Spinal arteriovenous fistulas (spinal AVFs) are characterized by abnormal communication and shunting of blood from an artery to a vein of the spine that bypasses the capillary bed.
They are classified by size and angioarchitecture and are distinct from spinal arteriovenous malformations, which collectively are known as spinal vascular malformations 7:
According to the Takai classification of spinal arteriovenous shunts, they are divided into:
spinal dural arteriovenous fistula (type I)
spinal perimedullary arteriovenous fistula (type IV) - rare
spinal extradural arteriovenous fistula (type V) - rare
These are discussed in more detail separately.
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Epidemiology
Spinal arteriovenous fistulas represent approximately 70% of all spinal vascular malformations 1,2.
Clinical presentation
Clinical presentation depends on the type and size of the lesions.
Most commonly, they cause spinal venous congestion, the symptoms of which are nonspecific and include 3,4:
motor symptoms such as gait disturbance and reduced power
sensory symptoms such as paresthesia
radicular pain
The symptoms can be intermittent, progressive and ascending and relate to cord edema as opposed to the exact location of the arteriovenous fistula 4.
Late symptoms include 5:
bowel and bladder incontinence
erectile dysfunction
Additionally, larger lesions can present with compressive symptoms, including 9:
radiculopathy
myelopathy
Pathology
The pathogenesis of arteriovenous fistulas is unknown and hypothesized to be an acquired condition 6.
Radiographic features
MRI
Classic findings include 6:
tortuous and enlarged vessel flow voids around the spinal cord
spinal cord edema that is usually centromedullary and multisegmental
A low T2 rim at the periphery of the edema is thought to be secondary to deoxygenated blood product 8.
DSA
DSA is the gold standard modality for imaging of arteriovenous fistulas. It allows confirmation of diagnosis with precise identification and mapping of the arterial feeding and venous drainage of the fistulas. The exact angiographic features will vary depending on the type of lesion.
Treatment and prognosis
General treatment aims to occlude or obliterate the shunting zone from both the arterial and venous part of the arteriovenous fistula. Microsurgical and/or endovascular strategies have a role depending on local expertise and the type of the lesion 7.