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Recent reviews of both spinal cord infarction and spinal dural arteriovenous malformations have highlighted the importance of vascular disease as a cause of acute or chronic myelopathy.1–3 Spinal cord stroke is generally encountered following aortic surgery, aortic dissection or after periods of prolonged hypotension associated with advanced vascular disease. Fibrocartilage embolism is a rare but important cause of spinal cord infarction, particularly in young people where the consequences can be devastating. Retrograde embolisation of fragments of the nucleus pulposus from the vertebral vasculature to the radiculomedullary arteries is provoked by physical exertion, trauma and Valsalva manoeuvre, and may account for 5% of spinal cord infarction.4
Spinal cord infarction generally affects the anterior spinal territory and causes a sudden flaccid paralysis associated with areflexia, loss of sensation to pain and temperature, and autonomic deficits (atonic bowel/bladder, paralytic ileus and loss of sphincter tone). There is often acute back pain at the onset, usually at the level of the lesion.5 Dorsal column function is generally well preserved although there is considerable variability. Other acute presentations of cord infarction include respiratory failure, posterior spinal artery territory infarction causing loss of proprioception, complete transverse cord infarction with loss of all motor, sensory and autonomic modalities below the lesion, Brown-Séquard syndrome and central cord involvement. Following spinal surgery, urgent spinal imaging is essential to exclude compressive epidural haematoma.
New spinal cord infarction diagnostic criteria emphasise three major components: first, the rapid development of severe deficits within 12 hours; second, MR imaging excluding compression; and third, cerebrospinal fluid (CSF) showing no inflammatory changes. The MR imaging is normal in about a third of patients, but characteristic abnormalities may include T2 hyperintensity ‘owl eyes’, pencil-like hyperintensity and gadolinium enhancement that is often linear located in the anterior grey matter with diffusion weighted/apparent diffusion coefficient restriction.3 6
Treatment involves trying to improve cord perfusion through collateral flow. This entails a combination of haemodynamic augmentation (vasopressor to avoid hypotension) and lumbar drainage (often with CSF removal to augment microvascular flow). The evidence base to support these techniques is limited.7
The prognosis of spinal cord infarction depends on the severity of the deficit at outset, but some patients do achieve a substantial recovery despite extensive involvement. Robertson et al 8 noted 41% of patients eventually regained mobility, Novy et al 5 describe complete or incomplete recovery in 70% of 27 patients and Nedeltchev et al noted that 41% of 54 patients regained full walking ability and 30% could walk with aids.9
This issue of Practical Neurology contains a case study highlighting the importance of considering dural arteriovenous fistula (in this case intracranial) in the differential diagnosis of acute or progressive cervical myelopathy. Spinal dural arteriovenous malformations may be difficult to diagnose, but they are amenable to treatment and a good outcome, with timely recognition. The potentially devastating consequence to the patient’s functional capacity if the diagnosis is missed and appropriate effective treatment is not started is the obvious reason for its delayed diagnosis being a disproportionately frequent cause of medical litigation. A spinal dural arteriovenous malformation is often misdiagnosed as an inflammatory, infective or neoplastic myelopathy because of intraparenchymal gadolinium enhancement.
Spinal dural arteriovenous malformations are characterised by an abnormal direct communication between a radiculomedullary artery and vein without an intervening capillary bed. The vessels become engorged and cannot adequately drain the influx of blood, resulting in venous hypertension and ultimately infarction. The fistula site itself is most commonly at the dural sleeve of the nerve root in the intervertebral foramen.
The difficulty in recognising and diagnosing spinal dural arteriovenous malformations is due to their relative rarity, the non-specific nature of the associated symptoms, particularly in patients who have risk factors for other conditions, and their ability to mimic a range of pathologies leading to misdiagnosis with potentially serious consequences. It is essential to maintain a high index of suspicion for their presence when considering the differential diagnosis of any progressive myelopathy.
The onset is generally insidious with slow progression. The diagnosis can be delayed by an average 11–24 months after symptom onset and there is often a fixed deficit at the time of presentation. Initial symptoms generally involve sensory loss in the legs and weakness, which is often asymmetrical at onset but becomes bilateral and symmetrical over time. Leg weakness and pain often worsens with exertion and prolonged standing, and is relieved by rest and recumbency. Sphincter dysfunction involves both urinary and faecal retention and incontinence, often associated with erectile dysfunction and is commonly present by the time of diagnosis.10 Cervical spinal dural arteriovenous malformations are rare but may present with atypical features including upper limb involvement and respiratory impairment.2
It is exceptional for any patient with progressive myelopathy not to undergo imaging of the spine but the diagnosis is still missed. It is important that clinicians should ask the question, ‘Could this be an arteriovenous fistula?’. Scanning should encompass the entire cord because the physical examination cannot localise the level of the fistula. Cord oedema and ischaemia from the effects of venous hypertension manifest as a longitudinally extensive hyperintensity on FLAIR in the central cord that usually reaches the conus. Hyperintensity may be surrounded by a rim of hypointensity due to deoxygenated haemoglobin in the dilated capillaries. Dilated and tortuous perimedullary vessels belonging to the fistula are seen as flow voids usually located dorsal to the cord on T2-weighted sequences. Contrast-enhanced MR angiography can show early venous filling at the level of the shunt.11 There is a recently described unique gadolinium enhancement pattern in which there is at least one focal geographical non-enhancing area within a long segment of intense holocord gadolinium enhancement termed ‘the missing piece sign ’.12 Newer three-dimensional radiology techniques have facilitated vessel identification.13 Four-dimensional contrast-enhanced MR angiography reduces the time of acquisition without markedly compromising spatial resolution. This is particularly valuable in imaging high-flow vascular malformations in children when conventional imaging may be compromised by faster heart rate, more rapid arteriovenous transit, smaller structure and smaller volume of contrast agent used.14
The differential diagnosis is extremely wide. Ascending paraesthesiae and dysaesthesiae in the legs can be wrongly ascribed to peripheral neuropathy (and in particular to Guillain-Barré syndrome) or radiculopathy. Spinal dural arteriovenous malformation is also commonly misdiagnosed as demyelination, motor neurone disease, spinal stenosis with claudication or as a spinal cord tumour.
The treatment is to eliminate the flow permanently into the arterialised draining vein. This can be done either by surgical disconnection or endovascular occlusion. Surgery involves a targeted laminectomy, opening the dura and directly disconnecting the draining vein. This is a durable, safe procedure and is said to be successful in 98%.15 Endovascular treatment involves injecting liquid embolic material into the feeding artery to occlude the fistula and the proximal part of the draining vein. The advantages of this procedure are that it is possible to pursue treatment at the same time as diagnostic angiography, the procedure is minimally invasive and recovery is faster. Not all fistulas are amenable to endovascular intervention, either because the arterial feeders are too small to allow super-selective catheterisation for embolisation or because a common segmental artery may supply the fistula and the spinal arteries. Furthermore, the rates of recanalisation after endovascular treatment are higher than after surgery.16
The vast majority of patients experience either stabilisation or improvement in symptoms after treatment of the spinal dural arteriovenous malformation, but early intervention is important to prevent progression.17 Following successful occlusion, progression can be halted in most cases18; however, only two-thirds have regression of motor symptoms and one-third show improvement in sensory disturbance.19 Sphincter and sexual disturbance are rarely reversed and pain may persist. In the largest series, Muralidharan et al 20 noted that preoperative exertional claudication and the absence of a pinprick level correlated with a greater chance of postoperative improvement. In their series, 44% of patients improved and 34% stabilised after surgical intervention; some patients significantly improved after surgery despite severe preoperative impairment. Nonetheless, it is clear that the early recognition of spinal dural arteriovenous fistulas is critical to achieving the best postoperative outcome.
Funding The author has not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Commissioned. Externally peer reviewed by David Werring, London, UK.
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