Arteriovenous Malformations

Essentials of Diagnosis

• Sudden onset of subarachnoid or intracerebral hemorrhage

• Distinctive neurologic signs reflect the region of the brain involved

• Signs of meningeal irritation in patients presenting with subarachnoid hemorrhage

• Seizures or focal deficits may occur

General Considerations

• Result from a localized maldevelopment of part of the primitive vascular plexus

• Consist of abnormal arteriovenous communications without intervening capillaries

• Vary in size, ranging from massive lesions that are fed by multiple vessels and involve a large part of the brain to lesions so small that they are hard to identify at arteriography, surgery, or autopsy

• In approximately 10% of cases, there is an associated arterial aneurysm, while 1–2% of patients presenting with aneurysms have associated arteriovenous malformations (AVMs)

• Clinical presentation may relate

  • To hemorrhage from the malformation or an associated aneurysm

  • To cerebral ischemia due to diversion of blood by the anomalous arteriovenous shunt or due to venous stagnation

• Regional maldevelopment of the brain, compression or distortion of adjacent cerebral tissue by enlarged anomalous vessels, and progressive gliosis due to mechanical and ischemic factors may also be contributory

Demographics

• Up to 70% of AVMs bleed, most commonly before the age of 40

• Approximately 10% of cases are associated with arterial aneurysms, while 1–2% of patients with aneurysms have AVMs

Symptoms and Signs

• Initial symptoms consist of

  • Hemorrhage in 30–60% of cases

    • Commonly intracerebral as well as into the subarachnoid space

    • Fatal in about 10% of cases

  • Recurrent seizures in 20–40%: more likely with frontal or parietal AVMs

  • Headaches in 5–25%

    • Especially likely when the external carotid arteries are involved in the malformation

    • Sometimes simulate migraine but more commonly are nonspecific in character, with nothing about them to suggest an underlying structural lesion

  • Miscellaneous complaints (including focal deficits) in 10–15%

• Brainstem and cerebellar AVMs may cause obstructive hydrocephalus

• Abnormal mental status and signs of meningeal irritation in patients with subarachnoid hemorrhage

• Additional findings may help localize the lesion and sometimes indicate that intracranial pressure is increased

• Cranial bruit

  • Always suggests the possibility of a cerebral AVM

  • May also be found with aneurysms, meningiomas, acquired arteriovenous fistulas, and arteriovenous malformations involving the scalp, calvarium, or orbit

  • Best heard over the ipsilateral eye or mastoid region

  • May be some help in lateralization but no help in localization

  • Absence of a bruit does not exclude the possibility of AVM

Differential Diagnosis

• Aneurysmal hemorrhage

• Intracerebral hemorrhage from other causes

• Space-occupying lesion, eg, brain tumor

Imaging Studies

• CT scanning

  • Indicates whether subarachnoid or intracerebral bleeding has recently occurred

  • Helps localize source of bleeding

  • May reveal the AVM

• Arteriography

  • If the source of hemorrhage is not evident on the CT scan, arteriography is necessary to exclude aneurysm or AVM. MR angiography is not always sensitive enough for this purpose

  • Even if the findings on CT scan suggest AVM, bilateral arteriography of the internal and external carotid and vertebral arteries is required to establish the nature of the lesion

  • AVMs typically appear as a tangled vascular mass with distended tortuous afferent and efferent vessels, a rapid circulation time, and arteriovenous shunting

• MRI typically reveals the lesion but does not define its blood supply

Diagnostic Procedures

• Electroencephalography

  • Indicated in patients with seizures

  • May show consistently focal or lateralized abnormalities resulting from the underlying cerebral AVM

Medications

• In patients presenting solely with seizures, anticonvulsant drug (Table 24–2) treatment is usually sufficient, and surgery is unnecessary

Surgery

• Surgical treatment is justified to prevent further hemorrhage when AVMs have bled, provided that the lesion is accessible and the patient has a reasonable life expectancy

• Surgical treatment is appropriate

  • If intracranial pressure is increased

  • To prevent further progression of a focal neurologic deficit

• Definitive operative treatment consists of excision of the AVM if it is surgically accessible

Therapeutic Procedures

• Embolization

  • Performed when AVMs are inoperable

  • Although risk of hemorrhage is not reduced, neurologic deficits may be stabilized or even reversed by this procedure

  • More commonly performed as an adjunct to surgery or radiosurgery

  • Also done to treat intranidal aneurysms

• Stereotactic radiosurgery is also useful in the management of inoperable cerebral AVMs

Follow-Up

• Serial MRIs help monitor malformations that are not treated surgically

Complications

• Communicating or obstructive hydrocephalus may occur and lead to symptoms

Prognosis

• Depends on site of malformation and whether it has bled

• Malformations that have bled once are more likely to bleed again, at an approximate rate of 4.5% annually

• A higher risk of bleeding is also observed if there is an associated aneurysm, deep venous drainage, or deep brain location; size of the malformation and patient sex are not associated with risk of hemorrhage

When to Refer

• All patients

When to Admit

• All patients with a subarachnoid or cerebral hemorrhage

• All patients for detailed imaging

• All patients undergoing surgical or endovascular treatment