Diagnosis: Spinalduralarteriovenousfistula (SDAVF)
Discussion: Spinal dural arteriovenous fistulas are underdiagnosed despite being the most common spinal vascular malformation accounting for about 70% of all spinal vascular malformations. A major German referral center for spinal vascular disease arrived at 5-10 million cases per year in the general population. The exact etiology is unknown. A strong male predominance is noted with males being affected five times more often than women. Mean age at diagnosis of 55 to 60 years.
Most fistulas are in the thoracolumbar region (most commonly between T6-L2) and solitary. SDAVFs are supplied by radiculomeningeal arteries. The AV shunt is located inside the dura mater near the nerve root. Increased pressure within the venous system because of arterialization leads to venous congestion causing chronic hypoxia and progressive myelopathy.
SDAVFs are organized into three groups based on the embryologic development of their venous drainage: ventral, dorsal and lateral epidural (which is the most common type). The shunts develop in the lateral epidural space at the junction of the radicular veins to the epidural venous system and due to outflow obstruction blood flow is shunted into the perimedullary veins.
Initial clinical symptomatology vary and could include gait disturbace and sensory symptoms such as paresthesias, sensory loss and also lower extremity radicular pain. Classically, neurologic symptoms progress and can often be ascending. In the more latter stages of the disease, bladder and bowel incontinence, erectile dysfunction and urinary retention can be seen. Upper motor neuron disease showing clonus and positive Babinski sign can be seen.
Diagnosis can be aided by MRI and MRA with confirmation with DSA. MRI findings of spinal cord edema plus dilated perimedullary vessels without an intramedullary lesion are typical for an SDAVF. On T2WI, ill-defined centromedullary cord edema is seen at multiple levels. Dilated perimedullary capillary vessels can be seen in these regions. If the shunt volume is small, the perimedullary vessels may only be seen after contrast enhancement. Cord enhancement can be seen due to blood-spinal cord barrier breakdown with chronic venous congestion. As the disease progresses, the spinal cord can atrophy.
First-pass enhanced MRA can show venous filling and confirm the shunt and may be able to better define the level of the shunt and in effect decrease the radiation dose the patient will need for subsequent traditional angiography. Traditional selective angiography can show stasis of contrast within the radiculomedullary arteries with delayed venous return suggesting congestion. Normal venous return after injection of the anterior spinal artery can exclude the possibility of a SDAVF.
Treatment is centered around occluding the most distal arterial supply with the most proximal draining vein. Options include surgical occlusion or endovascular treatment. The primary goal is to halt the progression of pathology. Only about 67% of patients have regression of motor symptoms with only about 33% having improvement in sensory disturbances. Impotence and sphincter disturbance rarely resolve. Deterioration of symptoms after initial improvement should suggest recanalization of shunt or development of another shunt.
In any male patient of middle age with ascending sensory or motor lower extremity deficit, SDAVF should be among the differential considerations to prevent irreversible damage.
