Overview
This is an intradural peri-spinal arteriovenous fistula with an intradural arteriovenous fistula supplied directly by the anterior spinal artery. The arteriovenous fistula and its reflux vein are located outside the spinal cord, and the lesion has not spread into the spinal cord. This type is subdivided into three subtypes: IVA, IVB, and IVC. These lesions consist of a direct anastomosis between the intramedullary artery (or occasionally the posterior spinal artery) and the intradural refluxing vein, and are often located at the thoracolumbar junction.
Etiology
The etiology is unknown.
Symptoms
1. Clinical features
Most patients with this type are young. Symptoms often appear before the age of 40, and its incidence accounts for about 1/6 of all cases, half of which are type IVA patients. Most patients present with progressive myelopathy, accompanied by pain, weakness, and sensory and sphincter dysfunction, or subarachnoid hemorrhage.
The functional involvement of the spinal cord in these patients is similar to that of those with type I spinal vascular malformations. Vascular congestion is due to elevated intradural venous pressure. Type IVC affects the function of the spinal cord and nerve roots because the lesion is so extensive that it causes compression. Some of these patients may be acquired.
2. Types
(1) Type IVA is characterized by a single trophoblastic artery or a relatively slow-flowing, moderately thick intradural vein.
(2) Type IVB is characterized by the presence of multiple trophoblastic arteries with large refluxing veins and increased blood flow.
(3) Type IVC The lesion is more extensive and often has multiple trophoblastic arteries which return into dilated intradural veins.
Examination
Selective angiography may show the distribution of the anterior spinal artery to the arteriovenous fistula and the returning veins. Sometimes it shows large perispinal flow-void signs, mainly in the form of markedly dilated intradural venous reflux, and these malformations are often seen near the cones of the thoracolumbar junction and proximal to the cauda equina.
Diagnosis
Diagnosis is difficult because the disease has no specific clinical features. Unexplained progressive spinal cord damage with intermittent seizures associated with activity should raise a high level of suspicion for this disease. The coexistence of spinal and neurogenic dysfunction with sudden onset and recurrent seizures helps in the diagnosis of the disease. The location of the malformed vessels can be detected by MRI, and further spinal angiography can clarify the diagnosis.
Complications
Most patients have progressive myelopathy as a complication.
Treatment
This type of spinal vascular malformation can be treated with endovascular therapy or microsurgery, or a combination of both.
1. Types IVA and IVB
Type IVA is usually not suitable for endovascular treatment due to the small size of the lesion, thin trophoblastic arteries and low blood flow. Surgery, including intraoperative angiography to identify the arteriovenous fistula and block it, is the most effective treatment for type IVA and IVB lesions, especially for lesions on the lateral side of the thoracolumbar spinal canal.
2. Type IVC
For type IVC lesions, a floating balloon can be used, or metal coils or injectable embolic substances can be used for endovascular embolization.