Overview of spinal dural arteriovenous malformation
Spinal dural arteriovenous malformations account for 15% to 20% of spinal arteriovenous malformations, and are more common in males, with a male-to-female ratio of 4 to 8:1. The age of onset of this disease is around 45 years old, and the lesions preferentially occur in the thoracolumbar region, with no obvious tendency of family morbidity. Statistics show that patients with this type of disease are often accompanied by acquired diseases, which may be related to traumatic factors, but the exact mechanism is not clear.
Etiology
In dural arteriovenous malformations, the arterial supply originates from the dural branches of the spinal segmental arteries. In most cases, the arteriovenous short circuit occurs within the neural foramen on the dorsal lateral aspect of the neurogenic cuff, where arterial blood is injected into the draining vein, resulting in increased pressure and tortuous dilatation, which interferes with the return of blood to the spinal cord and causes ischemia and degeneration of the spinal cord. The segmental arteries in the plane of the arteriovenous fistula supply either the anterior or posterior spinal artery. The lesion usually has only one trophoblastic artery, which is type IA. When the lesion is supplied by 2 or more vessels, it is characterized as type IB.
Symptoms
1. Pain
Pain is the most common symptom in patients with spinal arteriovenous malformation. Pain in the back or buttocks of the thoracolumbar segment may be the main symptom, and radicular pain may also occur. Its incidence accounts for 40% to 50% of the cases in this group.
2. Movement disorder
In patients with spinal dural arteriovenous malformation. 30% to 40% are associated with motor dysfunction, which is usually a mixed dysfunction of upper motor neurons and lower motor neurons associated with the lumbosacral spinal cord. Clinical examination reveals signs of atrophy of the gluteal and gastrocnemius muscles, often combined with hyperreflexia of the lower extremities. Symptoms may be aggravated by physical labor, prolonged standing and various postures such as stooping, bending, stretching or flexing.
3. Sensory impairment
About 1/3 of the patients may have sensory disorders, which may be characterized by dullness of sensation, skin sensitization or other abnormalities, or absence of tactile or positional sensation.
4. Other symptoms
Subarachnoid hemorrhage can also occur in patients with spinal dural arteriovenous malformation, but it is rare. Acute necrotizing myelopathy due to venous thrombosis may also occur and may lead to sudden paralysis (Foix Alajouanine syndrome), possibly due to the sudden reflux of thrombus from the vein.
Tests
1. MRI (magnetic resonance imaging) examination
MRI of the spinal cord shows that the lesion is located in the posterior and lateral part of the spinal cord. In the sagittal position, the lesion is in the shape of a shuttle, the long axis is parallel to the spinal cord, and the dorsal part of the spinal cord shows a band-like high signal shadow, and the spinal cord is in the stage of edema, the range of degeneration is more than 5 segments, and the spinal cord can be seen to be surrounded by the low-signal blood-retention shadow. Enhancement scan: Sagittal view shows bead-like high signal tortuous blood vessels in the posterior aspect of the spinal cord, and coronal view shows tortuous blood vessels located in the posterior aspect of the spinal cord.
2. CTM (myelography plus CT) examination
It tends to be more sensitive and specific for this disease. A large, convoluted vessel can be seen on the dorsolateral aspect of the spinal cord on CTM scanning compared to no contrast. The imaging should be performed with the patient in the supine position to check for venous return within the dura mater. Arteriovenous malformations of the dura mater are rarely seen as complete obstructions on CTM images.
3. Selective spinal arteriography
Selective spinal arteriography is the most ideal diagnostic method to identify this disease. On angiography, the anterior spinal artery is easily recognized, and the blood supply associated with the dural arteriovenous malformation can be identified. All trophoblastic arteries in the lesion area should be identified to prevent recurrence of postoperative arteriovenous fistulae.
Diagnosis
The predominantly progressive development of mixed upper and lower motor neuron paralysis may be combined with pain, sensory deficits, gluteal atrophy, and sphincter dysfunction in middle-aged and older men. Whether the arteriovenous fistula is located above or below the level of the lumbosacral region, most of the symptoms are related to the lumbosacral segment of the spinal cord. Eighty percent of these patients present with slowly developing spinal cord disease, and about 10% have an acute onset. The disease is easily misdiagnosed, with only about 30% of cases being diagnosed within 1 year of onset, and more than half of the other patients being diagnosed 2 to 3 years after the onset of symptoms.
Treatment
1. Endovascular treatment
Where there are indications for surgical treatment, it is generally advocated that endovascular treatment should be carried out first, the main purpose of which is to embolize or occlude the distal trophoblastic artery, arterial and venous traffic branches and the proximal part of the intradural venous reflux. Currently, polyethylene ethanol suspension dissolved in contrast medium is mostly used to inject into the root of the trophoblastic artery for embolization. Alternatively, isobutyl 2-acrylate (ICBA) or non-isobutyl acrylate (NBCA), which is a liquid bolus that can be injected through a small-bore catheter, can be used. After a latent period in the vessel, polyvinylation of the injection and atresia of the vessel occur. The latency period can be controlled by varying the concentration of cyanoacrylate, the amount of contrast agent, and glucose.
2. Surgical treatment
Surgical treatment of spinal dural arteriovenous malformations is mainly accomplished by microsurgical techniques, including electrocoagulation and dissection of the refluxing veins in the dura mater, resection of the arteriovenous malformation in the radicular sleeve of the dura mater, or simultaneous electrocoagulation and dissection of the refluxing veins.
Prognosis
The outcome of the surgery depends on the preoperative neurological status of the patient, and the effective rate can be more than 80%, but there are also cases of deterioration generally within 8%.