Arteriovenous Malformations/Fistulas of the Cervical Spinal Cord
October 16th, 2009 by Administrator

The author: Professor Yasser Metwally


October 16, 2009 — The nomenclature of spinal vascular lesions has evolved with better understanding of lesional angioarchitecture. For our discussion, the classification system proposed by Anson and Spetzler[8] will be used as follows: type I– dural arteriovenous fistulas (DAVFs), type II and III–intramedullary arteriovenous malformations (AVMs), and type IV–intradural/extramedullary (perimedullary) spinal AVMs. Since a discussion of all four types of vascular abnormalities would be beyond the scope of this text, only type I lesions will be discussed in the context of the cervical spine.

The most common lesions are type I lesions, which comprise up to 80% of all spinal AVMs, and are thought to be secondary and acquired. They are 4 times more common in men, usually between 40 and 70 years of age, and are often found in the lower thoracic or upper lumbar region. The angioarchitecture of these lesions is composed of a radicular artery branch that communicates with an intradural medullary vein via a fistula at the dural root sleeve. This medullary vein then drains cephalad into serpiginous dilated pial veins of the spinal cord. This results in chronic arterialization of veins, leading to elevated pressures and venous engorgement that produce changes in spinal cord parenchyma. Ultimately, there is a decrease in tissue perfusion and a resultant hypoxia due to transmission of these elevated venous pressures to intrinsic spinal cord veins.[9,10]

With time, this progressive spinal venous hypertension manifests clinically as a distinctive chronic myelopathy with progressive weakness and sensory deficits.[9,11] The most common symptom is progressive lower extremity weakness without upper extremity involvement. Other manifestations also include back pain, sensory deficits, and bowel and bladder dysfunction. Delayed diagnosis is not uncommon, as there is usually a slow progression of symptoms over a 2- to 3-year period.[9] The so-called Foix-Alajouanine syndrome or subacute necrotic myelopathy, an eponym associated with type I lesions, is the result of chronic venous ischemia that could potentially lead to cord infarction.[9,10]

Radiographically, prone myelography demonstrates tortuous vessels and cauda equina beading. It is a sensitive test, though not as specific as MRI, which can show cord enlargement, central cord T2 prolongation, dorsal serpentine flow voids (more specific), and dilated vein enhancement[9-11] (Figure 1). Ill-defined and patchy enhancement of the affected portion of the spinal cord is not uncommon. Nevertheless, catheter-based spinal angiography remains the gold standard for the diagnosis of spinal AVM.[9]

Figure 1. Dural arterial venous fistula. (A) Sagittal T2-weighted image with diffuse intramedullary T2 signal abnormality extending from the conus cranially (arrows). (B) Postgadolinium sagittal T1- weighted images show numerous enhancing veins posterior to the conus (arrows) to the cervical region. (C) First-pass gadolinium-enhanced MR spinal angiogram shows tortuous dilated veins with the spinal canal (arrows). (Click to enlarge figure)

Figure 1. Dural arterial venous fistula. (A) Sagittal T2-weighted image with diffuse intramedullary T2 signal abnormality extending from the conus cranially (arrows). (B) Postgadolinium sagittal T1- weighted images show numerous enhancing veins posterior to the conus (arrows) to the cervical region. (C) First-pass gadolinium-enhanced MR spinal angiogram shows tortuous dilated veins with the spinal canal (arrows). (Click to enlarge figure)

For the cervical spine, type I lesions are rare,[12-15] and cervical DAVFs can manifest as a progressive myelopathy, similar to those in the thoracolumbar spine. Interestingly, unlike those in the thoracolumbar region, cervical DAVFs present more often with hemorrhage, such as subarachnoid hemorrhage (SAH) at the craniocervical junction.[12,16] The angioarchitecture of cervical DAVF can take one of three forms. First, as in the thoracolumbar spine, the feeding radicular artery may drain into a medullary vein along the length of the cervical spinal cord, usually dorsally, and present with myelopathy[10,13] (Figure 2). Interestingly, the signal abnormality from a cervical DAVF tends not to involve the medulla.[17]

Another pattern is that the DAVFs can decompress entirely into the intracranial venous system and thus decrease venous hypertension in the cervical cord. These patients may not present with myelopathy but with SAH because of intracranial venous enlargement. Alternatively, patients who drain caudally into a medullary vein would be more likely to present with myelopathy than with SAH.[16]

The third scenario involves an intracranial DAVF that produces cervical myelopathy. An intracranial DAVF can drain into spinal veins and produce symptoms secondary to venous hypertension, similar to DAVFs in the thoracolumbar spine.[10] These lesions can manifest as intracranial hemorrhage, ischemia/infarction, mass effect from enlarged veins, increased intracranial pressure, and cranial neuropathies. T2 prolongation within the cervical cord and medulla, cord enlargement, and flow voids dorsal and ventral to the cervical cord are typical MRI findings.[17]

The initial method of treatment of symptomatic type I DAVFs is primarily endovascular with successful >80% of cases. Permanent liquid agents, such as N-butylcyanoacrylate, are preferred as particulate embolic material results in almost 100% recanalization. If endovascular treatment is unsuccessful or contraindicated, surgical removal of the nidus is usually a safe alternative.[9]


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