SPINAL ARTERIOVENOUS MALFORMATION (Angiomatous malformation)
Arterio-venous malformations (AVMs) are congenital abnormalities of blood vessels rather than neoplastic growths. Arteries communicating directly with veins bypass the capillary network which has failed to develop, creating a 'shunt'. The AVM appears as a mass of convoluted dilated vessels.
Cervical: uncommon site (~ 15%)
Arises from the anterior spinal artery and usually lies within the cord substance (intramedullary). ----
Upper thoracic: (20%)
Thoracolumbar: this is the commonest site (~65%). It may be extra- or intradural^ or within both compartments. The main feeding vessels are often dural arteries of the spinal nerve roots (Dural fistula). Intramedullary lesions at this site arc less common.
Spinal AVMs may present clinically at any age in either sex, but dural lesions are most common in males between 40-70 yrs of age.
Clinical features sudden onset (10-15%)
Due to - subarachnoid haemorrhage: headache, neck stiffness, back and leg pain
— extradural haematoma
— subdural haematoma \ signs of acute cord damage.
— intramedullary haematoma (haematomyelia)
gradual onset (85-90%) Probably due to | venous pressure but other factors may play a part:
- venous thrombosis
- 'steal' phenomenon
- venous bulk
- arachnoiditis (if previous bleed).
Progressive deterioration of all spinal modalities simulating cord compression. Pain is common. With thoracolumbar lesions a mixed u.m.n./l.m.n. weakness in the legs is typical.
Intramedullary AVMs may cause fluctuating signs and symptoms and may mimic intermittent claudication.
A bruit may be heard overlying a spinal AVM and occasionally midline cutaneous lesions - haemangiomas, naevi or angiolipomas - are found. (Note that cutaneous angiomas are not uncommon and do not necessarily imply an underlying lesion.)
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