INVESTIGATIONS (contd) Angiography
Four-vessel angiography confirms the presence of an AVM and delineates the feeding and draining vessels. Occasionally small AVMs are difficult to detect and only early venous filling may draw attention to their presence. n.b. In the presence of a haematoma, angiography should be delayed until the haematoma resolves, otherwise local pressure may mask demonstration of an AVM. If the angiogram is subsequently negative, then MRI is required to exclude the presence of a cavernous malformation.
Various methods of treating arteriovenous malformations are available, but all risk further damage. The urgency of the patient's clinical condition and the risks of treatment must be weighed against the risk of a conservative approach. Indications for intervention
• 'Expanding' haematoma associated with the AVM
• Risk of haemorrhage, especially - younger patients with many years 'at risk'
• Progressive neurological deficit.
Operative removal may not benefit epilepsy control. Methods of treatment
Operation: Excision - complete excision of the AVM (confirmed by per- or postoperative angiography) is the most effective method of treatment. Image guided surgery (see page 372) may aid localisation of small AVMs or cavernous malformations. Some deeply situated lesions in the basal ganglia or brain stem are inoperable in view of the risk of neurological deficit.
Stereotactic radiotherapy: Standard radiotherapy is of no value in the treatment of AVMs, but focused beams either from multiple cobalt sources or from a linear accelerator, can obliterate up to 80% of lesions under 3 cms in diameter within two years of treatment. Results are far less encouraging for larger lesions, although a combination of embolisation and stereotactic radiotherapy may provide an alternative treatment method for large inoperable AVMs in the future. Although avoiding direct operative damage, stereotactic irradiation destroys tissue locally at the target site. The larger the dose, the greater the chance of AVM obliteration, but the greater the risk of neurological deficit from local tissue destruction. A further disadvantage is the possible delay of up to two years before obliteration occurs. Despite this, stereotactic irradiation may 290 prove ideal for some deeply situated lesions.
Feeding vessels from middle and anterior cerebral arteries
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