Overview of spinal cord vascular malformations
Intramedullary arteriovenous malformations are a type of spinal vascular malformations, which are categorized as type II (globular vascular malformations) and type III (immature or extensive vascular malformations).
Etiology
The arteriovenous mass is located within the spinal cord and has multiple blood-supplying arteries, including the spinal medullary artery, the central sulcus artery, the posterior lateral spinal artery, and multiple draining veins. According to the pathologic pattern of arteriovenous malformations, there are spherical and naive types, the former being spherical with no normal spinal cord tissue inside, and the latter being in the form of a mass with normal spinal cord tissue inside.
Symptoms
The clinical manifestations of patients with intramedullary type are significantly different from those with dural type. The former is common in adolescents and children, and often starts with intramedullary and subarachnoid space hemorrhage. About 3/4 of the patients have a history of hemorrhage, and 1/3 of the patients present with acute neurological dysfunction, which manifests as progressive limb muscle weakness, sensory deficits, sphincter dysfunction and sexual dysfunction. About 1/5 of patients with intramedullary vascular malformations have intramedullary aneurysms, which are often located in the major trophoblastic vessels supplying the medulla, and the majority of patients with spinal aneurysms present with subarachnoid hemorrhage and have a long history of the disease.
Tests
MRI (magnetic resonance imaging) plays an important role. Intramedullary lesions can be differentiated by the presence of flow-void signs on T1-weighted images. Abnormal signals are often seen in the spinal cord on T2-weighted images, and a peri-spinal airflow sign suggests peripheral spinal varicose veins. In the presence of intramedullary hemorrhage, T1W1 and T2W1 high signal is seen. Spinal arteriography plays a more important role in determining the extent and nature of intramedullary lesions, and DSA (digital subtraction angiography) is especially helpful in distinguishing between type II and type III lesions. This should be done selectively, with bilateral brachial or bilateral femoral arterial injection angiography if necessary. As part of the screening tests, selective aortic cannulation as well as cannulation angiography of the vertebral arteries, carotid arteries, and iliofemoral vessels are useful in identifying the trophoblastic arteries supplied by the intramedullary lesion and may be chosen as appropriate.
Diagnosis
In addition to general clinical symptoms, MRI plays an important role in the diagnosis of intramedullary vascular malformations, and intramedullary snipe lesions can be distinguished by the flow-void sign on T1-weighted images. In the T2-weighted image, there are often abnormal signals in the spinal cord, and the airflow sign around the spinal cord suggests the peripheral part of the spinal cord lesion. Spinal arteriography is more important in determining the extent and nature of intramedullary lesions, and the DSA technique, in particular, is helpful in differentiating between type II and type III lesions. The procedure should be performed selectively, and bilateral brachial or bilateral femoral arterial injection angiography may be performed if necessary. Selective aortic cannulation, as well as cannulation of the vertebral arteries, carotid arteries, and iliofemoral vessels as part of the screening test, are useful in identifying the trophoblastic arteries supplied by the intramedullary lesion, and may be chosen as appropriate.
Treatment
Treatment of intramedullary vascular malformations often requires endovascular therapy in conjunction with microsurgery. Endovascular therapy is most effective when branches of the posterior spinal artery are supplied by multiple arteries. Injection angiography of the anterior spinal artery is complicated by the possibility of compromising normal spinal blood flow, especially if the anterior spinal artery does not terminate in a snipe at the vascular malformation, and temporary balloon occlusion, the isoamylbarbital test, and somatosensory evoked potentials can help in the selection of endovascular treatment cases. Polyvinyl alcohol and cyanoacrylates are commonly used for endovascular treatment of such lesions.
Microsurgical treatment is appropriate for intramedullary multiple vascular ballooning lesions, and these cases often have a clear arterial supply. Immature-type lesions are much more extensive within the spinal cord, and it is often difficult to differentially isolate these lesions from functional spinal cord tissue. In general, lesions located in the dorsal or midline region are most amenable to surgical resection, especially if they extend cephalad or caudally, including more than two vertebrae; however, lesions closely connected to the anterior spinal artery are not amenable to surgery.
The neurologic function of patients with untreated intramedullary vascular malformations progressively deteriorates; after 10 to 20 years, there is significant deterioration in neurologic function in about half of the cases. In patients whose lesions can be surgically removed, the outcome is mostly satisfactory and stable. Of those whose intramedullary lesions were completely removed, 60% showed improvement in neurologic function.