Arteriovenous Malformations

Arteriovenous malformations are associated with headaches, seizures, and intracerebral bleeds in younger patients. Arteriovenous malformations are abnormalities of cerebral blood vessels which occur early in fetal development. These congenital anomalies cause problems because of a direct connection between the arterial system and the venous system with no interposed capillary bed to reduce systolic pressure. Thus, dilated arteries feed into the tangled mass of blood vessels of varying sizes and then spill blood under systolic pressure directly into the venous system, resulting in dilation of the weaker vessel walls of the veins. The lesion is usually supplied by one or more large arteries derived from one or both cerebral hemispheres and it drains through one or more veins.

Arteriovenous malformations may account for up to 1/7 of all intracranial aneurysms with up to 280,000 people per year affected. Other sources place the incidence at a rate of approximately 2,400 cases per year. Arteriovenous malformations rarely produce symptoms prior to the age of 10 years and most commonly become symptomatic during the second and third decades with male and female incidence approximately equal.

The signs of arteriovenous malformation (AVM) include intracranial hemorrhage, seizures, headaches, cranial bruits, and other focal neurological signs. Forty to sixty percent of AVM patients present with hemorrhage. Intracranial hemorrhage associated with AVMs most commonly occurs between 21 and 40 years of age. Patients may present with headache, nausea, vomiting, and possibly fever (all cardinal signs of subarachnoid hemorrhage) but these symptoms are much less severe than with subarachnoid hemorrhage, possibly due to the fact that the pressure associated with the AVM is lower than the pressure associated with a ruptured berry aneurysm or intracerebral hematoma. Therefore, the mortality rate (10%) associated with this condition is less than with subarachnoid hemorrhage and the danger associated with rebleeding is also much less. Patients may also present with a history of previous intracranial bleeding. One third of all operated AVMs demonstrate signs of old hemorrhage, suggesting that many of these intracranial bleeds may be clinically subtle or so mild that they often go misdiagnosed. Smaller AVMs are more likely to bleed than larger ones and bleeding into the brain is more likely to produce seizures than hemiparesis. In fact, seizures may precede the onset of symptoms commonly associated with intracranial hemorrhage by several years. In patients with diagnosed, unruptured arteriovenous malformations, over two thirds of these affected patients will bleed over a 20 year period. The risk of rupture of a known AVM seems to be unrelated to exercise. Pregnancy may produce a minor risk, with most hemorrhages occurring between the 15th and 20th week of gestation. In cases where there is a known AVM, the pregnant patient may choose to deliver via cesarean section to avoid possible complications due to prolonged valsalva maneuvers encountered during normal delivery.

Seizures are almost as frequently noted as intracerebral hemorrhage in AVM patients, especially if the lesion involves the cortical surface. The incidence rate for arteriovenous malformation induced seizures runs between 28% and 67% and seizures can occur at any age. Seizures are the most common initial symptoms of AVM between the ages of 11 and 20 years. Twenty-five percent of patients may have a seizure as the initial symptom of the AVM without experiencing a preceding hemorrhage and more than 50% of AVM patients experience at least one seizure prior to the age of 30, with recurrent seizures noted in 30% of afflicted patients. Seizures are noted more frequently when the arteriovenous malformation has a more anterior location within the brain than when it has a more occipital location. Additionally, larger AVMs are twice as likely to produce seizures as the smaller AVMs. Seizures associated with AVMs may be focal or generalized and 52% are classified as mild, 31% are moderate, and 17% are classified as severe seizures.

Headaches asssociated with arteriovenous malformations are usually of the migrainous variety and occur 5% to 50% of patients. These headaches tend to begin in the second decade and headaches may be generalized, unilateral, focal, continuous, or intermittent. Migraine-like symptoms associated with AVM headaches include the presence of a visual aura, fortifications spectra, and a well-localized, unilateral throbbing headache. However, in some cases, the migraine-like features encountered with the AVM are different from those noted in classic migraine headaches. Some AVM patients experience a persistence of the aura after the headache begins and ceases while others experience the initiation of the aura after the headache subsides. These latter features may aid in the differential diagnosis between a classic migraine and the headache associated with the arteriovenous malformation.

Cranial bruits can occur at any age and are caused by arterial feeders to the AVM that arise from dural arteries. The vascular murmur is synchronous with the pulse and may be noted in up to 25% of cases. The most common locations for aucultation of the bruits are over the eyeball and over the mastoid. Neurological deficits associated with AVMs include dementia, aphasia, cranial nerve compression, visual field deficits, and mild to severe hemiparesis.

References

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