Review Article

Vascular Myelopathies Alejandro A. Rabinstein, MD, FAAN ABSTRACT Purpose of Review: Vascular myelopathies include several diagnoses that are often misdiagnosed or undertreated. Some represent neurologic emergencies, such as spinal cord infarction, and others can be disabling if they remain unrecognized, such as spinal dural arteriovenous fistulas. This review describes the clinical characteristics and current therapeutic strategies for the most common vascular myelopathies and emphasizes practical concepts for the clinician. Recent Findings: Although none of the vascular myelopathies have been studied in large prospective studies and their treatments have not been tested in randomized controlled trials, recent years have brought advances in diagnostic imaging and treatment alternatives as well as useful information regarding prognosis. Refinement in MRI technique now allows precise, noninvasive diagnoses of most vascular myelopathies and is crucial for the exclusion of differential diagnoses. Surgical and endovascular therapies are highly effective in treating spinal vascular malformations. Longitudinal studies have shown that the prognosis of spinal cord infarction is more favorable than previously conceived, and even patients with severe deficits can achieve meaningful recovery. Summary: Clinicians should be keenly aware of the clinical and radiologic features of the various vascular causes for acute or progressive myelopathy. Optimal management of patients with vascular myelopathies requires close collaboration with neuroradiologists, neurointerventionalists, and vascular neurosurgeons. Prognosis should be estimated with caution because functional outcomes over time may be better than initially expected. Vascular myelopathies are infrequent, but their consequences to the patient’s functional capacity can be devastating. Because of their relative rarity, these disorders are often initially misdiagnosed, and, in some cases, this delay in arriving at the correct diagnosis can prove very detrimental. This article reviews the essential concepts of diagnosis and management of vascular diseases of the spinal cord, both ischemic and hemorrhagic, beginning with a basic summary of the vascular anatomy of the cord, as this knowledge is crucial for an understanding of the pathologies.

Address correspondence to Dr Alejandro A. Rabinstein, Mayo Clinic, Department of Neurology, W8B, 200 First Street SW, Rochester, MN 55905, [email protected]. Relationship Disclosure: Dr Rabinstein receives a grant from DJO Global, Inc, and receives royalties from Elsevier and Oxford University Press. Unlabeled Use of Products/Investigational Use Disclosure: Dr Rabinstein reports no disclosure. * 2015, American Academy of Neurology.

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VASCULAR ANATOMY OF THE SPINAL CORD The spinal cord is supplied by three main longitudinal arteries: the anterior spinal artery and the two smaller posterior spinal arteries. The anterior spinal artery is located along the ventral midline of the cord and supplies the anterior two-thirds of the cord tissue by branching into left and right intramedullary arteries, known as sulcocommissural arteries. The posterior spinal arteries lie on each side of the posterior aspect of the cord and Continuum (Minneap Minn) 2015;21(1):67–83

supply its posterior third. Thus, the anterior, central, and lateral regions of the cord are irrigated by the anterior spinal artery, and the dorsal horns and columns receive blood from the ipsilateral posterior spinal artery. An intramedullary watershed area can be found in the central cord between small penetrating branches from the anterior and posterior spinal arteries. Branches from the three spinal arteries encircle the surface of the cord, forming a fine pial plexus with multiple anastomoses (known as the vasocorona). www.ContinuumJournal.com

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Vascular Myelopathies KEY POINTS

h The anterior, central, and lateral regions of the cord are perfused by the anterior spinal artery and the dorsal horns and columns from the ipsilateral posterior spinal artery.

h Abdominal aorta disease and aortic surgery are the most common causes of spinal cord infarction in daily practice.

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The anterior spinal artery originates from the vertebral arteries in the cervical region and from radicular arteries in the thoracic and lumbar regions. Often, the anterior spinal artery forms at the upper cervical level by the joining of two branches, each arising from the V4 segment of the vertebral artery; however, many anatomical variations exist, and these branches may occasionally arise from the posterior inferior cerebellar arteries or from cervical segmental branches. Meanwhile, just a few radicular arteries are responsible for the blood supply to the spinal arteries at the thoracolumbar level. These radicular arteries stem from segmental branches of the aorta (posterior intercostal and lumbar branches) that reach the intervertebral foramina and divide into the anterior and posterior radicular arteries. The largest radicular artery is the arteria radicularis magna of Adamkiewicz (or main anterior radicular artery), which most commonly arises on the left from T9 to T12, but occasionally can be positioned on the right (in 17% of cases) and arise anywhere from T5 to L3. Between the lower cervical and the mid- to lower thoracic levels, there are usually just two or three small radicular branches supplying this long portion of the cord. Hence, the midthoracic area is traditionally considered a watershed territory at high risk for ischemia from hypoperfusion. Yet, most cases of documented spinal cord ischemia do not occur in this area.1,2 The venous system consists of radially oriented intramedullary veins that drain into the unpaired anterior and posterior median spinal veins and into an extramedullary circumferential network known as the coronal plexus. There are typically 10 to 20 radiculomedullary and radiculopial veins that arise from the anterior and posterior median spinal veins, respectively. These veins exit the dural space to form the valveless, circumferential, longitudinally continuous epidu-

ral venous plexus. Figure 4-13 illustrates the vascular anatomy of the spinal cord. SPINAL CORD INFARCTION It is often quoted that spinal cord infarctions represent 1% of all strokes and 5% to 8% of acute myelopathies,4 but their precise incidence is unclear, and the likelihood of their occurrence varies greatly with the clinical situation. Spinal cord infarctions can have multiple causes, but aortic surgery is by far the most common (Table 4-1).1,2 Paraplegia from a spinal cord infarction is the most frequent neurologic complication after thoracic aneurysm repair, either with open surgery or endovascular therapy.5 Nonaortic surgery in patients with multiple vascular risk factors or advanced vascular disease, aortic dissection, and prolonged severe hypotension (including cardiac arrest) are well-recognized causes of spinal cord infarction.2 Cases of spinal cord infarction unrelated to surgical intervention often remain cryptogenic. Perhaps more common than usually appreciated, fibrocartilaginous embolism may account for up to 5% of cases of spinal cord infarction and is caused by the embolization of fragments of the nucleus pulposus, often related to minor trauma, lifting, or physical exertion, most commonly in young women.6 The peak incidence of spinal cord infarction is between the sixth and seventh decades, largely driven by postoperative cases. 2,7,8 MRI showing cord swelling with a prolapsed disk space at the appropriate level may signal the diagnosis of fibrocartilaginous embolism in the correct clinical setting.9 Clinical Presentation The diagnosis of spinal cord infarction is primarily clinical. Ischemia typically affects the anterior spinal artery territory. Patients present with sudden flaccid paralysis (paraplegia or quadriplegia

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FIGURE 4-1

Graphic illustration of the vascular anatomy of the spinal cord in longitudinal (A) and axial (B) views. Reprinted with permission from Rabinstein AA, Resnick SJ, Saunders Elsevier.3 B 2009 Elsevier, Inc.

depending on the level of the ischemia), areflexia, loss of sensation to pain and temperature (ie, spinothalamic sensory modalities), and autonomic deficits (such as atonic bladder/urinary retention, paralytic ileus, and abolished sphincter tone) below the level of the lesion (Table 4-2). The progression to maximal weakness can occur over a few hours in cases of spinal cord infarction from fibrocartilaginous embolization.6 Posterior column sensory modalities (vibration and proprioception) are characteristically preserved, resulting in dissociated sensory loss. However, during the first few hours it is not infrequent for patients with severe spinal cord ischemia to be unable to feel vibration or changes in joint position, which may raise suspicion for epidural spinal cord compression. Back or radicular pain may be severe at the site of infarction, but it is Continuum (Minneap Minn) 2015;21(1):67–83

an inconsistent (present in approximately one-third of patients) and often shortlasting and self-limited symptom. After the acute phase, pyramidal signs (eg, spasticity, hyperreflexia, Babinski signs, clonus) may develop in patients with less severe infarction. The most common location of spinal cord infarction is the lower thoracic cord, and the most frequently encountered sensory level is at T10.2 Cervical spinal cord infarction occurs much less often, but is particularly severe. When involving the upper cervical cord, spinal cord infarction can present with respiratory failure. Other infrequent clinical presentations include the following syndromes: (1) posterior spinal artery territory infarction, which involves severe loss of proprioception with relative preservation of motor function; (2) transverse cord infarction, which involves

KEY POINT

h Acute spinal cord ischemia manifests with flaccid, areflexic paralysis with loss to pain and temperature sensations below the level of the ischemic insult.

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TABLE 4-1 Causes of Spinal Cord Infarction b Aortic dissection b Aortic surgery b Aortic atherosclerosis b Severe hypotension b Spinal trauma b Fibrocartilaginous embolism b Cardiogenic embolism b Subclavian artery dissection b Vertebral artery dissection b Vasculitis b Decompression sickness b Other iatrogenic causesa b Other various causesb b Cryptogenic a

Other iatrogenic causes include nonaortic surgery, vertebral angiography, celiac plexus neurolysis, renal artery embolization, intraaortic balloon-pump counterpulsation, and intrathecal injection of lidocaine or phenol, among others. b Other various causes include sickle cell disease, cancer, and other hypercoagulable disorders.

flaccid weakness, local pain, and loss of all sensory modalities and autonomic control below the level of the lesion; (3) Brown-Se´quard, which involves ipsilateral flaccid weakness and contralateral loss of pain and temperature sensation, likely resulting from sulcocommissural artery occlusion; and (4) centrospinal infarction, which involves persistent lower motor neuron weakness and dissociated loss of pain and temperature sensation in a segmental distribution caused by ischemic injury of the central gray matter of the cord. Typically seen after trauma, centrospinal infarction can be partially reversible, with recovery of leg strength and persistent weakness of the arms, in a pattern often referred to as man-in-the-barrel syndrome.7 Transient attacks of spinal cord ischemia are quite rare. When appearing

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along with sudden drops in perfusion pressure, they should prompt evaluation of the aorta and vertebral arteries. Exertional claudication can be a manifestation of spinal cord ischemia from venous hypertension in patients with a spinal dural arteriovenous fistula. Radiologic Findings CT may be useful to exclude alternative diagnoses, most notably cord compression from an epidural hematoma. Yet, CT cannot confirm the presence of spinal cord infarction. Therefore, MRI is the diagnostic modality of choice when spinal cord infarction is suspected.10,11 Most useful are the T2-weighted and fluid-attenuated inversion recovery (FLAIR) sequences, which show a pencil-like hyperintense signal on sagittal cuts, often with associated cord enlargement from ischemic swelling (Figure 4-2A). On axial images, the TABLE 4-2 Classical Clinical Features of Spinal Cord Infarction (Anterior Spinal Artery Syndrome) b Flaccid weakness below the lesion (paraplegia or quadriplegia) b Anesthesia or hypoesthesia to pain and temperature below the lesiona b Urinary retention (atonic bladder) b Constipation (paralytic ileus) b Areflexia below the lesion b Absent rectal tone b Preservation of proprioception and vibration (usually) b Back or radicular pain at the level of the lesion b Respiratory failure (with rare midcervical and uppercervical infarctions) a

Pinprick level typically present.

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FIGURE 4-2

MRI demonstration of spinal cord infarction on sagittal (A) and axial (B) T2-weighted sequences. Arrows indicate the signal in the areas of ischemia.

infarction takes the appearance of ‘‘owl eyes’’ (Figure 4-2B), reflecting the preferential involvement of the ventral gray matter. The changes are fairly symmetric and almost always bilateral. Increased bone marrow signal may indicate concurrent bone infarction. Diffusion-weighted imaging may demonstrate acute ischemia before the infarction becomes visible on other sequences.12 Yet, the sensitivity of diffusion-weighted imaging in the spinal cord is lower than in the brain because of higher susceptibility to image distortion. Multishot, interleaved echo planar imaging may be used to improve the quality of diffusion-weighted imaging. Enhancement on postgadolinium images may appear a few days after the onset of symptoms. The sensitivity of MRI for the diagnosis of spinal cord ischemia is not well established. Differences in time to obtain the MRI, the sequences obtained, quality of the studies, and certainty of the clinical diagnosis may explain the divergence of sensitivity rates reported across different series. The reliability of MRI for the demonstration of spinal cord infarction can be compromised by motion, pulsatility, and susceptibility artifacts. Therefore, absence of definite Continuum (Minneap Minn) 2015;21(1):67–83

evidence of infarction on MRI cannot completely exclude the diagnosis of spinal cord infarction, especially early after symptom onset. Spinal angiography is usually not performed in patients with suspected or documented spinal cord infarction, unless it is presumed to be related to a spinal dural arteriovenous fistula. Noninvasive angiography (ie, CT angiography (CTA) or magnetic resonance angiography [MRA]) can be useful when it is deemed necessary to exclude aortic dissection. Differential Diagnosis A compressive epidural hematoma is the main alternative diagnosis and should be particularly considered in patients with acute paraplegia or quadriplegia after surgery, especially after exposure to anticoagulation. CT scan can be sufficient to rule out a hematoma, but it is crucial that the quality of the images leaves no room for doubt. Postoperative cases of cervical spinal cord compression from epidural hematoma have occurred in which the diagnosis was initially dismissed because of a seemingly reassuring, but suboptimal CT scan. Because a diagnostic delay may make a major difference www.ContinuumJournal.com

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Vascular Myelopathies KEY POINT

h Treatment of spinal cord ischemia consists of trying to improve cord perfusion using vasopressors for hemodynamic augmentation and lumbar drain for CSF decompression.

in the chances of functional recovery after surgical evacuation for a patient with cord compression from an acute h e ma t o m a , e m e r g e n c y M R I i s warranted in this situation. Diagnostic testing in addition to imaging of the spinal cord should be individualized. Noninvasive angiogram of the aorta and cervical vessels (the latter in cases of cervical spinal cord infarction) are useful to evaluate for dissection. CSF analysis may be necessary to exclude infectious or inflammatory myelopathies (the fluid is normal in most cases of spinal cord infarction).2 Additional investigations to consider in selected cases include serum B12 and homocysteine concentrations, serum markers of systemic inflammation and vasculitis, neuromyelitis optica antibody (NMO IgG), paraneoplastic antibody panel, peripheral blood smear, and hypercoagulability panel. Treatment The treatment of spinal cord infarction consists of trying to improve cord perfu-

sion through collateral flow. This can sometimes be achieved by the combination of hemodynamic augmentation and lumbar drainage.13 Vasopressors are used to increase perfusion pressure, while CSF is removed to reduce the resistance to microcirculatory flow. These acute treatments have not been adequately tested, but attempting them is advisable because some patients can have dramatic improvement (Case 4-1). Lumbar drainage, hypothermia, and strict avoidance of hypotension are commonly used strategies during aortic aneurysm surgery.14 Neuroprotectants administered before aortic surgery are being tested, but none are available for use at present. No recanalization therapy has been formally tested in spinal cord infarction. Very few cases treated with IV thrombolysis have been reported, and this treatment is contraindicated in patients with aortic dissection and in the immediate postoperative period after a major vascular surgery. Avoiding hypoglycemia, treating moderate and severe

Case 4-1 A 72-year-old man with multiple vascular risk factors was admitted with acute abdominal aortic aneurysm rupture and underwent emergent surgical repair of the aorta. When he woke in the intensive care unit, it was noted that he could not move his legs, and the neurology service was immediately consulted. Examination showed flaccid paraplegia with a sensory level to pinprick at T9-T10, with anesthesia to pain and temperature below that level. His blood pressure at the time of his neurologic consultation was 90/60 mm Hg. He was started on hemodynamic augmentation with norepinephrine, and a lumbar drain was emergently inserted in the thecal space. After these interventions, the patient experienced partial improvement, regaining some movement of the legs and nearly full sensation. The patient was gradually weaned from the vasopressor after 2 days, and the lumbar drain was removed on day 3 without recrudescence of symptoms. The patient was discharged to a rehabilitation facility still wheelchair dependent and with a bladder catheter, but 1 year later he was able to walk with a walker and control his micturition. Comment. Strict neurologic monitoring is crucial after any abdominal aortic surgery. Early detection of spinal cord ischemia should prompt emergency treatment with hemodynamic augmentation using vasopressors and CSF decompression by means of a lumbar drain (which may already be in place in cases of elective surgery). These combined interventions, although not formally tested, sometimes can be quite effective in reversing neurologic deficits. When it occurs, the reversal is usually partial but may be sufficient to improve the prognosis. Even patients with very severe deficits at onset can improve over time and regain meaningful function.

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hyperglycemia, and maintaining normothermia are reasonable objectives, although the value of these interventions has not been examined. Corticosteroids do not have a role in the treatment of spinal cord infarction unless caused by vasculitis. Induced hypothermia has been proposed but its value remains unproven. Hyperbaric oxygen therapy is recommended for patients with spinal cord decompression sickness.15 Patients with spinal cord infarction are at high risk of secondary systemic complications, especially venous thromboembolism, urosepsis, and pressure ulcers. Aspiration pneumonia and autonomic dysreflexia are additional threats for patients with cervical spinal cord infarction. The same precautions that are applied in cases of traumatic spinal cord injury should be implemented for the care of patients with spinal cord infarction. For more information, refer to the article ‘‘Management of Acute Spinal Cord Injury’’ by Deborah M. Stein, MD, MPH, FACS, FCCM, and Kevin N. Sheth, MD, FAHA, FCCM, FNCS, in this . issue of Prognosis Spinal cord infarction can be severely incapacitating and even fatal. Yet, substantial, functional improvement over time is possible.2,7,8 The prognosis of spinal cord infarction depends primarily on the severity of the neurologic deficits at nadir.2 Nearly complete motor and sensory loss (American Spinal Injury Association [ASIA] grades A and B), bladder dysfunction, or abolished proprioception at onset predict worse long-term outcome.8,10 However, the prognosis of spinal cord infarction in patients with more benign presentations may be much more favorable.2,7,8 Other factors reported to portend poorer prognosis, albeit less consistently, are older age,8 female sex,8 and more extensive ischemic changes on MRI.2 Conversely, presContinuum (Minneap Minn) 2015;21(1):67–83

ence of Babinski signs upon diagnosis may indicate better chances of recovery.2 When prognosticating in patients with spinal cord infarction, highlighting the possibility of meaningful, functional recovery over time is important. Even some patients with severe impairment at onset may achieve substantial recovery.2,10 In a study of the long-term outcomes of 115 consecutive patients with spinal cord infarction, we found that after a mean follow-up of 3 years, the mortality rate was high (23%), but substantial functional improvement was not uncommon.2 Among patients discharged using a wheelchair, 41% were walking by the last follow-up. Of those who required bladder catheter at hospital dismissal, 33% were catheter-free at last follow-up. SPINAL DURAL ARTERIOVENOUS FISTULA Spinal dural arteriovenous fistulas are abnormal direct connections between a radicular feeding artery and a radiculomedullary vein, which, in turn, retrogradely fills the coronal plexus around the spinal cord. The fistula is located in the dural sleeve of the nerve root. Shunting of arterial blood flow causes venous congestion, venous hypertension, and, consequently, progressive myelopathy.16,17 Venous infarction with permanent cord damage can occur if the fistula is not treated in a timely manner. Spinal dural arteriovenous fistulas constitute more than 70% of spinal arteriovenous malformations (AVMs) (Table 4-3).18,19 They are thought to be acquired anomalies, unlike intramedullary AVMs, and are found predominantly in men, although the reason for this sex predilection is unknown. The peak incidence of spinal dural arteriovenous fistula diagnosis is in the sixth and seventh decades, and the most frequent location of the fistula is the lower thoracic

KEY POINTS

h The prognosis of spinal cord infarction depends primarily on the maximal severity of the neurologic deficits.

h Meaningful functional recovery is possible over time in patients with spinal cord infarction, even among those with severe deficits during the acute phase.

h Spinal dural arteriovenous fistulas result from the direct connection of a radicular artery with a radiculomedullary vein in the dural sleeve of a nerve root. They cause myelopathy from venous congestion and cord edema.

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TABLE 4-3 Classification Schema of Spinal Arteriovenous Malformations Study

Characteristics 18

Anson and Spetzler, 1993 Type I spinal arteriovenous malformation (AVM)

Dural arteriovenous fistulaa

Type II spinal AVM

Intramedullary glomus AVMa

Type III spinal AVM

Juvenile, extramedullary, and extradural AVMs

Type IV spinal AVM

Perimedullary AVM

Spetzler et al, 200219 Arteriovenous fistulas Intradural Dorsal

Radicular artery with medullar veinb

Ventral

Anterior spinal artery with coronal venous plexusc

Extradural

Radicular artery with epidural venous plexusd

AVMs Intramedullary Extradural-intradural Conus medullaris a b c d e

Glomus AVM with nidus in the cord e

Juvenile AVM Nidus in the pia of the conus or cauda equina

Dural arteriovenous fistulas (70% to 75%) and intramedullary glomus AVMs (15% to 20%) represent the vast majority of spinal arteriovenous malformations. Fistula located at the nerve root sleeve; most common form of spinal vascular malformation. Fistula located in the ventral subarachnoid space. Some arteriovenous fistulas also drain into the perimedullary venous plexus. Patients with cutaneomeningospinal angiomatosis (Cobb syndrome) and perhaps those with Klippel-Trenaunay-Weber syndrome may be included in this category.

to upper lumbar level.19 The resultant venous hypertension affects the entire cord below the level of the fistula. Cervical spinal dural arteriovenous fistulas are rare. Clinical Presentation The clinical presentation of spinal dural arteriovenous fistulas is fairly characteristic despite lacking any pathognomonic signs or symptoms (Table 4-4). Symptoms of myelopathy usually start insidiously and progress gradually, but more rapid progression is possible. Up to one-fourth of patients may have defined episodes of neurologic decline, and a very small minority present acutely with significant deficits.16 Weakness and sensory symptoms in the legs are the most common initial

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manifestations of the disease.20,21 These symptoms are not infrequently asymmetric at their onset, but become bilateral and fairly symmetric over time. The leg weakness typically worsens with exertion (exertional claudication) and improves with rest.20 More advanced cases may exhibit worsening with prolonged standing and relief with recumbency. Pain in the back or legs occurs in at least 20% of patients at presentation and in a larger proportion over the course of the disease and may mimic a radiculopathy.16 Ascending paresthesia and dysesthesia in the legs can be wrongly ascribed to peripheral neuropathy.16 Sphincter problems (urinary and fecal retention or incontinence) and erectile dysfunction are rare early but very commonly present by the time of

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TABLE 4-4 Clinical Features of Spinal Dural Arteriovenous Fistula b Leg weakness (asymmetric but bilateral)a b Exertional claudication b Decreased sensation in the legs (all modalities)b b Back and radicular pain b Leg paresthesia and dysesthesia (sometimes ascending) b Perineal hypoesthesia b Erectile dysfunction b Urinary retention or incontinence b Constipation or fecal incontinence a

Can have pattern of upper motor neuron, lower motor neuron, or a combination of both. b Pinprick level is inconsistently present.

diagnosis. Cervical spinal dural arteriovenous fistulas can present with arm involvement and, exceptionally, with respiratory impairment. Examination shows a pinprick level in over one-third of patients.20 This finding is more common in patients with extensive cord involvement. The most frequent location of the level is between T10 and L1, but it does not correlate reliably with the site of the fistula.20 Sensory examination may also reveal loss of vibratory and proprioceptive sensation, a stocking pattern of hypoesthesia to pain and temperature, and perineal hypoesthesia. The pattern of weakness may be upper motor neuron, lower motor neuron, or both.16,20 Radiologic Findings The diagnosis of spinal dural arteriovenous fistula can be reliably made with noninvasive imaging of the spine. MRI can be highly sensitive and specific for this condition, but clinical suspicion is crucial in maximizing the Continuum (Minneap Minn) 2015;21(1):67–83

yield of the study. Scanning should encompass the entire cord because the physical examination cannot localize the level of the fistula. Cord edema or ischemia from the effects of venous hypertension manifests as a longitudinally extensive hyperintense signal abnormality on T2weighted FLAIR sequences throughout the central cord (Figure 4-3A). The edema reaches the conus in the majority of cases.20 The cord often appears enlarged in severe cases, but may be already atrophic in untreated patients with advanced disease. The hyperintensity may be bordered by a hypointense rim, which probably represents deoxygenated hemoglobin in the dilated capillaries surrounding the edematous portions of the cord.22 Dilated and tortuous perimedullary vessels belonging to the fistula are seen as flow voids, usually located dorsal to the cord. Heavily T2-weighted sequences, such as three-dimensional phase-cycled fast imaging employing steady state acquisition (PC-FIESTA) and three-dimensional constructive interference steady state (CISS), are more sensitive to the detection of these vascular structures (Figure 4-3B) and are more specific by being less susceptible to pulsation artifacts that may simulate flow voids on a regular T2-weighted sequence.23 Diffuse cord enhancement after contrast administration is not uncommon (Figure 4-3C).22 If cord T2 hyperintensity and perimedullary flow voids are both absent, the chances of a spinal dural arteriovenous fistula are negligible.24 Thus, MRI with optimal sequences can be reliably used to exclude a spinal dural arteriovenous fistula.25 Contrast-enhanced MRA can be extremely helpful to focus the search for the fistula with catheter spinal angiography.26 This technique can demonstrate the early venous filling at the level of the

KEY POINTS

h Leg weakness, leg paresthesia and multimodal sensory loss, back and leg pain, gait impairment, and later sphincter dysfunction are the principal clinical manifestations of spinal dural arteriovenous fistulas. Exacerbation of weakness and pain with activity is also characteristic of the condition.

h MRI of the whole spine should be obtained when a spinal dural arteriovenous fistula is suspected.

h Absence of T2 hyperintensity in the cord and absence of abnormal perimedullary flow voids on MRI can reliably exclude a spinal dural arteriovenous fistula.

h Contrast-enhanced magnetic resonance angiogram of the spine can be very useful in identifying the level of the spinal dural arteriovenous fistula.

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shunt, and this localizing information can be used to guide superselective injections to the most likely arterial feeders, thus reducing contrast and radiation exposure. Selective digital subtraction angiography is nonetheless indispensable to confirm the presence of the fistula and to precisely define its vascular anatomy, including detailed identification of the feeding arteries and draining vein (Figure 4-3D). Treatment planning hinges on this information provided by selected catheter angiography. Differential Diagnosis Because spinal dural arteriovenous fistulas are relatively rare and early symptoms are nonspecific, initial misdiagnosis is a common problem. Incorrect diagnoses made in patients with a spinal dural arteriovenous fistula include spinal stenosis, peripheral neuropathy, radiculopathy, demyelinating disease, spinal cord tethering, and spinal cord tumor. More rarely, conditions such as Guillain-Barre ´ syndrome, ALS, or peripheral vascular disease are incorrectly diagnosed.21 (Case 4-2) Diagnosis is delayed by an average of 11 to 24 months after symptom onset.16,20,27 The importance of considering the diagnosis of spinal dural arteriovenous fistula is highlighted by the results of a study which showed that 22 of 78 (28%) patients who underwent spinal angiography for unexplained myelopathy had a spinal cord AVM, while 19 of the 22 had a spinal dural arteriovenous fistula.28

MRI showing a case of spinal dural arteriovenous fistula. A, T2-weighted fast spin echo sequence, sagittal view, arrow indicating the hyperintense signal caused by the cord edema. B, Fast imaging employing steady state acquisition (FIESTA) sequence, sagittal view, arrow signaling the abnormal vessels dorsal to the cord. C, T1-weighted postgadolinium injection, axial view, arrow pointing to the diffuse enhancement of the cord. D, superselective catheter angiogram confirming the presence of the fistula.

FIGURE 4-3

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Treatment Treatment of spinal dural arteriovenous fistulas consists of permanently eliminating the flow into the arterialized draining vein,17 which can be effectively achieved by surgical disconnection or endovascular occlusion. Surgical treatment of the fistula is performed by a targeted laminectomy, opening of the dura, and

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direct disconnection of the draining vein (Figure 4-429). Surgery is durable and safe; successful resolution of the fistula can be achieved in up to 98% of cases with very low morbidity in experienced hands.30 More recently, endovascular treatment has emerged as a valid alternative for the treatment of spinal dural arteriovenous fistulas.31 Liquid embolic material is injected into a feeding artery to occlude the fistula and the proximal part of the draining vein. The advantages of endovascular therapy include the possibility of pursuing treatment at the time of the diagnostic angiogram, minimal invasiveness, and faster recovery. However, not all fistulas are amenable to endovascular intervention.32 Arterial feeders may be too small to allow safe superselective catheterization for embolization, or a common segmental artery may supply the fistula as well as the spinal arteries, and, in these cases, migration of embolic material may compromise cord perfusion. Rates of recanalization

after endovascular therapy are higher than after surgical treatment.31,33 Thus, patients treated with embolization should be monitored clinically and reexamined with MRI and MRA if symptoms recrudesce. Outcome and Prognostic Factors The vast majority of patients experience either stabilization or improvement of symptoms after treatment of the spinal dural arteriovenous fistula.21,27,34 For most, the benefit is sustained, although a few patients may experience late functional deterioration.35 Motor deficits respond best to the occlusion of the fistula,16,34 and patients commonly report improvements in leg strength that translate into better ambulation within days of the intervention. Conversely, sphincter problems frequently stabilize but less commonly improve after spinal dural arteriovenous fistula treatment.34 Pain, paresthesia, and sensory loss respond variably to obliteration of the fistula, but the intervention typically halts progression of sensory symptoms.

KEY POINTS

h Surgical disconnection of the draining vein represents the definitive treatment of spinal dural arteriovenous fistulas. Endovascular embolization to occlude the draining vein is a valid alternative in selected cases.

h Most patients experience stabilization or improvement of symptoms after treatment of the spinal dural arteriovenous fistula. However, early or delayed worsening can be seen in a small minority of patients, with or without persistence or recurrence of the fistula.

Case 4-2 A 62-year-old man presented to the neurology clinic with a 1-year history of progressive bilateral leg weakness, paresthesia in both legs, and back pain. When walking, the symptoms worsened and the pain radiated to both legs. More recently, he developed erectile dysfunction. He had been given the diagnoses of spinal stenosis and peripheral neuropathy, but wanted a second opinion. On examination, he had asymmetric, bilateral leg weakness and hypoesthesia to all sensory modalities in both legs. His gait was abnormal because of the weakness and proprioceptive loss in the legs. Reflexes were increased in both knees, and he had bilateral Babinski signs. No pinprick level could be defined on sensory examination. A whole spine MRI demonstrated cord edema (extending from the midthoracic level to the conus) and probable tortuous vessels dorsal to the cord. Contrast-enhanced magnetic resonance angiography (MRA) of the spine suggested a spinal dural arteriovenous fistula at the lower thoracic level, which was subsequently confirmed by superselective catheter angiography. He underwent successful endovascular treatment of the fistula with frank improvement of all his symptoms, albeit without full resolution. Comment. The diagnosis of spinal dural arteriovenous fistulas is often delayed by the nonspecific nature of its symptoms. However, a spinal dural arteriovenous fistula should be suspected in a middle-aged man with progressive myelopathy, particularly if the symptoms worsen with exertion. Good-quality MRI using adequate sequences can clearly demonstrate the cord edema and even suggest the presence of the abnormal vessels. When a spinal dural arteriovenous fistula is suspected, contrast-enhanced MRA should be added as it can facilitate localization of the fistula and reduce the work and the risks during spinal catheter angiography. Effective treatment can be delivered by surgery or endovascular embolization. If the fistula is embolized, patients should be followed to exclude delayed recanalization. Continuum (Minneap Minn) 2015;21(1):67–83

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Artist depiction and intraoperative photographs of a spinal dural arteriovenous fistula before and after surgical treatment. Panels A and D show the anatomy of the fistula. The fistula is located within the leaflets of the dura matter of a nerve root sleeve and is formed by the abnormal connection between a radicular artery (1) and a radiculomedullary vein (2), which is a tributary of the coronal venous plexus. The draining vein has become dilated and tortuous due to its direct exposure to arterial pressure. The nerve root (3) is seen exiting the intervertebral foramen. Panels B and E show the exposure of the draining vein before disconnection. Panels C and F display the collapse and blue discoloration of the arterialized venous plexus following surgical disconnection.

FIGURE 4-4

Reprinted with permission from Borlotti C, et al, Contemp Neurosurg.29 B 2014 Lippincott Williams & Wilkins. journals.lww.com/ contempneurosurg/Citation/2014/02150/Spinal_Dural_Arteriovenous_Fistulae.1.aspx.

KEY POINT

h Severity of preoperative deficits is the strongest predictor of outcome after treatment of the spinal dural arteriovenous fistula. However, even patients with severe preoperative disability can benefit from the intervention.

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The degree of preoperative disability is the strongest predictor of outcome after disconnection of the fistula.34 Yet, clinical improvement with treatment of the spinal dural arteriovenous fistula is possible even in patients with longstanding myelopathy.34 Thus, treatment is recommended even when the diagnosis is delayed and the patient presents with severe and prolonged symptoms. Presence of exertional claudication and absence of pinprick level on preoperative physical examination portend better outcome after surgery.34 Meanwhile, neither preoperative MRI

findings nor postoperative changes in the degree of cord edema on MRI predict postoperative outcomes34,36 INTRAMEDULLARY ARTERIOVENOUS MALFORMATIONS Intramedullary (or glomus) AVMs constitute most of the remaining 30% of spinal arteriovenous communications. The nidus of the malformation is located within the parenchyma of the cord and is supplied by branches of the anterior and posterior spinal arteries. Because they are high-flow shunts,

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intranidal and feeding artery aneurysms are seen in more than 40% of cases.37 These vascular anomalies are typically located in the thoracic or lumbar regions. Intramedullary AVMs have no sex predilection and affect children and younger adults, with peak presentation in the third and fourth decades.36 The most common presenting manifestation is hemorrhage, either intramedullary or subarachnoid, which causes back and radicular pain and may produce symptoms of acute myelopathy. Less frequently, more gradual neurologic symptoms can result from mechanical compression, ischemia from vascular steal, or venous congestion. However, venous hypertension is less common than in spinal dural arteriovenous fistulas. Consequently, symptoms are not typically exacerbated by physical activity, and the MRI does not show extensive edema below the level of the lesion. Diagnosis can be made by MRI showing intramedullary flow voids from the dilated vessels.38 MRI can also demonstrate hemorrhage (or cavitation after previous bleeding) and local swelling (or atrophy in chronic cases). Spinal catheter angiography can confirm the existence of the AVM, define its anatomical features, and guide treatment.38 Presence of aneurysm is associated with increased risk of bleeding.39 Treatment of intramedullary AVMs is more challenging than the treatment of spinal dural arteriovenous fistulas because the feeding arteries also consistently supply the cord itself. Therefore, occlusion of the feeding arteries can provoke severe spinal cord ischemia. Staged endovascular embolization with liquid embolic agents, followed by surgery, represents the strategy of choice for most cases.38 CAVERNOUS ANGIOMA Cavernous angiomas in the spinal cord are very rare and much less frequent than in the cerebral hemispheres. Mean Continuum (Minneap Minn) 2015;21(1):67–83

age at onset of symptoms is 42 years, and there is no sex predilection.40Y42 Familial cases account for close to 10% of cavernous angioma cases. Coexistent cerebral lesions are seen in approximately 27% to 42% of cases of spinal cavernous angioma, and this combination is more common in familial cases.40 Rarely, cavernous angiomas can also be seen in the epidural space and cause symptoms by extrinsic spinal cord compression. Spinal radiation at an early age may predispose the patient to the development of intramedullary cavernous angioma years after the exposure, although this association is only supported by case reports and the better-established relationship between cranial radiation and cerebral cavernous angioma risk.43,44 Symptoms may occur because of overt intramedullary hemorrhage (hematomyelia) or growth of the lesion by microbleeding causing compression of adjacent tracts. Consequently, patients present with acute or progressive myelopathy.42 Most lesions are located in the thoracic cord, followed by the cervical cord.41,42 The majority of patients have motor and sensory symptoms below the level of the lesion, more than a quarter present with pain, and a lower percentage present with sphincter dysfunction. The diagnosis can be reliably established by visualization of the lesion on spinal MRI. The cavernous angioma is seen as a lobular mass with heterogenous signal intensity on T1- and T2-weighted sequences, giving the characteristic popcorn appearance.45 The lesion is surrounded by a hypointense rim resulting from the deposition of hemosiderin. Thus, hemosiderin-sensitive sequences, such as gradient echo and susceptibility-weighted imaging, are particularly sensitive for the diagnosis of cavernous angiomas (Figure 4-5).45 Calcifications are less frequent than in cerebral cavernous angioma. There is typically little or no perilesional edema unless a recent

KEY POINTS

h Intramedullary arteriovenous malformations present most commonly with hemorrhage, either within the cord or in the subarachnoid space.

h Treatment of intramedullary arteriovenous malformations is more challenging than the treatment of dural fistulas and usually requires the combination of endovascular embolization and open surgical excision.

h Cavernous angiomas of the spinal cord are rare vascular anomalies that may coexist with cerebral lesions and present with hematomyelia or compressive symptoms as the lesion grows because of microhemorrhages.

h MRI can establish the diagnosis of spinal cavernous angioma. However, cavernous angiomas cannot be visualized on any form of angiography.

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FIGURE 4-5

MRI of a patient with spinal cavernous angioma. Gradient recall echo sequence, axial view, arrow indicating the blooming effect from hemosiderin deposition in the area of the angioma.

KEY POINTS

h It is reasonable to observe spinal cavernous angiomas producing only mild symptoms, but patients with progressive symptoms or recurrent hemorrhages require surgery.

h The main purpose of surgery for spinal cavernous angiomas is to avoid disabling recurrent hemorrhages and progression of neurologic worsening, not to improve existing deficits.

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hemorrhage has occurred. Contrast enhancement is usually minimal or absent, and cavernous angiomas are angiographically occult (ie, not visualized on catheter angiography). The differential diagnosis includes other intramedullary lesions, such as tumors (eg, ependymomas, astrocytomas, metastases, and especially hemangioblastomas), AVMs, demyelination, and transverse myelitis. MRI is usually sufficient to clarify the diagnosis, but noninvasive or catheter angiography may occasionally be necessary to exclude an AVM or hemangioblastoma. Hemorrhagic episodes can lead to stepwise deterioration. A systematic review of available studies suggests that the annual hemorrhage rate is 2.5% (range 0% to 4.5%).42 The natural history of spinal cavernous angiomas is not well known because many patients with progressive symptoms or recurrent hemorrhages are treated with surgery. Yet, patients without severe symptoms who are managed conservatively appear to have a benign

prognosis.46,47 Therefore, incidental or minimally symptomatic lesions should be observed. Definite treatment of spinal cavernous angiomas is achieved by complete surgical resection. Exophytic lesions, particularly if located posteriorly, are most amenable to full excision.41,42 Surgical risk is higher in ventral or deep lesions not abutting the pial surface; those patients should only be operated on if they experience frank progression of deficits or recurrent symptomatic bleeding.42,47 It is important to realize that the purpose of surgery is to avoid disabling recurrent hemorrhages and progression of neurologic worsening, not to improve existing deficits. After surgery, improvement is possible, but many patients remain unchanged and approximately 10% can worsen.41,42,47 VASCULITIS Spinal cord involvement from systemic vasculitis or primary vasculitis of the CNS is exceptionally rare. Infectious vasculitis of the spinal cord can occur with syphilis, and a vasculitic component can be seen with varicella-zoster virus myelitis. The few reported cases attributed to systemic vasculitis (eg, polyarteritis nodosa) have presented with spinal subarachnoid hemorrhage. Epidural hematoma is also possible, and intercostal arteritis can be noted on angiography.48 Clinical manifestations include acute myelopathy and severe back pain. Reported cases of primary CNS vasculitis involving the spinal cord presented with progressive myelopathy and had coexistent cerebral symptoms.49 EPIDURAL HEMATOMAS Epidural hematomas can compress the spinal cord and produce a disabling myelopathy if not evacuated promptly. This complication should be suspected in patients with new cord deficits after spine surgery or epidural catheterization. Main risk factors include advanced age,

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multilevel surgery, and anticoagulation, especially in the perioperative period.50 Spontaneous spinal epidural hematomas (cases without identified cause) are infrequent but not exceptional.51 Presenting symptoms depend on the location of the hematoma and degree of compression. More commonly, epidural hematomas manifest with sudden local pain in the neck or the back and sometimes with radicular radiation, associated with motor and sensory deficits that progress over hours.50 When severe, the presentation of epidural hematomas may simulate spinal cord infarction. Diagnosis of an epidural hematoma is confirmed by imaging, and, while CT scan may be diagnostic in most cases, MRI provides more definite information on the extent of the hematoma and the degree of cord compression. The typical imaging appearance of an acute spinal epidural hematoma is a mass with hyperintense to isointense signal on T1-weighted and hyperintense signal on T2-weighted sequences and without gadolinium enhancement (unlike the enhancement seen with epidural abscesses).52 Some hematomas can have heterogeneous signal, especially in the setting of anticoagulation. Treatment consists of emergency surgical evacuation when patients have myelopathic symptoms. Long hematomas, impaired perioperative hemostasis, and complete motor and sensory loss before surgery (American Spinal Injury Association [ASIA] grade A) predict a worse prognosis.53 Patients who only have pain may be managed conservatively, but must be monitored carefully for the development of compressive symptoms.

Although relatively uncommon, vascular disorders should be considered in the differential diagnosis of both acute and progressive myelopathies. MRI (combined with MRA when appropriate) using contemporary sequences can be diagnostic in many cases when interpreted by trained specialists. Catheter angiography is necessary to confirm the presence of spinal dural arteriovenous fistulas and intramedullary arteriovenous malformations. Vascular anomalies affecting the spinal cord are treatable, and therapeutic plans should be decided in close collaboration with a vascular neurosurgeon.

CONCLUSION Diagnosis of vascular myelopathies demands knowledge of the most distinctive clinical and radiologic characterstics of these diseases and knowledge of the vascular anatomy of the spinal cord.

8. Nedeltchev K, Loher TJ, Stepper F, et al. Long-term outcome of acute spinal cord ischemia syndrome. Stroke 2004;35(2):560Y565. doi:10.1161/01.STR.0000111598.78198.EC.

Continuum (Minneap Minn) 2015;21(1):67–83

KEY POINT

h Spinal epidural hematoma may be a serious complication of spine surgery or epidural catheterization, especially in coagulopathic patients, and emergency evacuation is mandatory in patients with symptoms and signs of myelopathy.

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Vascular myelopathies.

Vascular myelopathies include several diagnoses that are often misdiagnosed or undertreated. Some represent neurologic emergencies, such as spinal cor...
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