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Vascular anomalies are an important cause of primary intracerebral and subarachnoid haemorrhage. They tend to be seen in younger patients. An arteriovenous malformation is made up of a tangle of arteries and veins but without the usual intervening capillary bed which protects veins from exposure to systemic blood pressure. They can be found anywhere in the brain as well as the spinal cord and dura and surface of the brain. The main concern is that they can bleed. Until then they are usually silent though they can cause focal seizures and even TIA like episodes. Very rarely large superficial AVMs may produce an audible bruit which may be audible to patient and doctor. They come to attention when they cause an acute haemorrhagic stroke with headache and focal signs or subarachnoid haemorrhage with a thunderclap headache and neck stiffness and coma.

They can be seen pre-bleed on CT. These can be about 3-5 cm in size and can exert a mass effect. Many however are asymptomatic. Paradoxically small AVMS have a higher risk of bleeding. Imaging is useful. Non contrast CT may just show calcification or blood if there has been recent bleeding. MRI is more useful and will show up the vessels and a draining vein. Angiography is the gold standard. Imaging may be delayed until there has been some clot resolution to allow better visualisation. Angiography may allow pressures to be measured directly or indirectly by assessing the passage of contrast through the lesion. A high pressure within the nidus of the lesion is associated with and increased risk of bleeding. Management depends upon an assessment of the risk of bleeding and intervention. Superficial and small AVMS with a single feeding arterial branch draining to a cortical vein do best. Radiotherapy can be used to treat deep lesions with an intention to cause thrombosis of the lesion. Embolisation of large deep lesions may also be attempted.

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