiography is not usually helpful for diagnosis.

CT scanning may demonstrate dilated vessels in the thecal sac, but findings are usually normal. If a patient presents with symptoms of subarachnoid hemorrhage, CT scanning demonstrates blood in the spinal fluid.

Myelography findings, with or without CT, show dilated vessels in the intradural space. This imaging modality is very sensitive and shows these abnormalities in detail. This is an invasive procedure that requires injection of a contrast agent into the thecal sac. Postprocedure headaches are not uncommon.

MRI is a noninvasive imaging modality. The soft tissue and neural elements are visualized in detail with this technique. Dilated intradural vessels can be seen as flow voids or can be seen filling with contrast. Edema or hemorrhage in the spinal cord parenchyma can be assessed. The exact fistula site cannot be localized.

MRA or CTA are noninvasive modalities being used to identify any abnormal vessels. However, the resolution of these modalities is not to yet high enough.

Arteriography is the criterion standard modality for visualizing arteriovenous malformations (AVMs). This is a dynamic study that allows visualization of the pathology in real time, allowing assessment of high-flow versus low-flow AVMs. In addition, the location of the fistula can be visualized. Arteriography is an invasive procedure that may cause morbidity such as spinal cord ischemia, cerebral vascular accident, and vascular dissection.

Typically, a spinal MRI is ordered as a first-line screening method to detect spinal vascular malformations. If a spinal vascular malformation is still suspected, digital subtraction angiography (DSA) must be performed to display the very small vessels of the spinal cord. Owing to the complications involved with DSA, an MRA or CTA can be used to determine the spinal cord level of the feeding artery and thus limit the amount of time it takes to perform the DSA procedure.[6]

Diagnostic Procedures

If the patient presents with symptoms of subarachnoid hemorrhage, a lumbar puncture demonstrates blood in the spinal fluid.

 

Treatment

Medical Therapy

Presently, no acceptable pharmacological means are available to treat spinal vascular malformations.

The 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 adverse long-term affects. The 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

Each spinal vascular malformation is a unique lesion; therefore, an individualized treatment algorithm must be tailored to each patient. The present surgical treatment options include open surgical ligation or resection of the malformation, endovascular occlusion, spinal radiation, or a combination of these techniques.

Dural arteriovenous fistulas (AVFs), type 1, can be treated with either open or endovascular ligation. Both techniques yield excellent results, with occlusion rates reported as higher than 80%. The benefit of the endovascular technique is that it is less invasive. If the 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.[4, 7, 8, 9, 10, 11]

Intradural AVMs (types 2-4) are typically best treated with endovascular surgery and, if required, 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 demonstrated a lower incidence of recurrent hemorrhage; this may have a role in 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 material and microcatheters has made interventional treatment of spinal AVMs safer, with better results.[12, 13] 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 arteriovenous malformation (AVM) and reduces the risk of inadvertent embolization of normal vessels.

Liquid embolic agents are the first choice for most spinal AVMs because they are the most likely to fill distal nidus and because 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.[14]

The manipulation of viscosity of the liquid embolic as in the case of n-BCA or use of different viscosity Onyx (Onyx-18 versus Onyx-34) helps to ensure more precise deposition. Polymerization should occur in transit through the arteriovenous shunt. In higher-flow lesions, pharmacologically induced hypotension is used, typically with a mean arterial pressure of 50 mm Hg. With larger draining vessels, the Valsalva maneuver also 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. The advantages of PVA are that embolization may be performed at a more proximal location and that the size of particle can be determined depending on 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 choice of material used for embolization, all procedures should be performed under general anesthesia with neurophysiologic monitoring, depending on the location of the lesion. Somatosensory-evoked potentials (SSEPs) are very accurate in assessing spinal cord function. Motor-evoked potentials (MEPs) are also useful when a spinal AVM is supplied by the ASA.

Preoperative Details

The preoperative evaluation consists of a detailed neurologic examination, baseline urodynamic evaluation, and appropriate imaging studies that confirm the diagnosis of a vascular malformation. MRI of dural AVFs on the thoracolumbar junction usually shows serpiginous vessels in the intradural compartment, along with vasogenic edema in the spinal cord (see the images below). Intradural vascular spinal malformations appear as lesions in the spinal parenchyma.

Spinal malformation. This is a sagittal T2-weighte 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 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.

Once the diagnosis is considered, the anatomy of the malformation can be further defined with spinal arteriography. Spinal arteriography illustrates the detailed anatomy with dynamic images, providing the surgical team the information necessary to decide the best treatment option.

Intraoperative Details

Once the lesion has been defined and the surgical treatment plan (either endovascular, open surgical, or a combination of the two) is determined, the patient is taken to the operating room or endovascular suite. The procedure is performed with the patient under general anesthesia, with the use of neurophysiological 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, with either endovascular or an open technique to confirm closure of the fistula.

Recently, indocyanine green videoangiography has been used by some neurological surgery centers during the treatment of spinal dural AVFs. This new technology allows surgeons to view, in real time, the vasculature within the operating field to ensure the AVF has been obliterated.[15]

Postoperative Details

The patient is awakened from anesthesia and 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 in 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, an 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 MRIs for many months, even with successful treatment.[16]

Complications

Risks of open surgical or endovascular treatment

See the list below:

  • Skin infection or cellulitis

  • Bleeding

  • Injury to nervous tissue, causing paralysis, bladder or bowel dysfunction, or sexual dysfunction

  • Chronic pain syndromes

  • Thrombosis of epidural veins and neurologic loss

  • Recurrence of fistula

  • Spinal cord infarction

Complications that result from open surgical ligation or resection

See the list below:

  • Infection of meninges (meningitis)

  • Cerebrospinal fluid leak

  • Wound dehiscence

Complications that result from the endovascular technique

See the list below:

  • Femoral hematoma

  • Pseudoaneurysms and thrombosis

  • Arterial dissection

Outcome and Prognosis

Patient outcome is directly related to neurologic function at the time of the 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 a limited return of neurologic function.

Diagnosing these lesions early and providing appropriate treatment is important if patients are to achieve an optimal neurologic outcome.

Future and Controversies

MRI should be the first diagnostic modality performed when a spinal vascular malformation is suspected. If a lesion is found, spinal angiography is considered the criterion standard for optimal analysis of the angioarchitectural features. 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 of these lesions seems better than previously thought, especially with advances in endovascular techniques and new embolic agents that offer a high success rate with low morbidity.

Further advances in endovascular and microneurosurgical techniques will be made in the future. Advances in endovascular techniques and equipment should include smaller and more navigable catheters that can be manipulated through tortuous anatomy. The use of noninvasive techniques, such as stereotactic spinal radiosurgery, is presently being investigated.