Intramedullary AVM

The intramedullary arteriovenous malformation is also known as a type II or classic AVM. Spinal cord AVMs are the second most common spinal vascular malformation. The angioarchitecture of these lesions is similar to that of classic brain AVMs, with multiple arterial feeders, a nidus, and draining veins. The nidus can be compact (glomus type) or diffuse (occasionally called juvenile type, not to be confused with the metameric type). The arterial feeders are usually multiple branches of the ventral spinal axis (ASA) and/or dorsolateral pial network (PSAs). These lesions are high-flow, high-pressure, low-resistance malforma-tions.1 In their new proposed classification, Spetzler et al. subdivided these lesions into those with compact (glomus-type) nidus and those with a diffuse nidus.

The natural history is difficult to ascertain, but the majority of patients present before the age of 40.8 The most common presentation is an acute myelopathy due to intramedullary and/or subarachnoid hemorrhage.1,8 A proportion of patients present with intermittent or progressive myelopathy with deterioration of limb function or bowel and bladder function.

The progressive myelopathy can be due to vascular steal, venous hypertension, or venous compression.1 Pain also is a common presenting symptom in these patients. If left untreated, patients can be expected to experience an episodic but progressive deterioration due to repetitive bleeding.8 In one 8-year study of 60 patients, 36% of patients younger than 41 years of age, and 48% of patients aged 41 to 61 were wheelchair bound within 3 years of diagnosis.13 Based on Djindjian's original series of 150 patients, 13% of patients at the 5-year follow-up, 20% of patients at the 10-year follow-up, and 57% of patients at the 20-year follow-up had experienced clinical deterioration.14a

Therapy

Surgical resection is difficult and bears high morbidity because of the intramedullary location and because blood is supplied from tiny perforators arising from sulcocommissural branches. These may arise as en passage arteries that supply normal cord tissue. A carefully planned, staged embolization with obliteration of the most proximal draining pial vein with NBCA may be curative (Figure 16.3). Frequently, repeated PVA particle embolization may be the only alternative to reduce the size of the AVM nidus and to effect temporary symptomatic relief.1517 If a surgical resection is planned, preoperative particle or NBCA embolization may be helpful.

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